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6/01 cJCIRCfDateDue.p65-p.15

STRUCTURE/PROPERTY RELATIONSHIPS OF POLYMERS
CONTAINING HYBRID NANO-FILLER---
POLYHEDRAL OLIGOMERIC SILSESQUIOXANES (POSS)
By

Haiping Geng

A DISSERTATION
Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of
DOCTOR OF PHILOSOPHY

Department of Chemical Engineering & Materials Science

2002

Reg
pol}

Del}

rinto]

ABSTRACT
STRUCTURE/PROPERTY RELATIONSHIPS OF POLYMERS
CONTAINING HYBRID NANO-FILLER ---
POLYHEDRAL OLIGOMERIC SILSESQUIOXANES (POSS)
By
Haiping Gen g

Polyhedral Oligomeric Silsesquioxane (POSS) is a three-dimensional
structurally well-defined cage-like molecule represented by formula (RSiOl_5)n
(n = 6, 8, 10 or higher, R is an organic group). POSS macromers have an
inorganic silica-like core, which is surrounded by organic groups, and the
physical size of the POSS cage is about 1.5 nm. Because of their hybrid nature
and nanometer-scale feature, as shown in this study, POSS macromers were
dispersed in a molecular level into polymeric systems by blending, in effect
achieved POSS/Polymer nanO—blends. The POSS macromers used in this work
were cubic-caged POSS macromers bearing different organic corner groups.
polystyrene (PS) and polydimethyl siloxane (PDMS) were used as model
polymers.

The investigations involved in this work include two parts. In the first
part, the microstructures and thermal properties of the POSS macromers were
investigated by using X-ray diffractometer, Differential Scanning Calorimetry
(DSC), and Thermogravimetric Analysis (TGA). In the second part, the
morphologies of POSS/Polymer blends were examined using Transmission

Electronic Microscopy (TEM), and X-ray diffractometer. Their thermal and

rheological properties were studied with DSC, TGA, and Rheometer.

Th
Cage BID
macrome'
macrome
POSS Ir.
undergoc

Th
that dep
structure
morpholt
homogen

Tl
under e1:
result 0:
9015mm

tum sho

(D

lrelatt

“rider 1;“

The results of this work showed that different corner groups on the POSS
cage affected the morphological structures and properties of the POSS
macromers. The higher the degree of the symmetry and regularity of the POSS
macromers and the smaller the size of the corner groups, the more ordered the
POSS macromers. The POSS macromers with functionalities, which may
undergo chemical cross-linking reactions, possessed high thermal stabilities.

The morphology studies of POSS/PS and POSS/PDMS blends showed
that depending on the attached organic groups on the POSS cages, the
structures Of the polymer matrix and the composition Of the blends, the
morphologies Of the POSS/polymer blends ranged from complete separation to
homogeneous dispersion in the nanoscopic scale.

The rheological investigations of the POSS/PDMS blends revealed that
under elevated temperatures, gelation occurred in the POSS/PDMS blends as a
result of intermolecular association between POSS nanO-fillers and PDMS
polymer chains. The formation of gel exhibited a solid-like behavior, which in
turn showed a significantly improved creep resistance. Since the formation of
gel relates with only physical interaction, the POSS/PDMS gel can be destroyed

under large stain/stress and re-formed under elevated temperatures.

WHC

DEDICATION

To

MY FAMILY AND MY FRIENDS

WHO LOVED ME AND SUPPORTED ME DURING THE PAST YEARS!

iv

COLTS”

Greg

who

Who

FIG

dis'

ACKNOWLEDGEMENTS

I would like to thank my advisor, Dr. Andre Y. Lee, for his
guidance, support and encouragement throughout this entire research. I
also would like to express my gratefulness to the members of my
committee, Dr. Dahsin Liu, Dr. Krishnamurthy Jayaraman, and Dr.
Gregory L. Baker for their input and guidance.

In addition, great appreciation must be given to Mr. Ben Simkin,
who assisted me in TEM and X-ray operation, and Mr. Robert Pcionek,
who helped me in my dissertation writing.

Special thanks go to the Air Force Research and Laboratory, state
Of Michigan-Research Excellent Funds for the financial support. I also
like to thank General Electric Silicone and Hybrid Plastics, Inc. who
supplied some materials used in this work.

Last, I’d like to express my thankfulness to Graduate School for
providing me the Graduate Office Fellowship, so I could complete my

dissertation in the spring of 2002.

Lhtoi'

thoi

Cbaph

Cba

TABLE OF CONTENTS

List of Tables ------------------------------------------------------------------------- xi
List of Figures ----------------------------------------------------------------------- xii
Chapter 1: Introduction ------------------------------------------------------------- 1
1.1 Statement Of Problems --------------------------------------------------- l

1.2 Introduction Of this Research Work ------------------------------------ 4

1.2.1 Objective ---------------------------------------------------------- 4

1.2.2 Research Approach ---------------------------------------------- 4

1.2.3 Contributions to the POSS Nano-Technology ---------------- 7

Chapter 2: Literature Review ----------------------------------------------------- 9
2.1 Chemistry of Silsesquioxanes -------------------------------------------- 9

2.1.1 Abbreviations for Silsesquioxanes ------------------------- -10

2.1.2 Brief History of Silsesquioxanes ---------------------------- 10

2.1.3 Structure and Classification of Silsesquioxanes ------------ 11

2.1.4 Synthesis of Silsesquioxanes ---------------------------------- 12

2.2 Polymeric Materials Containing POSS ------------------------------- -21

2.2.1 Organic—Inorganic Hybrid Polymers Containing POSS ----- 21

2.2.2 POSS/Polymer Nanoscopic Materials ------------------------ 27

PART I: Investigations of POSS Macromers ---------------------------------- 29

vi

Chapter 3

31

33

 

14

PARIll

Preface .

Chapier

BleDds..

4i

Chapter 3: Structure-Property Studies of POSS Macromers --------------- 30

3.1 Introduction -------------------------------------------------------------- 30

3.2 Experimental ------------------------------------------------------------- 31
3.2.1 Materials -------------------------------------------------------- 31

3.2.2 Sample Preparations ------------------------------------------- 31

3.2.3 Characterization Techniques -------------------------------- 35

3.3 X-Ray Crystallographic Analysis Of POSS Macromers -------------- 36

4.3.1 Effects of POSS Corner Groups ------------------------------ 36

4.3.2 Summary -------------------------------------------------------- 45
3.4 Thermal Stability Study of POSS Macromers -------------------------- 47

3.4.1 Effects of POSS Corner Groups ------------------------------ 51

3.4.2 Summary ----- . -------------------------------------------------- 63

3.5 Transition Temperatures Of POSS Macromers ----------------------- 64

3.5.1 Effects of POSS Corner Groups ------------------------------ 64

3.5.1 Summary -------------------------------------------------------- 73

PART II: Investigations on POSS/Polymer Blends --------------------------- 74
Preface -------------------------------------------------------------------------------- 75

Chapter 4: Morphology and Interaction Studies of POSS/Polystyrene (PS)

Blends ---------------------------------------------------------------------------------- 78
4.1 Introduction --------------------------------------------------------------- 78
4.2 Experimental -------------------------------------------------------------- 79

vii

4.2.1 Materials -------------------------------------------------------- 79
4.2.2 Sample Preparations ------------------------------------------- 80
4.2.3 Characterization Techniques --------------------------------- 80

4.3 Morphological Studies of POSS/PS Blends by Transmission
Electronic Microscope (TEM) ----------------------------------------------- 82

4.3.1. Effects of POSS Macromers with Different Corner Groups
on the Morphologies of POSS/PSZM Blends (50wt% POSS

Loading) --------------------------------------------------------------- 82
4.3.2. Effects of POSS Loading on the Morphologies of
POSS/PSZM Blends -------------------------------------------------- 89
4.3.3 Effects of PS Molecular Weight on the Morphologies Of
POSS/PS Blends ------------------------------------------------------ 93
4.3.4 Discussion ------------------------------------------------------- 94
4.3.5 Summary -------------------------------------------------------- 96
4.4 X-Ray Crystallographic Analysis of POSS/PS Blends -------------- 96
4.4.1 Effects of POSS Chemistry and POSS Loading ... --------- 97
4.4.2 Effects of PS Molecular Weight ----------------------------- 108
4.4.3 Summary ------------------------------------------------------- 109
4.5 Glass Transitions Of POSS/PS Blends -------------------------------- 110
4.5.1 Effects of POSS Chemistry and POSS Loading ----------- 110
4.5.2 Discussion ----------------------------------------------------- 121
4.5.3 Summary ------------------------------------------------------- 122
4.6 Thermal Stability Studies of POSS/PS Blends ---------------------- 123
4.6.1 Effects of POSS Chemistry and POSS Loading ----------- 123
4.6.2 Summary ----------------------------------------------------- 129

viii

Chapter 5
(PDMS) 1%

5.l

‘

5.-

5.4
it».

 

Chapter 5: Morphology and Properties of POSS/ Polydimethyl Siloxane

(PDMS) Blends --------------------------------------------------------------------- 130
5.1 Introduction ------------------------------------------------------------- 130
5.2 Experimental ------------------------------------------------------------ 132

5.2.1 Materials ------------------------------------------------------- 132

5.2.2 Sample Preparations ------------------------------------------ 132

5.2.3 Characterization Techniques --------------------------------- 133

5.3 Morphological Structures of POSS/PDMS Blends ------------------ 135
5.4 Thermal Stability Studies of POSS/PDMS Blends By
Thermogravimetric Analysis (TGA) -------------------------------------- 141
5.5 Rheological Properties of POSS/PDMS Blends --------------------- 148
5.5.1 Effects of POSS Macromers on the Rheologlcal Behaviors of
PDMS ----------------------------------------------------------------- 148

5.5.2 Gelation Process of POSS/PDMS Blends ------------------ 150
5.5.2.1 Background Of Gelation ---------------------------- 150

5.5.2.2 Gelation Process of POSS/PDMS Blends -------- 154

5.5.3 Rhological Properties of Gelled POSS/PDMS Blends ----159

5.5.4 Physical Nature of POSS/PDMS Gelation ----------------- 164
5.5.4.1 DSC Result of POSS/PDMS Blend --------------- 164
5.5.4.2 Destruction of Gelled POSS/PDMS Blends and Re-
Gelation - ----------------------------------------------------- 165
5.5.4.3 Physical Nature of POSS/PDMS Gelation ------- 173

5.5.5 Effects of Compositions and Experimental Conditions on the
Gelation Processes of POSS/PDMS Blends ----------------------- 174

5.5.5.1 Rate of Storage Modulus Change (R0)—

Characterization of the Gelation Rates Of the POSS/PDMS
Blends --------------------------------------------------------- 174

ix

Chapter

Referenc

 

5.5.5.2 Effects of the POSS Chemistry on the Gelation

Processes of the POSS /PDMS Blends -------------------- 175
5.5.5.3 Gelation Behaviors of POSS/PDMS Blends with
Different POSS Concentrations --------------------------- 179
5.5.5.4 Influence of PDMS Molecular Weight on the
Gelation Rates of the POSS/PDMS Blends -------------- 180
5.5.5.5 Effects of the Annealing Temperatures on the
Gelation Rate of the POSS/PDMS Blends ---------------- 182
5.5.6 Discussion ----------------------------------------------------- 183
5.5.6.1 Gelation Mechanism of the POSS/PDMS Blends -----
------------------------------------------------------------------ 183

5.5.6.2 Gelation Process of the POSS/PDMS Blends ----187

5.5.7 Summaries ----------------------------------------------------- 188

Chapter 6: Conclusions and Recommendations ------------------------------ 190
6.1 Conclusions ---------------------- ' ---------------------------------------- l 90

6.2 Recommendations ------------------------------------------------------- 196
References --------------------------------------------------------------------------- 198

Table 3-
Slacrome

Table 3..
narentnes
r

times) -

Table 3.4

lnorsarttc

Table 4.1:

Table 4.2:
X-ray tht

Table «1.3:
X-Ifl} Dtt‘f

Table 4.4:
Blentii (in

Table 4.5:
X'fii} D11“
Table 46
hi) of:
Table 4}
Blends lffr

Table 4.5
lfrOm X-T.

Table 49

 

Table 4.1

Table 5']

 

LIST OF TABLES

Table 3.1: Abbreviations, Chemical formulae, and Molecular Weight Of POSS
Macromers 32

 

Table 3.2: Peak Positions (unit: °2 0) and their corresponding d-spacing (as shown in
parentheses, unit A) of POSS Macromers (Summarized from their X-ray diffraction

 

 

 

 

 

 

 

 

 

 

 

 

curves) 43
Table 3.3: Thermal Stabilities of POSS Macromers with different Comer Groups ------ 58
Table 3.4: Molecular Weight of POSS Macromers, and the Weight Percentage of their
Inorganic Si-O Portion and Organic C-H Portion 59

Table 3.5: Transition Temperatures of POSS Macromers (DSC Results) 72
Table 4.1: Phase Characteristics of POSS/PSZM Blends (50 wt% POSS) 83
Table 4.2: Comparison of Peak Positions of CngOSS and CngOSS/PSZM Blends (from
X-ray Diffraction Curves in Figure 4.16) 98
Table 4.3: Comparison of Peak Positions of CngOSS and CngOSS/PS2M Blends (from
X-ray Diffraction Curves in Figure 4.17) 99
Table 4.4: Comparison of Peak Positions of StyrenylgPOSS and StyrenylgPOSS/PSZM
Blends (from X-ray Diffraction Curves in Figure 4.18) 101

Table 4.5: Comparison of Peak Positions of PthOSS and PthOSS/PS2M Blends (from
X-ray Diffraction Curves in Figure 4.19) 102
Table 4.6: Comparison of Peak Positions of V3POSS and VgPOSS/PSZM Blends (from
X-ray Diffraction Curves in Figure 4.20) 103
Table 4.7: Comparison of Peak Positions of STIprPOSS and STICp7POSS IPSZM
Blends (from X-ray Diffraction Curves in Figure 4.21) 105
Table 4.8: Comparison of Peak Positions of V1Cp7POSS and VleyPOSS IPSZM Blends

(from X-ray Diffraction Curves in Figure 4.22) 106

Table 4.9: Comparison of Peak Positions of CyHeIprPOSS and CyHeleyPOSS IPSZM
Blends (from X-ray Diffraction Curves in Figure 4.23) 107

Table 4.10 Glass Transition Behaviors of POSS/PSlM Blends lll

 

 

Table 5.1: Characteristics of Polydimethyl Siloxane (PDMS) 132

xi

figutt 1.1
Cubic Slut}

Enmll
with a Per.

Eymll

Figure 2.2

.. 5 "
lrlgat'? .3

Figure I l
Condensa

Hgnl?

Figure 2.15

 

LIST OF FIGURES

Figure 1.1: Schematic Diagram of Polyhedral Oligomeric Silsesquioxane (POSS) with a

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Cubic Shape (R7YISi3012) 3
Figure 1.2: POSS Macromer with Monofunctional Group Converted to Hybrid Polymer
with a Pendent Architecture 3
Figure 2.1 Schematic Diagram of Silsesquioxanes with a Cubic Shape (ngigolz) ----- 12
Figure 2.2: Complex Products of RSiCl3 Hydrolytic Polycondensation Reaction ------- 16
Figure 2.3: Examples of Fully Condensed POSS Systems 17
Figure 2.4: Examples of Incompletely Condensed POSS Systems 18
Figure 2.5: Comer Capping of R7T4D3(OH)3 19
Figure 2.6: Incompletely Condensed Silsesquioxane Prepared by the Hydrolytic
Condensation of (c-C6H. .)SiCl3 20
Figure 2.7: Base-mediated Cleavage of Fully Condensed [C6H11)3813012] 20
Figure 2.8: Architecture Of Linear POSS-based Polymers 23
Figure 2.9: Polymerization of Methacrylates-POSS Homopolymer and Copolymer ------ 24
Figure 2.10: Free Radical Polymerization of Styryl-POSS based Copolymer ------------- 25
Figure 2.11: POSS-Siloxane Copolymer 25
Figure 2.12: Schematic of the Curing Cycle of the POSS-Epoxy System 26
Figure 3.1: POSS Macromers With Different Comer Groups 33
Figure 3.2: X-ray Diffraction Profile of CngOSS Macromer 37
Figure 3.3: X-ray Diffraction Profile of CngOSS Macromer 37
Figure 3.4: X-ray Diffraction Profile of StyrenylgPOSS Macromer 38
Figure 3.5: X-ray Diffraction Profile of PthOSS Macromer 38
Figure 3.6: X-ray Diffraction Profile of VgPOSS Macromer 39

Figure 3.7: X-ray Diffraction Profile of IsobugPOSS Macromer 39

 

xii

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heue3.

Ewell

Egm3$

Eye}
tam}

Emmi
h

L

 

 

Figure 3.8: X-ray Diffraction Profile of STIprPOSS Macromer
Figure 3.9: X-ray Diffraction Profile of Styrenylle7POSS Macromer
Figure 3.10: X-ray Diffraction Profile of CyHele7POSS Macromer
Figure 3.11: X-ray Diffraction Profile of Vle7POSS Macromer
Figure 3.12: X—ray Diffraction Profile of STIIsobu7POSS Macromer
Figure 3.13: X—ray Diffraction Profile of Styrenylllsobu7POSS Macromer --------------
Figure 3.14: TGA curve of CngOSS Macromer
Figure3.15: TGA curve Of CngOSS Macromer
Figure 3.16: TGA Curve Of StyrenylgPOSS Macromer
. Figure 3.
Figure 3.
Figure 3.
Figure 3.
Figure 3.
Figure 3.
Figure 3.
Figure 3.

Figure 3.

17:

18:

19:

20:

21:

22:

23:

24:

25:

 

 

 

40

4O

41

41

 

 

42

42

 

 

 

 

TGA Curve Of PthOSS Macromer

TGA Curve of Isobu3POSS Macromer

 

 

TGA Curve of V3POSS Macromer

 

TGA Curve of STlCmOSS Macromer

TGA Curve of StyrenleCp7POSS Macromer

49

50

50

51

51

52

52

 

 

TGA Curve of CyHele-IPOSS Macromer

TGA Curve of V1Cp7POSS Macromer

 

 

TGA Curve of STllsobu7POSS Macromer

TGA Curve Of Styrenylllsobu7POSS Macromer

 

53

53

54

54

Figure 3.26: TGA Curves of the R3POSS Macromers: CngOSS, CngOSS,

StyrenylgPOSS, PthOSS, IsobugPOSS, and V3POSS

 

55

Figure 3.27: TGA Comparisons of STle7POSS, Styrenylth7POSS, CyHele7POSS,

and V1Cp7POSS with CngOSS

 

56

Figure 3.28: TGA Comparisons of Styrenylllsobu7POSS, and ST1Isobu7POSS with

ISODUgPOSS

 

xiii

57

 

Figure 3.29: DSC Curve Of CngOSS Macromer

Figure 3.30: DSC Curve of CngOSS Macromer

 

 

Figure 3.31: DSC Curve Of StyrenylgPOSS Macromer

Figure 3.32: DSC Curve Of PthOSS Macromer

 

 

Figure 3.33: DSC Curve of V3POSS Macromer

 

Figure 3.34: DSC Curve of ISObUgPOSS Macromer

Figure 3.35: DSC Curve of STleyPOSS Macromer

 

 

Figure 3.36: DSC Curve of Styreny11Cp7POSS Macromer

Figure 3.37: DSC Curve Of CyHele7POSS Macromer

 

 

Figure 3.38: DSC Curve of V1Cp7POSS Macromer

Figure 3.39: DSC Curve Of STIIsobu7POSS Macromer -

 

 

Figure 3.40: DSC Curve of Styrenylllsobu7POSS Macromer

Figure 4. 1: TEM Image of CngOSS/PSZM Blend (50 wt% POSS)

66

66

67

67

68

68

69

69

7O

70

71

71

84

 

 

Figure 4. 2: TEM Image of STIprPOSS/PSZM Blend (50 wt% POSS)

84

85

 

Figure 4. 3: TEM Image of StyrenylgPOSS/PS2M Blend (50 wt% POSS)

Figure 4. 4: TEM Image of PthOSS/PSZM Blend (50 wt% POSS)

86

 

87

 

Figure 4. 5: TEM Image of CngOSS/PSZM Blend (50 wt% POSS)

Figure 4. 6: TEM Image of VgPOSS/PSZM Blend (50 wt% POSS)

87

 

Figure 4. 7: TEM Image of CyHe1Cp7POSS/PS2M Blend (50 wt% POSS) ..............

Figure 4. 8: TEM Image Of V1Cp7POSS/PS2M Blend (50 wt% POSS)

88

88

 

 

Figure 4. 9: TEM Image of CngOSS/PS2M Blend (20 wt%)

 

Figure 4. 10: TEM Image of CngOSS/PSZM Blend (20 wt%)

Figure 4. 11: TEM Image or StyrenylgPOSS/PSZM (20 wt%)

91

 

xiv

Figure 4. 12:TEM Image Of PthOSS/PSZM Blend (20 wt%) 91

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4. 13: TEM Image of VgPOSS/PSZM Blend (20 wt%) 92
Figure 4. 14: TEM Image of STICp7POSSlPS2M Blend (20 wt%) 92
Figure 4. 15: TEM Image of PthOSS/P8216K Blend (20 wt%) 93
Figure 4. 16: X-Ray Diffraction Profile Of CngOSS/PSZM Blends 97
Figure 4.17: X-Ray Diffraction Profile of CngOSS/PSZM Blends 99
Figure 4.18: X-Ray Diffraction Profile of StyrenylgPOSS/PSZM Blends 100
Figure 4. 19: X-Ray Diffraction Profile of PthOSS/PS2M Blends 101

Figure 4. 20: X-Ray Diffraction Profile Of VgPOSS/PSZM Blends 103
Figure 4.21: X-Ray Diffraction Profile of STIprPOSS/PSZM Blends 104
Figure 4.22: X-Ray Diffraction Profile of Vle-IPOSS/PSZM Blends 105

Figure 4.23: X-Ray Diffraction Profile of CyHele7POSS/PS2M Blends 106
Figure 4.24: X-ray Diffraction Profiles of CngOSS/PS (20wt%) Blends with Different
M.W. PS 108
Figure 4.25: X-ray Diffraction Profiles of STleyPOSS/PS (20wt%) Blends with
Different M.W. PS 109

Figure 4.26: DSC Curve of PSlM 112

Figure 4.27: DSC Curve of PSIM/CngOSS (20wt% POSS Loading) 112
Figure 4.28: DSC Curve of PSlM/CngOSS (50wt% POSS Loading) 113
Figure 4.29: DSC Curve Of PSIM/CngOSS (80wt% POSS Loading) 113
Figure 4.30: DSC Curve of PSIM/StyrenylgPOSS (20wt% POSS Loading) ------------ 114
Figure 4.31: DSC Curve of PSIM/StyrenylgPOSS (50wt% POSS Loading) ------------- 114
Figure 4.32: DSC Curve of PSlM/StyrenylgPOSS (80wt% POSS Loading) ------------- 115

Figure 4.33: DSC Curve Of PSlM/PthOSS (20wt% POSS Loading) 115

 

XV

thurt 4-

Egmié

Egm4é

Enr4.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.34: DSC Curve of PSlM/PthOSS (50wt% POSS Loading) 116
Figure 4.35: DSC Curve of PSlM/PthOSS (80wt% POSS Loading) 116
Figure 4.36: DSC Curve of PSlM/IsobugPOSS (20wt% POSS Loading) 117
Figure 4.37: DSC Curve of PSlM/IsobugPOSS (50wt% POSS Loading) 117
Figure 4.38: DSC Curve of PSlM/IsobUgPOSS (80wt% POSS Loading) 118
Figure 4.39: DSC Curve of PSIM/STIprPOSS (20wt% POSS Loading) 118

Figure 4.40: DSC Curve of PSlM/ ST1Cp7POSS (50wt% POSS Loading) 119
Figure 4.41: DSC Curve of PSlM/STIprPOSS (80wt% POSS Loading) 119
Figure 4. 42: TGA Curves of PS2M/Cp3POSS Blends 124
Figure 4.43: TGA Curves of PS2M/CngOSS Blends 124
Figure 4.44: TGA Curves Of PS2M/V3POSS Blends 125
Figure 4. 45: TGA Curves of PS2M/ST1Cp7POSS Blends 125
Figure 4.46: TGA Curves Of PS2M/V1Cp7POSS Blends 126
Figure 4. 47: TGA Curves Of PSZM/CyHele7POSS Blends 126
Figure 4.48: TGA Curves of PS2M/StyrenylgPOSS Blends 127
Figure 4.49: TGA Curves of PSZM/PthOSS Blends 127
Figure 5.1: Chemical Structure of Polydimethyl Siloxane (PDMS) 130
Figure 5.2: X-ray Profile of SE72/CngOSS Blend (20 wt% POSS loading) ----------- 136

Figure 5.3: X-ray Profile of SE72/V3POSS Blend (20 wt% POSS loading) ------------ 136

Figure 5.4 X-ray Profile of SE72/Isobu3POSS Blend (20 wt% POSS loading) --------- 137
Figure 5.5: X-ray Profile of SE72/ST1Cp7POSS Blend (20 wt% POSS loading) ------- 137

Figure 5.6: X-ray Profile Of SE72/Styrenylle7POSS Blend (20 wt% POSS loading)-l38

Figure 5.7: X-ray Profile of SE72/CyHe1Cp7POSS Blend (20 wt% POSS loading) ----138

xvi

BflmS-
oi freque

Hams.
tam t

Figure 5.

“9&5

gelled it?

Figure 5
1305mm
3130f c

 

Figure 5.8: X-ray Profile of SE72/V1Cp7POSS Blend (20 wt% POSS loading) --------- 139
Figure 5.9: X-ray Profile of SE72/STllsobu7POSS Blend (20 wt% POSS loading) ----139

Figure 5.10: X-ray Profile Of SE72/Styrenylllsobu7POSS Blend (20 wt% POSS loading) -

 

139
Figure 5.11: TGA Curve of SE72/Cp3POSS Blend (20wt% POSS loading) ------------ 142
Figure 5.12: TGA Curve of SE72/V3POSS Blend (20wt% POSS loading) ------------- 143
Figure 5.13: TGA Curve of SE72/Isobu3POSS Blend (20wt% POSS loading) --------- 143
Figure 5.14: TGA Curve Of SE72/ST1Cp7POSS Blend (20wt% POSS loading) -------- 145

Figure 5.15: TGA Curve Of SE72/Styrenylle7POSS Blend (20wt% POSS loading) «145
Figure 5.16: TGA Curve Of SE72/CyHe1Cp7POSS Blend (20wt% POSS loading) ---- 146
Figure 5.17: TGA Curve of SE72/V1Cp7POSS Blend (20wt% POSS loading) --------- 146
Figure 5.18: TGA Curve of SE72/STIIsobU7POSS Blend (20wt% POSS loading) -----l47

Figure 5.19: TGA Curve of SE72/StyrenylllsobU7POSS Blend (20wt% POSS loading) -'--
147

 

Figure 5.20: Storage Modulus, as a function of frequency, of POSS/SE72 Blends at 30°C-
- 149

 

Figure 5.21: Comparison of Modulus (G’ and G”), and Loss Tangent (tanO), as a function
of frequency, of IsobugPOSS/SE72 Blend (10wt% POSS Loading) before annealing
(open symbols) and after annealed for 60 hours at 200°C (filled symbols) 155

 

Figure 5.22: Rheological Properties Changes of the 10 weight % Loading Isobu3POSS
/SE72 Blend with Annealing Time at 200°C 156

 

Figure 5.23: Comparison of the Storage Modulus (G’) and Loss Modulus (G”), as a
function of frequency, Of PDMS (SE72) at different annealing time at 200°C ----------- 158

Figure 5.24: Comparison of Rheological Properties, as a function of frequency, of un-
gelled and gelled IsobusPOSS/VisCIOOM (10wt%) Blend at 30°C 160

 

Figure 5.25: Storage Modulus, as a function of strain, for un-gelled and gelled
ISObllgPOSS/VISCIOOM Blends of 10wt% POSS loading. The experiment was performed
at 30°C and with angular frequency of 62.9 US 162

 

xvii

Figure

Hgmi

fing.
different I

Hflmi-
than»)

   

Figure 5.
PDMS Bl

BNmSJ
PDMS (V

Figure 5

(ENG?

 

ERmS,

EDWS;

 

Figure 5.26: Creep Behavior of the un-gelled and gelled Isobu3POSS/Visc30M (20wt%
POSS) Blends. The experiment was conducted at 30°C, and shear stress of 500Pa ---- 163

Figure 5.27: DSC Result Of IsobusPOSS/SE72 (20wt% POSS Loading) Blend under
200°C Isothermal Condition for 6hr 165

 

Figure 5.28: Creep Compliances of gelled IsobugPOSS/Visc30M (10 wt% POSS loading)
Blends under shear stresses of 5 and 10 KPa at 30°C 166

 

Figure 5.29: Shear Rate of Gelled IsobugPOSS/Visc30M Blends (10wt% POSS loading)
during creep test (under shear stresses of 5 and 10 KPa at 30°C) 167

 

Figure 5.30: Viscosity, versus time, of Gelled IsobugPOSSNisc30M Blends (10wt%
POSS loading) during creep test (under shear stresses of 5 and 10 KPa at 30°C) -------- 167

Figure 5.31: Modulus Comparison of the Gelled IsobugPOSSNisc30M Blend (10 wt%
POSS loading) before and after the 5 KPa creep test 168

 

Figure 5.32: Comparison of Modulus, as a function of frequency, of Gelled
ISObUgPOSSNiSC3OM Blends (10wt% POSS) before and after the 10 KPa creep test--l69

Figure 5.33: Re-Gelation of IsobugPOSS/Visc30M Blend (10wt%POSS) at 200°C ----170

Figure 5.34: Modulus. as a function Of frequency, Of Re-gelled IsobugPOSS/Visc30M
Blend (10wt% POSS) 30°C ‘ 171

 

Figure 5.35: Gelation Rates of Blends of PDMS (SE72) with POSS Macromers bearing
different Comer Groups (20wt% POSS Loading) at 200°C 176

 

Figure 5.36: Effects of POSS Loading on the Gelation Rates of IsobugPOSS/ PDMS
(VisclOOM) Blends 179

 

Figure 5.37: Effects of PDMS Molecular Weights on the Gelation Rates of IsobugPOSS/
PDMS Blends (20wt% Loading) 181

 

Figure 5.38: Effects of Annealing Temperatures on the Gelation Rates of IsobugPOSS/
PDMS (Visc30M) Blends (10wt% POSS Loading) 182

 

Figure 5.39: X-ray Diffraction Profiles of Styrylllsobu7POSS/PDMS (SE72) Blends
(20wt% POSS Loading) Before and After Gelation 184

 

Figure 5.40: X-ray Diffraction Profiles of StyrenylllsobuyPOSS/ PDMS (SE72) Blends
(20wt% POSS Loading) Before and After Gelation 184

 

Figure 5.41: Schematic Diagram of the Formation of the POSS-PDMS Network ------ 186

xviii

Mixture”

 

Figure 5.42: Schematic Illustration of the Gelation Process in the POSS/Polymer
Mixture 187

 

xix

11 Stat

51
flayed a
thistner
usage te

In
fdlers n
has exh
two Ch
lprocess
lillérma
nanome
“llh siz
Smentis
lthieh d

C

Ihelm;

 

Iradlll(

SITUCIL“

1
(R810

 

 

CHAPTER 1

INTRODUCTION

 

 

1.1 Statement of the Problems

Since their discovery almost 150 years ago, synthetic polymers have
played an increasingly important role in daily life. However, along with
this increased use have come more demanding requirements such as higher
usage temperature and greater resistance to oxidation, etc.

In recent years, the use of small amounts of nanoscopic inorganic
fillers in commodity polymers such as nylon, polypropylene, epoxy, etc.
has exhibited significant performance enhancement. This approach has
two characteristics. First, it combines the properties of polymers
(processability and toughness) with the properties of inorganic compounds
(thermal and oxidative stability). Second, it has an inorganic phase with a
nanometer size. NanO-phase materials belong to a new family Of materials
with size intermediate to those usually studied by chemists and material
scientists. They often exhibit enhanced physical and chemical properties,
which are sometimes dramatically different from their neat counterparts.

Our approach to organic-inorganic.nanoscopic materials involves
the incorporation of Polyhedral Oligomeric Silsesquioxanes (POSS) into
traditional polymeric systems. POSS macromer is a three-dimensional
structurally well-defined cage-like molecule represented by formula

(RSiOLs)u (n: 6, 8, 10..., R is organic corner groups). POSS technology

MSIWO
POSS ma
b} organ
otPOSS
mguuc.
POSS m
compaur

mac or

nearl) et

B:
macrom;
mmenal
Whine:-

Teacttte

 

Variety
mOHOfUr
[0 mode

 

has two unique features. First, the chemical composition is a hybrid:
POSS macromers have an inorganic silica-like core, which is surrounded
by organic groups. One example, as shown in Figure 1.1, is the structure
Of POSS macromer with a cubic shape (R7Y1Si3012). The nature of the
organic corner groups on the POSS cages determines the properties of the
POSS macromers, such as: crystallinity, solubility, reactivity and their
compatibility with polymers. Furthermore, it is also possible to modify
these organic corner groups to produce the desired functionalities.
Second, the physical size of POSS macromers is about 1.5 nm [1], which is
nearly equivalent in size to most polymer segments and coils.

Because of its hybrid nature and nanometer scale feature, POSS
macromer is a promising material for preparing nano-reinforced polymeric
materials. There are two methods to incorporate POSS macromers into
polymeric systems. First, POSS macromers, which contain functional
reactive sites, can be incorporated with organic species to produce a
variety Of organic-inorganic hybrid polymers. An example of a
monofunctional POSS macromer co-polymerized with an organic monomer
to produce a linear hybrid polymer is shown in Figure 1.2”] Second, the
organic groups surrounding the POSS framework can be made to be
compatible with polymer matrix to form blends with nanO-filler

reinforcement. These two approaches combine the best features of

polymers with the best features Of ceramics. In comparison to

 

 

 

 

 

 

 

 

R and Y: Organic Groups

Figure 1.1: Schematic Diagram of Polyhedral Oligomeric
Silsesquioxane (POSS) with a Cubic Shape (R7Y18i3012).

 

; o / —f‘ximi Y in

0/ . .
:l

 

/ ° l<
n{ 0R7! Cb i }n +mX R/s/O/SQ: 2M»
/5' ° \ <°\//°/<.

X,Y: Polymerizable or
Grafable Functionality.

 

 

 

 

 

 

Figure 1.2: POSS Macromer with Monofunctional Group
Converted to Hybrid Polymer with a Pendent Architecture.

Cantenll
cthtbli :1
Be
develop
modified
and elas
concentr
efiort tc

address

nano.nia

L2 lntr

L2.l()

and pit
POSS/P

lead to i

1'2'2 Rt

This It;

 

Pan 1: j

 

conventional filled-polymers, these POSS-containing polymers may
exhibit a significant number of enhanced properties.

Because blending is the most effective engineering approach to
develop materials with improved properties, (for example: organic
modified clay, carbon black, and fumed silica have been used in plastics
and elastomers to form nanoscopic-materials by blending), this work is
concentrated on the blending of POSS macromers with polymers in an
effort to prepare POSS/polymer nanoscopic materials. We attempt to
address fundamental issues involving in the formation of POSS/polymer
nanO-materials ----- how POSS is “molecularly” dispersed in polymeric
matrix. and what are the structure/property relationships Of these nano-

materials.

1.2 Introduction to this Research Work
1.2.1 Objective:

The objective of this research work was to study the morphologies
and properties (such as: thermal and rheological properties) of the
POSS/Polymer blends, and to develop structure-property relationships that

lead to Optimum performance of the POSS/Polymer nanO-materials.

1.2.2 Research Approach:
This work is composed of two parts:

Part I: Investigations of POSS Macromers

Stru
Chapter 3.
the corne
properties
the POSS
unng l)ti
And}sis
exahuned
higher th:
and the s
macronie:
undergo

stabihtie

Partll: I

Structure/Property Studies of POSS macromers were reported in
Chapter 3. In particular, we were interested in understanding the impacts of
the corner groups on the morphologies (ordered or amorphous) and
properties (such as transition temperature, decomposition temperature) of
the POSS macromers. Thermal property and stability were investigated
using Differential Scanning Calorimeter (DSC), and Thermogravimetric
Analysis (TGA), while crystalline structures of POSS macromers were
examined using wide angle X-ray diffraction. The results showed that the
higher the degree of the symmetry and regularity of the POSS macromers
and the smaller the size of the corner groups, the more ordered the POSS
macromers. And the POSS macromers with functionalities, which may
undergo chemical cross-linking reactions, possessed high thermal

stabilities.

Part II: Investigations of POSS/Polymer Blends

Studies of the morphologies and properties Of the POSS/Polystyrene
(PS) and POSS/Polydimethyl Siloxane (PDMS) mixtures are described in
Chapter 4 and Chapter 5, respectively.

The morphologies of the POSS/polymer blends and the interface
between the two components are the key points in developing molecular
dispersion of POSS nanO-cluster in polymers with desired properties. The
effects of the POSS macromers with varying corner groups, polymers with

different molecular weights, and amounts of POSS macromers used on the

morphOlOS
Microscop

the intera;

 

The
depending
chemical
POSS/pol
in the nar

Th
was ex:
gelation
In order
of the .
iollowi
macron
P013me
exPeril

“‘33 pc

morphologies of the blends were examined using a Transmission Electron
Microscope (TEM), and X-ray diffractometer. DSC was used to investigate
the interactions between POSS macromers and PS.

The morphologies of the POSS/PS and POSS/PDMS showed that
depending on the attached chemical groups on the POSS cages and the
chemical features of the polymer matrix, the morphologies of the
POSS/polymer ranged from complete separation to homogeneous dispersion
in the nanoscopic scale.

The interaction between POSS with varying organic groups in PDMS
was examined using rheological techniques. We found that physical
gelation occurred in PDMS with molecularly dispersed POSS incorporation.
In order to examine the nature of the POSS/PDMS gelation, the properties
of the gelled POSS/PDMS systems were studied, and the impacts of the
following factors on the POSS/PDMS associations were investigated: POSS
macromers with different chemical structures, molecular weight of
polymer, annealing temperature, and POSS concentration. Based on the
experimental results, the gelation mechanism of the POSS/PDMS blends
was postulated.

The rheological results of the POSS/PDMS blends revealed that
under elevated temperatures, the gelation occurred in the POSS/PDMS
blends was a result of intermolecular association between POSS filler and
PDMS polymer chains. The formation of gel exhibited a solid-like

behavior. Gelled POSS/PDMS blends exhibited high modulus and

ngnifiea
nonlinea
physical
stain/stir
POSS c
revealed
macromt
macrom:
gelation
tempera
molecul

lr
STOUPS (

also int

1.2.3 c.

S

fll'SI [in
the knot

(l

lSUch a
PTOpert)

the 90m

significantly improved creep resistance, and they also displayed stronger
nonlinear rheological behaviors than the un-gelled blends. Because of its
physical nature, the POSS/PDMS gel could be destroyed under large
stain/stress and re-formed under elevated temperatures. The studies of the
POSS chemistry’s effects on the gelation of the POSS/PDMS blends
revealed that associations tended to occur in systems where POSS
macromers were well dispersed in polymer matrix, i.e. where POSS
macromers had good compatibility with polymer. It was also found that the
gelation rates of POSS/PDMS blends increased with raising the annealing
temperatures and the POSS concentrations, and with lowering the PDMS
molecular weights.

In addition, the effects of POSS macromers with different corner
groups on the thermal properties of POSS/PS and POSS/PDMS blends were

also investigated with TGA.

1.2.3 Contributions to the POSS Nana-Technology:

Systematic studies on the POSS/polymer nanO-materials were, for the
first time, conducted in this research work. Contributions Of this work to
the knowledge of POSS Nano-Technology are:

(l) POSS macromers with desired microstructures and properties
(such as: crystallinity, reactivity, solubility, surface property, thermal
property, compatibility with other materials) can be obtained by modifying

the corner groups on the POSS cage.

(2)
mncdnhty
minnble.
Mends ran

nanoscopt:

A
r,’
"J

chemical
massrve
excellent
(4)
POSS/PE
modulus
ccur in

nnatrix. i

It
nanQSCC
lnlEraCI
and int
inleraCI
dlSPEIS
rEQUlre

f“ficrio

(2) Through appropriate functionalization of the POSS cages, the
miscibility between POSS macromer and polymer varies from immiscible to
miscible, and correspondingly, the morphology of the POSS/polymer
blends ranges from complete separation to homogeneous dispersion in the
nanoscopic scale.

(3) POSS macromers with proper reactive corner groups induce
chemical reactions between POSS and polymer. The attachment of POSS
massive cages to polymer chains renders POSS/polymer blends with
excellent heat resistance.

(4) The physical gelation between POSS and PDMS endows the
POSS/PDMS blends with a solid-like behavior. Gelled blends exhibit high
modulus and significantly improved creep resistance. Associations tend to
occur in blends where POSS macromers are well dispersed in polymer

matrix, i.e. where POSS macromers have good compatibility with polymer.

In summary, the crucial factors in developing POSS/polymer
nanoscopic materials with desired properties are the compatibility and
interactions between the two components, which determine the morphology
and interface of the POSS/polymer blends. Good compatibility and strong
interactions between POSS macromer and polymers result in a nano-
dispersed POSS/polymer blend with excellent performance, and these two
requirements may be achieved by selecting POSS macromers with desired

functional corner groups.

To l
Mgh pert
nudying ‘
One clas
polyhedr:
generic t
equal to
sdsesqui
homoger
addnive
mOdtfie:

POlinier

2.1 Ch

“llh ot

DOnd e

SIIOn

(IO

Theref

Chafing

CHAPTER 2

LITERATURE REVIEW

 

 

To meet the challenges for a new generation of lightweight, and
high performance polymeric materials, materials scientists have been
studying the possibility of nanoscale reinforcements for nearly a decade.
One class of compounds potentially suited for such development is
polyhedral Oligomeric Silsesquioxanes (POSS). POSS are compounds with
generic formula (RSiOl.5)n, where R are various hydrocarbons and n is
equal to 6, 8, 10 or higher. Chemically and structurally well-defined
silsesquioxanes can be used as models for silica, as ligands in
homogeneous models for aluminosilicates, silica-supported catalyst, as
additives (such as crosslinking agents, flame retardants, thermal
modifiers, and nano-reinforcing fillers) and as building blocks for

polymers.

2.1 Chemistry of Silsesquioxanes

Second only to carbon, silicon forms the largest number of bonds
with other elements. However, unlike carbon, where C-C, C-0, and C-H
bond energies are approximately equal, the Si-O bond is considerably
stronger than the Si-H bond and much stronger than the Si-Si bond.
Therefore, chains of Si-O-Si-O-Si make up the skeletons of silicate

chemistry.

the fort
sdicate
dunens
therefo

sflicate

are alsr

isconn

2.1.1.4

10 inti
sHsesqr
commo
alOms,
310mg_

for (H5

18005.

hldr01\

Silicates can occur as rings, connected in chains and layers, or in
the form of cages. Among these four types of silicates, the cage structured
silicates compounds represent a rather versatile class of potential three-
dimensional building block units for the synthesis of new materials, and
therefore they are of considerable theoretical and practical interest. Cage
silicates, with a general formula of (XSiOl,5)n, (where n = 6, 8, 10 or
higher: and X can be hydrogen atoms, organic groups or siloxy groups),
are also referred as Sil-ses-quioxanes, which denote that each silicon atom

is connected to three oxygen atoms.

2.1.1 Abbreviations for Silsesquioxanes:

Before discussing the chemistry of Silsesquioxanes, it is necessary
to introduce the notations used to shorten the formulae of the
Silsesquioxanes. In silicates chemistry, M, D, T and Q letters are
commonly used to abbreviate a silicon atom bearing 1, 2, 3, or 4 oxygen
atoms, respectively. Subscripts are used to indicate the number of silicon
atoms, and superscripts to designate the function borne. Examples are TuH

for (HSiOl,5)n, RnTn for (RSiOl_5)n, and Qn for (RR_’R”SiOSiOl,5)n.

2.1.2 Brief History of Silsesquioxanes:
Silsesquioxanes were first synthesized by Ladenburgm in the late
18005. In the early 1900S, Meads and Kipping ”1 investigated the

hydrolysis and condensation reactions of trifunctional silanes and arrived

10

at the C
leads IC
conelusi
underde
Vogt5°
thennal
phenyl
sHsesqu
eafl}' st
functior
T‘
only du
ducoxe

HCCCSS

at the conclusion that polycondensation of “siliconic acids” invariably
leads to extremely complex mixtures with little synthetic value. This
conclusion caused the chemistry of Silsesquioxanes to remain
underdeveloped for a long time. It wasn’t until 1965 that Brown and
Vogtls'm f0und that phenyl oligosilsesquioxanes exhibit remarkable
thermal stability and can be prepared in high yields from readily available
phenyl trichlorosilane. Since then, many stoichiometrically well-defined

[7'9]. However, during the

Silsesquioxane frameworks have been reported
early studies, the majority of known Silsesquioxanes lacked sufficient
functionality for most chemical applications.

The pool Oftknown Silsesquioxane frameworks expanded rapidly
only during the past several years. Some of this expansion is due to the
discovery Of new spontaneous self-assembly reactions that provide ready
access to multi-gram quantities Of several synthetically versatile

Silsesquioxane frameworks “0’ “l

. Another important reason for the rapid
increase in the number of known Silsesquioxane frameworks is the
development of general and highly efficient methodology for synthetically
manipulating both the Si/O core and organic pendant groups on
Silsesquioxane frameworks. Highly functionalized Silsesquioxanes, such

as octaepoxidePOSS, and octapropylPOSS, can be prepared with readily

available octavinylPOSS and the methodology is quite general “2'1“.

11

2.1.3 Strt

The
formula l
silicon at
vertices t

the one c

 

 

cubic sha

the center

Flglll'e

2.1.3 Structure and Classification of Silsesquioxanes:

The structure of cage silicates (Silsesquioxanes), with a general
formula (XSiOl,5)n, is based on Si-O linkages forming a cage with a
silicon atom at each vertex. Substituents (X) coordinate around the silicon
vertices tetrahedrally. The most studied nanobrick for hybrid materials is
the one containing eight silicon atoms (Figure 2.1). It exhibits an almost
cubic shape with one silicon atom at each corner. The oxygen atoms are at
the center of the edges, slightly shifted toward the outside.

X X

 

 

 

 

 

 

 

X can be Hydrogen atoms,
Organic Groups or Siloxy Groups

Figure 2.1 Schematic Diagram of Silsesquioxanes with a Cubic Shape (xssaon).

Within the general formula (XSiOl_5)n, a classification can be made
on the nature of the X groups. They can be hydrogen atoms, leading to the
so-called. polyhedral oligohydridosilsesquioxane (POHSS), which are

commonly abbreviated as Tn". X can also be organic moieties bound to

12

nhcon I
(POSSL
groups 1
rhecage

spherosi

2JJ4 S)
PMyhe

T
ohgohy
exceedi
based .
contair
Water I
UUXIUr
Separa
Only b
numer

pTETCn

SPhEr

“ith R

silicon through a Si-C bond, leading to polyhedral oligosilsesquioxanes
(POSS), which are commonly abbreviated as Tn. Finally, X can be siloxy
groups (RR’R”SiO-). In this last case, the organic moieties are bound to
the cage framework through Si-O-Si links and those nanobricks are named

spherosilicates, which are commonly abbreviated as Q“.

2.1.4 Synthesis of Silsesquioxanes:
Polyhedral Oligohydridosisesquioxane (POHSS) T..":

The first report on the preparation of a polyhedral
oligohydridosilsesquioxane (Hssisoiz) was made in 1959 with the
exceedingly small yield of 0.2%.“51 In 1991, Agaskar proposed a method
based on a biphasic reaction medium (HClaq, methanol, hexane, toluene)
containing Fer.““ In such a medium, HSiC13 is slowly hydrolyzed by the
water released from the partially hydrated iron salt. This synthesis leads to a
mixture of T3" and T10", yields being 17.5% and ~8%, respectively after
separation and purification. The other Tn" compounds (n=12, 14, 16, 18) can
only be prepared with very low yields ~1%, and need to be separated through
numerous and complex steps. Those low yields likely explain the

preferential use of T3" in hybrid materials.
Spherosilicates On:

The synthesis of compounds following the formula (RMeZSiOSiOl,5)n,

with R: H, CH3, CH=CH2, CHZCH=CH2 and CHZCl, has been proposed in the

13

lucrature
(05101 sl'

Sp?
atleast 2:”
by treatir
good yie'

proposet

The dram
To“ corn
reactions

Th
((lSi()15
b6 prepp
hydrolyz
the form”
ammonia

S:
{TOUT SP
Vari0u5
Slnrhes.

metal a‘

 

literature from the oligohydrido (HSiOl,5)n, or from the polyanions,
(OSi01.s)n "1

Spherosilicates can be prepared by reacting the T...H compounds with
at least 2n equivalents of Me3NOClSiMe2R, this reagent being first obtained
by treating ClSiMezR with anhydrous Me3NO.“7‘ ‘81 This reaction offers
good yields of at least 50%. The need for Zn equivalents has allowed to
propose the following mechanism:

(HSiOl,5)n +Me3NOClSiMe2R —>
(RMeZSiOSiOLg)n + nMe3NClSiMe2R + nMe3NOHCl
The drawback of this method, however, is that the reaction starts from the
TnH compounds whose syntheses strongly reduce the overall yield of the
reactions.

The other synthetic route uses as precursors the polyanions
(OSiOl,5)n“‘, which exhibits the same cage structure. These compounds can
be prepared with very good yields from aqueous silicate solutions or by
hydrolyzing Si(OCH3)4 under basic conditions.“9' 20] In both cases, to favor
the formation of the cage structures, the key point is the use of quaternary
ammonium as charge compensating cations.

Spherosilicates with more complex functions can also be prepared
from simple ones (R: H, vinyl...). As an example, the hydrosilylation of
various unsaturated compounds by (HMeZSiOSiOl,5)3 has allowed to
synthesize nanobricks bearing epoxy function, trimethoxysilanes groups, or

metal alkoxides moieties through the complexation by a B—ketoester. [2" 22]

14

Polyhed

Tl
skeleton
hydrolyt
where F
reactive
oligosil:
RSiY; l

equatior

H
complic

formati

the COn
Characr
EYOUp 3
rate of
POlyhe(
above-l
dlfflCu]
are Ver

Polyhedral Oligomeric Silsesquioxanes (POSS) T..:

The most common process used to obtain polyhedral silicon-oxygen
skeletons of oligosilsesquioxanes with R as an organic group is by the
hydrolytic condensation of trifunctional organosilicon monomers RSiY3,
where R is a chemically stable organic substituent and Y is a highly
reactive substituent, such as C1, or alkoxy. The formation of
oligosilsesquioxanes in the course of hydrolytic polycondensation of
RSiY3 monomers in dilute solvents can be represented by the overall
equation:

nRSiY3 + 1.5n H20 W (meow), +3nHY

However, in reality the above reaction is a multistep and rather
complicated process. The hydrolysis of RSiY; involves the consecutive
' formation of linear, cyclic, polycyclic, and finally polyhedral siloxanells].

The reaction above is strongly dependent of many factors, such as:
the concentration of initial monomer in the solution; nature of the solvent;
character of substituent R in the initial monomer; nature of functional
group Y in the initial monomer; the type of catalyst employed, temperature,
rate of addition of water and quantity of water added; and solubility of the
polyhedral oligomers formed. Because of the strong mutual effects of the
above-mentioned factors, the precise polycondensation process is very
difficult to predict. The products of hydrolytic polycondensation of RSiY3
are very complicated. It is a mixture of fully condensed silsesquioxanes,

incompletely condensed silsesquioxanes and resins (Figure 2.2)[23].

15

I)

,\ /( )r I R\ _

H\

:ocoaom octagon—392°.— osbohcml Mammy— .ue 32:5...— xo-QEoU "Wu 953m

moWV lav/Wain” v. M? .Ewomé.
\—

_ _ lol. _ o/ \o\_m/oi*I
lav W. m\ a” H? \__/_ aw

o~m+ roam

 

 

 

 

l6

Experims

the desit

1. Eu
ln
cquivale
complete
cycloher
as Vin}
oridizec

Variety t.

V)

\
Si “

h,
3‘63

 

Experimental conditions have to be optimized to favor the formation of

the desired silsesquioxane product.

1. Fully Condensed Silsesquioxanes:

In general, fully condensed POSS systems (Figure 2.3) contain
equivalent organic groups on each silicon atom, rendering them either
completely functionalized with stable groups, for example, the
cyclohexyls in Cyng, or fully functionalized with reactive groups, such
as Vinylng [24’ 25]. Fully functionalized POSS can be chlorinated [9],

[26, 27]

oxidized to Spherosilicates , or treated with olefins to produce a

[28-29] .

variety of hydrosilylation products

 

 

R10T10
Figure 2. 3: Examples of Fully Condensed POSS Systems

2. Incompletely Condensed Silsesquioxanes:
Incompletely condensed silsesquioxane frameworks (Figure 2.4)

have attracted a great deal of attention. The reactivity of the silanol

17

I
group5
models

alumino:

I
COnden

 

 

famine
addlll‘i

agents.

 

groups makes the incompletely condensed POSS system of interest as

[30-34]

models for silica as ligands in homogeneous models for

[35-39]

aluminosilicates and silica supported catalysts [4°43]. Incompletely

 

 

 

 

 

 

R
R7T4D3(0H)3

R
R8T6D2(OH)2

 

0;. we

Rs/ 0
t. .. 0th
l/

31—— OH R
R R3T2D4(OH)4 R41,4(OH)4

 

 

Figure 2. 4: Exampr of Incompletely Condensed POSS Systems

condensed silsesquioxane systems are also very useful precursors to new
families of graftable or polymerizable macromers that can be utilized as
additives for polymers (for example: crosslinking agents, nano-reinforcing

agents, and thermal modifiers) and for the preparation of POSS-based

18

var
frar

unti

be pi
of al
h)drc
monoi

OllgOS

polymeric systems. For example, the trisilanol functionality of the
R7T4D3(OH)3 structure (Figure 2. 5 ) can be corner capped with various
silane coupling agents, which contain organic groups suitable for
polymerization, to produce fully condensed T3 POSS compounds with
controlled functionality. Through variation of the Y group on the silane, a

Y
i OC/ i

£414.

R

 

T—OH
R OH

LO.—

 

P\F

.2 at
/ 1:

R7T4D3(0H)3

 

 

 

 

 

 

 

R7T8Y

Figure 2. 5: Corner Capping of R7T4D3(OH)3.

variety Of functionalities can be placed off the corner of the POSS
framework. Subsequent transformations of this group can be carried out
until the desired functionality has been obtained.

A variety of incompletely condensed silsesquioxane frameworks can
be prepared in synthetically useful quantities via hydrolytic condensations
of alkyl- or aryltrichlorosilanes (Figure 2. 6). In most cases, however,
hydrolytic condensation reactions of trifunctional organosilicon
monomers afford complex resins and/or fully condensed

oligosilsesquioxanes, rather than incompletely-condensed frameworks.

19

R

o} l

R R OH

Acetone/H20 / l] /_/

RSiCl3 + '1 /\Sr $1

)5 pa

R: O I{3i 0 S'\

R

Figure 2. 6: Incompletely Condensed Silsesquioxane Prepared by the

Hydrolytic Condensation of (c-C6H11)SiCl3.

 

 

 

\.

 

Recently, the discovery that a single Si-O-Si linkage in a fully condensed
framework can be cleaved selectively by strong acids or base (e.g. HBF4/BF3,
TfOH, and Et4NOH) provides an important method for preparing many useful
incompletely condensed frameworks ”4’5”. For example: Rgsigojz (R=c-C6Hn)
reacts selectively with aqueous Et4NOH to afford discrete incompletely
condensed silsesquioxanes: it first produce R38130|1(OH)2, which reacts further

with EtaNOH to produce R7Si709(OH)3 (Figure 2. 7).

- . R S' o o
a. R38i3012 b418518011“)le C 7 l7 9( H)3

Base=Et4NOH, R: 0
Figure 2. 7: Base-mediated Cleavage of Fully Condensed [C5H11)3Si3012]

thrc

con
oitl

hyb

2.2.

poly
poly
with
the r
desir
macn

term

and c

mpg]>

2.2 Polymeric Materials Containing POSS

POSS macromers can be incorporated into polymeric systems
through two techniques:

1) Hybrid Polymers containing POSS: POSS macromers, which
contain functional organic reactive sites, can polymerize or copolymerize
with other organic species to produce a variety of organic-inorganic
hybrid homopolymers or copolymers.

2) POSS/Polymer Nanoscopic Blends: POSS macromers, used as
nano-reinforcing agents, blend with polymers to produce

inorganic/organic nanoscopic materials.

2.2.1 Organic-Inorganic Hybrid Polymers Containing POSS

POSS macromers can be polymerized using a standard
polymerization protocol (i.e. radical polymerizations, condensation
polymerizations, ring opening polymerizations etc.) to provide polymers
with a variety of architectures as illustrated in Figure 2. 8. Depending on
the type of functionality contained on the POSS macromers and on the
desired polymer architecture, POSS macromers can be introduced into
macromolecular systems as either a main chain, side chain, or as chain
terminus groups [52].

Several POSS homopolymers and copolymers have been synthesized
and characterized, for example: POSS-Styryl based homopolymers and

[53-56]

copolymers , methacrylates-POSS polymers [57' 58], norboryl- POSS

21

cops

sho‘
POE
gror
p01:

pha

[59] [60.]

copolymers , POSS-siloxane copolymers , POSS-epoxy polymers

[61, 62] [63. 64]

, POSS—polyurethane copolymers , etc. (some examples are

shown in Figures 2.9, 2.10, 2.11 and 2.12). The property studies of these
POSS containing polymers showed that because the massive inorganic
groups (i.e. POSS cages) are attached to polymer chains, the POSS-
polymer chains act like nanoscale reinforcing fibers or like a hard block

phase separated from a soft block, producing enhanced heat resistance [53'

55.58.61.631 [55.59.61]

and mechanical properties

22

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

38m

whoa—Eon vow

2.32 .3 9:53.293 5 .N 2:»:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

e835

 

23

 

R

. 0 /R D

 

 

(c-C6H11)7Si8012PmPyl Methacrylate

R
(POSSMA) POSS-Me thacrylate Hormpolylmr
(poly-POSSMA)
T": T":
O
M c_cH l_HH_ m

hf hi

Vii—l . 1:... '°"’
"Ll“ " n; “/1

POSS-MetlncrylatelMetlncr-ylate Copolymr

Figure 2. 9: Polymerization of Methacrylates-POSS Homopolymer
and Copolymer

24

Frau

Me‘Si 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 2.11: POSS-Siloxane Copolymer

25

>._._(4 5W2:

.. Ml. 3°“ _... ..
l" —.{C| . + iii—“2 tel.”
f—°_l .. sooc

 

POSS-Epoxy Propolymer

 

 

Poss-Remote“! Epoxy Resin

Figure 2.12: Schematic of the Curing Cycle of the POSS-
Epoxy System

26

2.2.2

POS

into

{Cr}
and
com
film
and
blen
les'e
unbl
char
tran
ther
POE
bler
incr
I0 rt
Cnh;

ll'le .

2.2.2 POSS/Polymer Nano-Materials:

Currently there are few literatures concerning the investigation of
POSS/polymer nano-materials, where POSS macromers are incorporated
into polymer by blending. Only a couple of papers are found so far.

Lichtenhan, Noel, Bolf and Ruth [57] blended (C6H5)6Si609,
(C6H5)3813012, and Acrylic-POSS macromer with PMMA at 3, 6, 9, 12, 15,
and 30% (w/w) level. Acrylic-POSS macromer showed better
compatibility with PMMA than the other two POSS macromers. Clear
films were obtained only at 3 and 6% loading levels for the (C6H5)6Si609,
and (C6H5)gSi3012 macromers. But Acrylic-POSS macromer / PMMA
blends were clear throughout the 3-30% loading range. At 3-6% loading
levels the TGA and DSC traces were observed to be similar to those of
unblended PMMA in terms of the onset temperature Of decomposition,
char yield, and glass transition. This suggests that despite their
transparency and apparent homogeneity there was no significant effect on
thermal properties and little if any interaction between the PMMA and the
POSS macromers. The visible phase-separated 15% and higher loaded
blends with (C6H5)(,Si609, and (C5H5)3SlgO]2 showed a modest 5-10°C
increase in glass transition by DSC over unblended PMMA, which is due
to the POSS rich surface layer on the samples rather than a true property
enhancement. Char yields were observed to be higher in blends containing

the Acrylic-POSS macromer.

27

p0l}PI(
shear !
crystal
POSS

concen
indicat
OIIWDS
sheara
thatth
during
crossl
chains
chains

addiu

blend
Olun
key j
delel

llalTOn

[65] studied the crystallization of isotactic

Fu, Yang, Somani, etc.
polypropylene (iPP) containing nanostructured POSS at quiescent and
shear state. It was observed that the addition of POSS increased the
crystallization rate of iPP at quiescent condition, which suggests that
POSS crystals act as nucleating agents. However, at 30wt% POSS
concentration, the crystallization rate was significantly reduced,
indicating a retarded growth mechanism due to the molecular dispersion
of POSS in the matrix. In situ SAXS was used to examine the behavior of
shear-induced crystallization of the POSS/PP blends. The results showed
that the addition of POSS significantly increased the crystallization rate
during shear. The authors postulate that POSS molecules behave as weak
crosslinkers in polymer melts and increase the relaxation time of iPP
chains after shear. Therefore, the overall orientation of the polymer
chains is improved and a faster crystallization rate is obtained with the
addition of POSS.

Because the combining of POSS macromers with polymer by
blending is a new approach to achieve nanO-materials, there are still a lot
of unknown domains that need to be investigated for this technique. The
key issue in this field is to develop POSS Nano-Technology, i.e. to

develop new design principles that allow to control POSS macromers at

nanometer level and to achieve effective POSS-polymer interface.

28

PART I

INVESTIGATIONS OF POSS MACROMERS

29

ll

3d lnl

opport

thennc

the hi
inuiat
POSS;
relaUc
S}'Sl€n

consn

CHAPTER 3

STRUCTURE-PROPERTY STUDIES OF
POSS MACROMERS

 

'— -————— w—‘m v ——

3.1 Introduction

The recent development of POSS macromers affords a tremendous
opportunity for the preparation of new polymers (thermoset,
thermoplastics, and elastomers) and new polymeric blends. As part of our
ongoing effort to investigate, understand, and develop these materials as a
new class of nano-reinforcing fillers for polymers, an investigation into
the morphology and thermal properties of these POSS macromers was
initiated. This study is essential to optimizing the processing of the
POSS/Polymer blends, and for understanding the structure-property
relationships of the blends, since any given property of a multi-component
system is some (more or less complex) function of the properties of the
constituents and of the interactions between them.

In the following chapter, the morphology and thermal properties of
the POSS macromers were examined, using X-ray diffraction, Differential
Scanning Calorimetry (DSC), and Thermogravimeric Analysis (TGA),
with special emphasis given to the effects of the organic corner groups on
the POSS cages. We expect that the chemistry of the corner groups affect
the degree of the orderly packing of the POSS cages, the transition

temperatures, and the thermal stabilities of the POSS macromers.

3O

'3
I‘D

diff

L”
1.)

C13

b.)
I.)

tarp

“as

[he

3.2 Experimental
3.2.1. POSS Macromers:

POSS Macromers used in this study so far are all T3 cages bearing
different corner groups. These POSS macromers were obtained from
Hybrid Plastics Corporation. Their chemical formulae, structures,
abbreviations and molecular weight (M.W.) are shown in Table 3.1 and

Figure 3.1.

3.2.2 Sample Preparations:
3.2.2.1 Samples Preparations for Differential Scanning Calorimeter
(DSC), and Thermogravimetric Analysis (TGA):
POSS powders were used directlyfor DSC, and TGA tests.
3.2.2.2 Samples Preparations for X-Ray Diffraction:
POSS macromers were dissolved in toluene for 12 hours; solvent

evaporated and the samples dried under vacuum for 12 hours at 60°C.

3.2.3 Characterization Techniques:
3.2.3.1 X-ray Diffraction:

Measurements were performed using a Scintag XRD 2000 with a Cu
target; 20 angle ranged from 5° to 30°; Step size and scan rate used here
was 003° and 2° lmin, respectively.

The x-ray diffraction pattern obtained from a diffractometer records

the X-ray intensity as a function of diffraction angle. The inter-atomic

31

 

 

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32

 

 

 

Cp3 POSS

Cyg POSS

OD \ss.
/- t.

:/\/@ StyrenylgPOSS

PthOSS

R = —< IsobugPOSS

R ___ J V3POSS

Figure 3.1: POSS Macromers With Different Corner Groups (cont’d)

33

 

 

 

 

Y: —@/\ ST 1Cp7POSS
/\/@ Styrenyl 1CP7POSS
Y: \

// V1Cp7 POSS

C He C POSS
Y: /\/<:> y 1 p7

Y: STllsobu7POSS

Figure 3. l: cont’d

spacing t5

 

on

ray (l.=l.

3.2.3.2 E

Tr
a Mettle
a [low

tempera

3.3 x

diff“

fTOm

spacing is determined by Bragg’s law:
d = n l. / (23in9)
Where (1 is the inter-atomic spacing; A is the wavelength of the x-

ray (1:1.5406A for Cu target); 0 is the diffraction angle.

3.2.3.2 Determination of Transition Temperatures of POSS macromers:
Transition temperatures of POSS macromers were determined using

a Mettler-Toledo 821e/400 Differential Scanning Calorimeter (DSC) under

a flow of nitrogen and with a heating rate of 10°C/min. The transition

temperature is taken as the maximum peak position of the transition peak.

3.2.3.3 Thermal Stability:

Thermogravimetric analysis(TGA) was carried out on a Hi-Res TGA
2950 under Nitrogen atmosphere. Temperature range used was 25 to
600°C; Heating rate utilized was 20°C/min. Decomposition Temperature
Tdec is taken as the temperature where 5% weight loss occurred. Residue

is the weight percent of the sample remains after the TGA test.

3.3 X-Ray Crystallographic Analysis of POSS Macromers
To examine the microstructures of POSS macromers, X-Ray
diffraction analysis was performed. The X-ray diffraction pattern obtained

from a diffractometer records the X-ray intensity as a function of the

35

diliractiot
packing 0
The

of corner

3.3.1 Eff

Fig
macromc
diffracttt
the diffr.

Cc
CPsPOS‘.
34). Pit.
3~7l mat
macrom.
macmm
macrom

diffract;

SpaClng
micron

ViPOS.‘

 

diffraction angle 20, and it gives the information about the orderly
packing of the molecules in crystals.
The studies below mainly focused on the impacts of different kinds

of corner groups on the microstructures of the POSS macromers.

3.3.1 Effects of POSS Corner Groups:

Figures 3.2 to 3.13 show the X-ray diffraction curves of POSS
macromers bearing different corner groups. And their corresponding
diffraction data (peak positions, inter-atomic spacing, and the 29 width of
the diffraction peaks) are listed in Table 3.2

Comparing the X-ray curves of all the RgPOSS macromers:-
CngOSS (Figure 3.2), CngOSS (Figure 3.3), StyrenylgPOSS (Figure
3.4), PthOSS (Figure 3.5), VgPOSS (Figure 3.6) and IsobusPOSS (Figure
3.7) macromers, it can be seen that CngOSS, CngOSS and Isobu3POSS
macromers have more sharp peaks than PthOSS and StyrenylgPOSS
macromers. Only some weak and broad peaks are found in PthOSS
macromer, and StyrenylgPOSS macromer has only one weak peak in its
diffraction pattern.

Comparing the ~8°29 diffraction peak of all the RgPOSS
macromers, it can be seen that VgPOSS macromer has the smallest d-
spacing (9.0A. see in Table 3.2), which is due to the fact that the VgPOSS
macromer has eight small vinyl groups. The high regularity of the

VgPOSS macromer allows a close packing of the POSS cages. CngOSS

36

1.6E

HE

.213

1

0E

SDI

1:3:—

6.01

4.0]

10‘.

0.0

a)

5.

NJ.
5725::

 

1.6E+05 ,
1.4E+05 8'2
1.2E+05

1.0E+05

y

8.0E+04

Intensit

19.1

6.0E+04

4.0E+04

 

 

 

2.0E+04

 

0.0E+OO n

 

2 0
Figure 3.2: X-ray Diffraction Profile of CngOSS Macromer

 

4.0E+05
3.5E+05 -: 7-3
3.0E+05 ah

2.5E+05 -

 

ITWrVTTj II

Intensity

2.0E+05 «g
1.5E+05 ~§

1.0E+05 i

 

5.0E+04 i

 

 

 

o.ora+oo ”

 

Figure 3.3: X-ray Diffraction Profile of CngOSS Macromer

37

5.015:
45E-
4.0E
3.5E

p.»
O
m

Intensity
[J
J
m

r.)
O
r-r1

8.0l

v.0.“
no.0

Intensit
4‘ Y
A

1.1

0.1

 

isos+04
1L5E+04
ztdE+04
:r5E+04
Egsrnsuyt 853
'gza55+04
rszaos+04
LSEHon '
rins+04
5,013+03

(roE+oo . 1 . 1 1 r . 1 . . . . . . . . . . . . i , . . , .
5 10 15 20 25 30
2t)

 

 

Figure 3.4: X-ray Diffraction Profile of StyrenylgPOSS Macromer

 

8.0E+04 _

‘10E+04-E
(sos+04-£
:50E+04-E
‘LOE+04-E

y

  
 
 
  
 
 

Intensit

C
3.0E+O4 -:

2.0E+O4 —:

 

 

 

1 .OE+O4

 

0.0E+00 .
5 10 15

Figure 3.5: X-ray Diffraction Profile of PhsPOSS Macromer

38

7.0E+04

 

6.0E-t-04
9.8

5.0E+04

nty

4.0E+04

Intens

3.0E+04

22.9
23.7

2.0E+04

 

13.1 21.1

 

 

1 .0E+04

 

0.0E+00 e1 1 e t 1 1 1 * t 1 . e 1+ #4 . lfil . e 1 e r
5 10 15 20 25 30
28

 

Figure 3.6: X-ray Diffraction Profile of V3POSS Macromer

 

5.0E+06 p a
4.5E+06
4.0E+06
3.5E+06 E
Z,3.01«:+06
E 2.5E+06
5 2.0E+O6
1.5E+06 ~.
1.0E+06 E
5.0E+05 E
0.0E+00 ’

7.6

 

 

 

 

 

1' ti

T

 

3-7 15.7
I 23.8 25.7
10 15 20 2

5 30
29

Figure 3.7: X-ray Diffraction Profile of IsobugPOSS Macromer

39

 

rsOE+O4 ,

5105+04-f

ztdE+04-{ 8‘3

1105+04~§
~ urz

Intensity

 

220E+04-E 11

:LOEaO4-f

 

 

 

(105+oo ' 1 . 1 . t . . 1 1 t 1 . ... , . . . . +..
5 10 15 20 25 30
211

Figure 3.8: X-ray Diffraction Profile of STleyPOSS Macromer

 

6.0E+04

snea044

19.2
4.0E+04 -

Intensrty
93

zoen04- '19

1.0E+04

 

 

 

(1m 1 1 1 1 1T 1 1 1 1 lfi 1 L 1 1 l 1 1 1 1 l
29

Figure 3.9: X-ray Diffraction Profile of Styrenylle7POSS Macromer

4o

 

Intensrty
:-- rJ N s»
L)! O J O

1.0E-

5.01:-
l

oor

Intensity
) _L.

 

 

5.013+04
4.51=.+04
4.013+04
3.5E+04
3.0E+04
E 2,513+04
'5 2.013+04 .
1.5E+04
1.01=.+04
5.0E+03

00E+mlllllll#Lil414ill441l

5 10 15 2 9 20 25 30

7.7

Slty

18.6 19.3

11.2

 

 

 

Figure 3.10: X-ray Diffraction Profile of CyHele7POSS Macromer

 

8.0E+04

7.0E+04

6.0E+04

5.0E+O4

1ty

4.0E+O4

 

Intens

3.0E+O4

18.5

 

2.0E+04 4;

   

1.013+04 —E

 

 

 

p—
1 1 L 1 I 1 L 1 1 1 J i l 1 I .1 1 1 I 4 1
ODE-FOO I I r I

5 10 15 20 25 30
2 9

Figure 3.11: X-ray Diffraction Profile of VleyPOSS Macromer

41

 

5.0E+O4
4.5E-104 4
4.0E+04 4
3.5E-104 a

I

Intensrty
N 9°

2.0E+04
1.5E+04 4
1.0E+04 ~
5.0E+03 -

 

0.0E+(X)

7.7

18.5

 

 

29

Figure 3. 12: X-ray Diffraction Profile of STllsobu7POSS Macromer

6.0E+04

 

5.0E+O4 4

4.0E+04 ~

3.0E+04 ~

Intensity

2.0E+04 -

1.0E+04 -

 

0.0E+(X)

7.6

8.3

11.5

I

1

1 1

19.4

 

 

5

10

I
1

L
r

15

29

1
l

20 25 30

Figure 3. l3: X-ray Diffraction Profile of Styrenylllsobu-IPOSS Macromer

42

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43

8?.

h:

and CngOSS macromers have similar X-ray curves, however, CngOSS
has larger d-spacing (Table 3.2) than CngOSS, which is probably
introduced by the additional methylene unit in the cyclohexyl group.
StyrenylgPOSS macromer is the least ordered macromer among all the
R3POSS macromers, which is due to its huge and rigid corner group.

The replacement of one corner group (R) in the RgPOSS macromers
with a different chemical group alters the morphology of the POSS
macromers. Comparing the X-ray curves of STlCP7POSS (Figure 3.8),
Styrenylle7POSS (Figure 3.9), CyHelCP7POSS (Figure 3.10), and
V.Cp7POSS (Figure 3.11) macromers with the diffraction curve of the
CngOSS (Figure 3.2) macromer, we observed that ST|Cp7POSS,
StyrenyIICp7POSS, CyHeICP7POSS, and V1Cp7POSS macromers have
fewer and less sharp peaks than CngOSS, indicating that ST1Cp7POSS,
Styreny11Cp7POSS, CyHe1CP7POSS, and Vle7POSS macromers are less
ordered than CngOSS macromer. This is because that the introduction of
one styryl / styrenyl/ cyclohexenyl/or vinyl group into CngOSS reduces
the symmetry and regularity of the POSS cage structure, and hence
hinders the close packing of ST1Cp7POSS, Styrenthp7POSS,
VICp-IPOSS and CyHe1CP7POSS macromers. The same results are also
observed in the X-ray diffraction patterns of STllsobu7POSS (Figure
3.11), Styrenylllsobu7POSS (Figure 3.12), in comparison with the X-ray

diffraction of IsobusPOSS macromer (Figure 3.6).

The above discussion is only a simple comparison of the structures
of POSS macromer with different corner groups. A complete
crystallographic analysis of theses POSS macromers is beyond the scope

of this work and will be the subject of a future research.

3.3.2 Summary:

The chemistry of the corner groups on the POSS cage affects the
morphological structures of the POSS macromers. The higher the
symmetry and regularity of the POSS macromers, and the smaller the size
of the corner groups, the more ordered the POSS macromers.

Among the 12 POSS macromers investigated, CngOSS, CngOSS,
VsPOSS, and IsobugPOSS are more ordered than PthOSS,
StyrenylgPOSS, ST1Cp7POSS, Styrenyl1Cp7POSS, CyHele-IPOSS,

V1Cp7POSS, STllsobu-IPOSS and Styrenylllsobu7POSS.

3.4 Thermal Stabilities of POSS Macromers
Thermal stability studies on the POSS macromers bearing different
corner groups were conducted. This type of information provides insight
into the understanding of the thermal stabilities of POSS/Polymer blends.
In this experiment, Thermogravimeric Analysis (TGA) is used to
determine the decomposition temperature (Tdec), and weight loss (or

residue) of the POSS macromers.

45

the dec
the Tdc
as the
bonds.
inorga
molec
chenn

loss

whicl
of 45
klhn
(abo
kJ/n
size
316.
P()S
[her

are

Thermal stability of a matter can be embodied by two parameters:
the decomposition temperature (Tdcc) and weight loss. The magnitude of
the Tdcc is mainly determined by the chemical structure of the matter, such
as the bond energy, defects inside the molecule and reactivity of the
bonds. Weight loss is decided by the content of organic elements and
inorganic elements in the molecules, and whether there are more stable
molecules formed during the decomposition pathway as a result of a
chemical reaction. The higher the carbon element, the larger the weight
loss.

POSS macromers are composed of a silica-like inorganic core,
which is surrounded by organic groups. The Si-O bond has a bond energy
of 451 kJ/mole, which is higher than the bond energy of the C-C (345

[66]. However, the bond energy of Si-C

kJ/mole) in organic materials
(about 318 kJ/mole) is much lower than the bond energy of Si-O (451
kJ/mole), and the bond energies of Si-alkyl bonds become smaller as the
size of the alkyl group is increased. For example, the bond energies of Si-
Me, Si-Et, and Si-Pr are 331, 211, 192 kJ/mole respectivelyl66]. Because
POSS macromers consist of both organic and inorganic components,
therefore, it is expected that the thermal stabilities of POSS macromers

are primarily influenced by the stabilities of the organic corner groups on

the POSS cage.

46

0‘.

l:

3.4.1 Effects of POSS Corner Groups:

Figures 3.14 to 3.25 show the TGA curves of POSS macromers with
different corner groups. The values of the Tdec, weight loss, and residues
of these POSS macromers, which are obtained from their TGA curves are
tabulated in Table 3.3. Table 3.4 lists the molecular weight of the POSS
macromers, their weight percentages of the inorganic Si-O portion, and
the organic C-H portion.
3.4.1.1 Decomposition Temperatures (Tdcc) of POSS Macromers:

During the TGA experiments, the decomposition temperature (Tdec)
is taken as the temperature where 5% weight loss occurred. It can be seen
from Figures 3.14 to 3.25' that the order of the Tdcc of POSS macromers
from high to low is: PthOSS (487.97°C, Figure 3.17), StyrenylgPOSS
(458.18°C, Figure 3.16), CngOSS (397.5°C, Figure 3.15), STICp-IPOSS
(381.22°C, Figure 3.20), Styrenthp7POSS (374.62°C, Figure 3.21),
CngOSS (371.56°C, Figure 3.14), V1Cp7POSS (369.05°C, Figure 3.22),
CyHeICp7POSS (348.14°C, Figure 3.23), StyrenyllIsobu7POSS (301.2°C,
Figure 3.25), STllsobu7POSS (284.96°C, Figure 3.24), IsobugPOSS
(267.58°C, Figure 3.18), and V3POSS (251.28°C, Figure 3.19). It is
noticed that this sequence is nearly the same as the sequence of the
molecular weight of these POSS macromers from high to low as shown in
Table 3.4, except for CyHe1Cp7POSS macromer.

Comparing the TGA curves of all the R3POSS macromers (Figure 3.

26), we can see that PthOSS (487.97°C) and StyrenylgPOSS (458.2°C)

47

macro
macro
moder

(lilj

Wu
re;
My

101

macromers have significantly higher Tdec than the other R3POSS
macromers. CngOSS (397.5°C) and CngOSS (37l.56°C) macromers have
moderate thermal stabilities. ISObUgPOSS (267.58°C), and V3POSS
(251.28°C) have the lowest Tdec among all the R3POSS macromers.

We also observed that POSS macromers containing vinyl /or
isobutyl corner groups have relatively low Tdec, for example: Vle7POSS
(369.05°C), Styrenylllsobu7POSS (301.2°C), STIIsobu7POSS (284.96°C),
ISObUgPOSS (267.58°C), and V3POSS (251.28°C).

Comparing the Tdcc of STle7POSS, Styrenylle7POSS,
CyHele7POSS, and V1Cp7POSS macromers with that of CngOSS
(Figure 3.27), we can see that the replacement of one cyclopentyl with
styryl increases the Tdec by about 10°C (STleyPOSS), while, the Tdec of
CngOSS decreases by 23°C when replacing one of its cyclopentyl groups
with cyclohexenyl group (CyHele7POSS). Styrenylle7POSS and
Vle7POSS macromers have nearly the same Tm,c as CngOSS macromer.

By comparing the Tdcc of STIIsobu-IPOSS and Styrenylllsobu7POSS
with that of IsobusPOSS macromer (Figure 3.28), it can be seen that the
replacements of one isobutyl group in IsobugPOSS with styryl group and
styrenyl group increase the Tdec by 17°C (for STllsobu7POSS), and 34°C
for (Styrenylllsobu7POSS).

The above results showed that the chemistry of the corner groups on
the POSS cages significantly affected the thermal stabilities of the POSS

macromers. As stated in the beginning of this section, the Tdec

48

 

120

 

 

 

 

 

 

 

 

 

 
 
  
 
  
    

 

 

100 371 .56°C 95.00%
80-
°33 94.35%
5,60 (4.720mg)
'5
3
40*
Residue:
20- 5.644%
(0.2824mg)
x—Jt
o . . . . r I r u . u
100 200 300 400 500 600
Temperature (°C)
Figure 3. l4: TGA curve of CngOSS Macromer
120
4
100 397.50°C 95.00%
80-
;? 85.28%
2.’ (4.947mg)
560-
d)
g i
40“ Residue:
14.73%
436.80°C 23.72% 0.8543mg)
.4
20 506.54°C 20.46% L
0 Y ' ' r I ' I ‘ r
100 200 300 400 500 600

Temperature (°C)

Figure3. 15: TGA curve of CngOSS Macromer

49

 

 

120

 

 

 

 

 

 

 

 

 

    

100 20.88% '
458.18°C 95.00% .498mg)

80-
Q Residue:
O
:7 79.12%
560‘ (9.466mg)
(D
3

40-

J
20-
o . . . , . . . f . ,
1 00 200 300 400 500 600
Temperature (°C)
Figure 3. 16: TGA Curve of StyrenylgPOSS Macromer
120
100 \
487.97°C 95.00%
80-

 

Weight (%)
c»
‘3

 

 

Residue:
404 52.71%
J (9.800mg)
20
0 . , Y , . , . r . r
1 00 200 300 400 500 600

Temperature (°C)

Figure 3. l7: TGA Curve of PhsPOSS Macromer

50

 

A0\ov «50.0;

120

 

100

 

Weight (%)
-k 0) on
C? e <?

N
9

 

267.58°C 95.00%

  
   
 
 
 
 
    

94.64%
(15.23mg)

305.84°C 38.89%

369.77°C 29.50%
Residue:
5.357%
(0.8623mg) L

 

f

 

0
100

120

260 360 .. 460 ' 560 ' 600
Temperature (°C)

Figure 3. 18: TGA Curve of IsobugPOSS Macromer

 

100

 

a:
O
A; 1

Weight (%)
O)
‘7’

 

251 28°C 95.00%

52.13%
(5.187mg)

 

 

 

40‘ Residue:
47.87%
(4.763mg)
20*
1
o T r I ' r r r ' I
100 200 300 400 500 600

Temperature (°C)
Figure 3. 19: TGA Curve of V3POSS Macromer

51

 

 

11

Ao\ov 398))

AAYOV ~£C~mv>>

120

 

100

 

(D
‘3

Weight (%)
O)
‘?

 

 

   
 
 
 
  

381 22°C 95.00%

60.19%
(4.372mg)

521 .89°C 50.09%

 

 

 

 

 

    
 

4o~ i
Residue:
39.80%
20. (2.891 mg)
0 ' ' I I r v r
100 200 300 500 600
Temperature (°C)
Figure 3. 20: TGA Curve of STle-IOSS Macromer
120
100
374.62°C 95.00%
80‘ 67.66%
(6.41 1 mg)

Weight (%)
a:
‘?

 

 
 
  
  

465.53°C 53.35%

 

 

 

40‘ 535.59°C 43.79% L
Residue:
20- 32.32%
(3.062mg)
0 T . , . j . , . ,
100 200 300 400 500 600

Temperature (°C)

Figure 3. 21: TGA Curve of StyrenthpyPOSS Macromer

52

 

'T

120

 

100'

0
8

O
6
Ao\ov 30.0))

(

4

1X.» .ccmcxs

 

 

 

  
   
  
      

 

 

 

 

 

  
  
 
  
  

 

 

10° 348.14°C 95mm
1
801
\°
E: i 96.07%
560‘ (6.554mg)
0
3
405
Residue:
20- 3.931 °/o
393.91 °C 14.63% (0-2682m9)
0 454.48°C 10.66% L
100 200 300 400 500 600
Temperature (°C)
Figure 3. 22: TGA Curve of CyHele7POSS Macromer
120
100
369.05°C 95.00%
80
§
: 79.51%
3601 (9.650mg)
0 4
3 40 412.96°C 47.52%
471 .68°C 40.52%
20‘ Residue: L
20.50%
0 (2.488mg)
100 200 300 400 500 600

Temperature (°C)
Figure 3. 23: TGA Curve of VleyPOSS Macromer

53

 

 

A665 «:90; l 1 A66» E305

120

 

 

   
   
  
    

 

 

 

 

 

 

   
  
  
    

 

 

 

 

‘00 284.96°C 95.00%
801
8: 89.50%
.. 7.708m
@607 ( 9)
0)
3
4 2
0 Residue:
10.50%
20- (0.9043mg)
L
o . . . . 2 . . h . .
100 200 300 400 500 600
Temperature (°C)
Figure 3. 24: TGA Curve of STllsobu7POSS Macromer
120
1
‘00 301.20°C 95.00%
801
g 1
.360. 96.450/0
.5 (17.23mg)
; 1
401
Residue:
2° 3.605%
(0.6437mg) L
0 . , . f . , - , . ,
100 200 300 400 500 600

Temperature (°C)

Figure 3. 25 : TGA Curve of Styrenylllsobu-IPOSS Macromer

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57

Table 3.3: Thermal Stabilities of POSS Macromers
with different Comer Groups (TGA results)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

POSS Df§&gi%lq WEIGHT RESIDUE
Macromers . o CHANGE (%) (%)
(at 5% Welght Loss, C)
CngOSS 371.5 94.35 5.644
CngOSS 397.5 85.28 14.73
StyrenylgPOSS 458.1 20.88 79.12
PthOSS 487.9 47.29 52.71
ISObUgPOSS 267.5 94.64 5.36
V3POSS 251.2 52.13 47.87
STICPyPOSS 381.2 60.19 39.8
Styrenthp7POSS 374.6 67.66 32.32
CyHele7POSS 348.1 96.07 3.93
VICp7POSS 369.0 79.51 20.49
STIIsobu7POSS 284.9 89.50 10.50
Styrenyl 1 Isobu7POSS 301.2 96.45 3.6

 

 

 

 

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59

magn

such

bond

Ihel

mdh

ch61

POE

magnitude of a material is mainly determined by its chemical structure,
such as the bond energy, defects inside the molecule and reactivity of the
bonds. The degradation of POSS macromers starts from initial cleavage of
the C-C and Si-C bonds in the corner groups. The above TGA results
indicate the C-C and Si-C bond energies on the POSS cages vary with the
chemistry of the corner groups. The more stable the corner groups on the
POSS cage, the higher the Tdec of POSS macromer. The order of thermal
stabilities of the organic groups from high to low is: Phenethyl, Styryl,
Styrenyl, Cyclohexyl, Cyclopentyl, Isobutyl, Vinyl and Cyclohexenyl

groups.

3.4.1.2 Residues of the POSS Macromers:

Residue of the POSS macromers is taken as the weight percentage
of the sample remains after the TGA test. We can see from Table 3.3 that
the order of the POSS residue yields from high to low is: StyrenylgPOSS
(79.12wt%), PthOSS (59.7lwt%), V3POSS (47.87wt%), STICp-IPOSS
(39.80wt%), StyrenyIICp7POSS (32.32wt%), V1Cp7POSS (20.50wt%)
CngOSS (l4.73wt%), STIIsobu7POSS (10.50wt%), CngOSS (5.64wt%),
Isobu8POSS (5.36wt%), CyHe1Cp7POSS (3.93wt%), and
StyrenylllsomeOSS (3.6wt%).

Among all the RgPOSS macromers (Figure 3.26), POSS macromers
containing benzene rings and/or double bonds in their corner groups have

higher residue yields. For example, the residues of the StyrenylgPOSS

60

are l

Sty

exl

res
PC

8']

(79.12wt%), PthOSS (52.7lwt%), and V3POSS (47.87wt%) macromers
are higher than those of the CngOSS (l4.73wt%), CngOSS (5.64wt%),
and Isobu3POSS (5.36wt%). Comparing the residues of the CngOSS,
CngOSS and IsobugPOSS macromers, we can see that the larger the mass
of the corner groups on the POSS cage, the higher their residue yield: the
residue of the CngOSS macromer (l4.73wt%) is higher than those of
CngOSS (5.644wt%) and Isobu3POSS (5.36wt%) macromers.

As shown in Figure 3.27, the STICp7POSS (39.80wt%),
Styreny11Cp7POSS (32.32wt%) and V1Cp7POSS (20.50wt%) macromers
exhibit significantly increased residue yields when compared with
CngOSS (5.64wt%), while, CyHe1Cp7POSS (3.93wt%) displays a lower
residue than CngOSS (5.64wt%). However, we didn’t see this trend in the
POSS macromers containing isobutyl groups (Figure 3.28): the residues of
STIIsobu7POSS (10.50wt%) and Styrenylllsobu7POSS (3.6wt%) are about
in the same order as IsobusPOSS (5.36wt%).

The above results showed that the chemistry of POSS has
considerable impacts on the residue yields of the POSS macromers. As
stated earlier, the residue of a matter is decided by the content of organic
elements and inorganic elements in the molecules, and if there are more
stable molecules formed during the decomposition pathway as a result of a
chemical reaction. This principle also applies to POSS macromers. As

shown in Table 3.4, the weight percentages of the inorganic Si-O cages in

61

mePOS
ofmec

h
PMPOS
nmmer
inorgan
rauhs
reports
memu

PMPOF

U98?
macro:
M me
{CSpec
mar.
m65§
M PC

chemr’

H4];

Stylef

 

the POSS macromers are between 33~65wt%, depending on the chemistry
of the corner groups.

It is noticeable in Table 3.4 that StyrenylgPOSS (79.12wt%) and
PthOSS (52.7lwt%) macromers have considerably high residues. We
notice that these values are higher than the weight percentages of their
inorganic Si-O (~33wt%) content. Based on this fact and also on the
results that the loss of POSS cages takes place around 450 to 600°C, as

[67], we postulate that at high temperatures

reported by Mantz, Jones, etc
chemical crosslinking reactions might occur in the StyrenylgPOSS and
PthOSS macormers that results in the formation POSS resin.

As seen in Table 3.4, the residue yields of the STICp7POSS
(39.82wt%), Styrenylle7POSS (32.32wt%) and VgPOSS (47.87wt%)
macromers are similar to or somewhat lower than the weight percentages
of their inorganic Si-O content: 41.51wt%, 41.51wt%, and 65.82wt%
respectively. We presume that in these POSS macromers, partial losses of
their organic corner groups and also their inorganic Si-O cages occur in
the systems; and the experimental fact that there are still some remaining
of POSS macromers even at temperatures above 450°C is because
chemical reactions might take place among some of the POSS cages.

Table 3.4 also reveals that V1Cp7POSS (20.5wt%), CngOSS
(14.73wt%), STIIsobu7POSS (6.24wt%), CngOSS (5.64wt%),

ISObUgPOSS (5.36wt%), CyHeICp7POSS (3.93wt%), and

Styrenylllsobu7POSS (3.6wt%) macromers have very low residues

62

 

(3~30
Iheiri
in the
clear
res'rd

resrd

3.4.1

is H

NO

Crr
lso
C}'
an
Sl

EX

Pr

(3~20wt%). These values are much lower than the weight percentages of
their inorganic Si-O cages (40~45wt%), indicating that most of Si-O cages
in these POSS macromers are lost during the heating. However, it is not
clear why STIIsobu7POSS and Styrenylllsobu7POSS have very low
residues, while, STle7POSS, and Styrenylle7POSS have very high

residues.

3.4.1.3 Two Mass-Loss Regions:

Another feature noticed in the TGA curves of the POSS macromers
is that during the decomposition process, some POSS macromers display
two mass-loss regions.

Two clear mass-loss regions are observed in the TGA curves of
CngOSS (350-436°C, and 506-550°C, as shown in Figure 3.15),
IsobugPOSS (250-300°C, and 370-450°C, as shown in Figure 3.18),
CyHele7POSS (BSD-410°C, and 470-600°C, as shown in Figure 3.22),
and Vle7POSS (300-400°C, and 450-500°C, as shown in Figure 3. 23).
STIprPOSS (Figure 3. 20), and Styrenylle7POSS (Figure 3. 21) also
exhibit two mass-loss regions, but less distinctive.

The presence of two mass-loss regions suggests that the above
POSS macromers have more complicated thermal decomposing processes

than other POSS macromers.

63

The mechanism of POSS decomposition, which can be developed by
analyzing the gas-phase product and chars of the samples, is beyond the
scope of this research. More detail studies on the thermolysis of POSS

macromers can be found in references [59-61].

3.4.2 Summary:

The chemistry of the organic corner groups on the POSS cages
plays an important role in determining the thermal stabilities of POSS
macromers. The POSS macromers with functionalities, which may
undergo chemical crosslinking reactions, possess high thermal stability,
for example: StyrenylgPOSS and PthOSS macromers. Among all the 12
POSS macromers investigated, the StyrenylgPOSS (Tdec: 458.18°C,
Residue: 79.12wt%) and PthOSS (Tdec: 487.97°C, Residue: 52.71wt%)
macromers have significantly high decomposition temperatures and
residues.

The order of the POSS decomposition temperature from high to low
is: PthOSS (487.97°C), StyrenylgPOSS (458.18°C), CySPOSS (397.5°C),
STle7POSS (381.22°C), Styrenylle7POSS (374.62°C), CpsPOSS
(371.56OC), VICp7POSS (369.05°C), CyHele7POSS (348.14°C),
Styrenylllsobu7POSS (301.2°C), STlIsobu7POSS (284.96°C), IsobusPOSS

(267.58°C), and V8Poss (251.28°C).

The order of the POSS residue yields from high to low is:

StyrenylgPOSS (79.12wt%), PhSPOSS (59.71wt%), VSPOSS (47.87wt%),

64

ST

(IE

3.5

ire
Ti

[6!

STle7POSS (39.80wt%), Styrenylle7POSS (32.32wt%), Vle7POSS
(20.50wt%), Cy8POSS (14.73wt%), STIIsobu7POSS (10.50wt%), Cp8POSS
(5.64wt%), IsobusPOSS (5.36wt%), CyHele7POSS (3.93wt%), and

Styrenylllsobu7POSS (3.6wt%).

3.5 Transition Temperatures of POSS Macromers
3.5.1 Effects of POSS Corner Groups:

Differential Scanning Calorimetry (DSC) was used to test the
transition temperatures of POSS macromers with different corner groups.
The DSC results are showed in Figures 3.29 to 3.40, and the transition
temperature data are listed in Table 3.5. Some of these transitions shown
in the DSC figures are the fusions of POSS crystalline structures, and
some of them are the destruction of POSS weak associations. The heats of
these fusions or disassociations of POSS macromers are very weak
(between 2~4OJ/g), except that VgPOSS has a relatively high heat of
fusion, which is about 135.4J/g.

We can see that the CngOSS (Figures 3.29), StyrenylgPOSS
(Figure 3.32), and IsobusPOSS (Figure 3.34) macromers all have two
transition peaks: 12.5°C (disassociation) and 29.9°C (disassociation) for
CngOSS; 189.1°C (disassociation) and 274.3°C (melting) for
StyrenylgPOSS; and 496°C (disassociation) and 272.1°C (melting) for
IsobusPOSS. The disassociation temperatures of the CngOSS and

PthOSS macromers are 23.7°C and 765°C, respectively. VgPOSS,

65

 

0.5 i

g)

C

Heat of Flow (J/
b

:L
M
1

1
N

{11

 

— Cp8POSS

llllllllllllllllllllllllllllllll l l l l 1 l

 

 

 

Figure 3.29: DSC Curve of CngOSS Macromer

 

(Hg)

,6:

,b

Heat of Flow
as

I
y—s
p—a

1

7 V T

. —Cy8Poss

 

 

 

.L.
O
O 1 r

 

1111111411
I i

llllll11%14LL411111#11L1%11J1+14L1

150 2(1) 250 300 350 400 450
Tarpa'ature (°C)

Figure 3.30: DSC Curve of CngOSS Macromer

50 1(1)

66

 

 

 

 

 

 

 

 

 

 

 

 

 

E — Styreny18POSS
0.5 «E J
A oi 2.2?
g: i
3 _05 _f 189.10C
o .
E :
2 -1 t 274.3°c
£3 :
-1.5 «E
-2 .
_25 F 1 m1 1 111111111111m111111111111111111111111
0 50 100 150 200 250 300 350 400 450
Temperature (°C)
Figure 3.31: DSC Curve of StyrenylgPOSS Macromer
1 : _
’ —""P118POSS
ng J;
D :
3 :
o :
E: :
«— c
3 2i
8 ' E 765°C
”—2.5 i
-3
-35
.4 U111HHrwwrwuewawwwrl”I11H[will
0 50 100 150 200 250 300 350 400 450

Temperature (°C)
Figure 3.32: DSC Curve of PthOSS Macromer

67

 

— V8POSS

0.5 (E

O
1

Heat of Flow (J/g)

 

.6:
Vi

 

 

 

O 50 100 150 200 250 300 350 400 450
Terrperature (° C)

Figure 3.33: DSC Curve of V3POSS Macromer

 

—- Isobu8POSS

 

J
TJITYITTITI

_b
u:

496°C

Heat of Flow (J/g)

I
t—d .
Lit r—-
l l

272. 1°C

 

 

-25 LLllllllllrlllJ‘LrillllllllliiLJ+Lgl+llJl+1lll
0 50 100 150 200 250 300 350 400 450
Tenperature (°C)
Figure 3.34: DSC Curve of IsobugPOSS Macromer

 

68

 

i —ST1Cp7POSS

Heat of glow (J/g)
{ll

 

 

 

 

0 50 100 150 2(X) 250 3(X) 350 400 450

Tenpaature (° C)

Figure 3.35 : DSC Curve of STleqPOSS Macromer

 

1.5

0.5 -:

Heat of Flow (J/g)
b
LII

l
H .
U! H
l 1
I I I I I I

 

 

—— Styrenylle7POSS

 

 

11111 1111114444111111411l11111111111111111411
T I I I I I I I

50 100 150 200 250 300 350 400 450
Temperature (°C)

Figure 3.36: DSC Curve of Styrenthp7POSS Macromer

69

 

 

 

 

 

 

 

 

 

 

 

 

i —CyHe1Cp7POSS
0.7 f
20.2 4
2° C
O .
3 ,
o-0. ‘
u- : r
0
gas ~-
-1.3
’ 339.1°C
-131111++le~~+uwlfilw*1”PLHIHrHHIfHU
0 50 100 150 200 250 300 350 400 450
Temperature(°C)
Figure 3.37: DSC Curve of CyHele7POSS Macromer
1
—V1Cp7POSS
0.5 -
t
3:0 i-
'3
3
O
E
H—
O
‘5
O)
I:
-2“Hr“LL11H*+‘*+LHIH+U"Hillrlluriw+
0 50 100 150 200 250 300 350 400 450
Temperature(°C)

Figure 3.38: DSC Curve of V1Cp7POSS Macromer

70

 

 

o E 229°C

Heat of Flow (J/g)

1
N
1

1.x)
0
1
IITT_ITIIIIIIII IIITI II

 

— STlIsobu7POSS

 

 

..
11111H11111111111111111111111111111111
- . Fl I I I I I I

0 50 100 150 200 250 300 350
Temperature (° C)

Figure 3.39: DSC Curve of STlIsobu7POSS Macromer

 

 

 

 

 

l
E — Styrenylllsobu7POSS
0.5 i
3" i
D 0:
.3 Li
U4 _
“5 r
3* —O.5 4:
m .
E
-1 _-
“ 169.30C
-15hLl111111Lf 1 L11L1I111T 1111111++¥L111111
0 50 100 150 200 250 300 350 400 450

Temperature (° C)

Figure 3.40: DSC Curve of Styrenylllsobu7POSS Macromer

71

Table 3.5: Transition Temperatures of POSS Macromers (DSC Results)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

POSS TransitigaTemperature Heat of (Bisiociation
Macromers 1 2 l g 2
CngOSS 12.5 29.9 4.4 6.2
CngOSS 23.7 ~ 2.5 ~
StyrenylgPOSS 189.1 274.3 4.5 29.6
PthOSS 76.5 ~ 37.8 ~
IsobusPOSS 49.6 272.1 14.6 10.2
V3POSS 349.1 ~ 135.4 ~
Styrenyl lCmOSS ~ ~ ~ ~
STle7POSS ~ ~ ~ ~
CyHele7POSS 339.1 ~ 15.9 ~
VleyOSS ~ ~ ~ ~
Styrenylllsobu7POSS 169.3 ~ 22.0 ~
STlIsobu7POSS ~ ~ ~ ~

 

 

 

 

 

 

 

CyHele7POSS and StyrenylllsomeOSS macromers have a melting
temperature at 349.1°C, 339.1°C and 169.3°C respectively. It is also
noticed that the melting temperatures of ISObUgPOSS (Figure 3.34),
CyHe1Cp7POSS (Figure 3.37), and Styrenylllsobu7POSS (Figure 3.40) are
very close to their decomposition zones.

No transition peaks were found in STle-IPOSS (Figure 3.34),
Styrenylle7POSS (Figure 3.36), Vle7POSS (Figure 3.38), and
STlIsobu7POSS (Figure 3.39) macromers. However, both ST1Cp7POSS
and STlIsobu7POSS macromers have one upward peak, at 160°C and

229°C respectively, which indicates that an exothermal reaction takes

place during heating.

72

Only the melting transitions of V3POSS, IsobusPOSS,
StyrenylgPOSS, and CyHeleyPOSS macromers are observed in the DSC
experiments. Even thought the melting peaks of CngOSS, CngOSS,
PthOSS, Styrenylle7POSS, STle7POSS, V1Cp7POSS, and
STlIsobu7POSS macromers are not observed in their DSC curves, we
assume that it is because that their melting temperatures are higher than
their decomposition temperatures. The small disassociation peaks found in
CngOSS, CngOSS, Styreny18POSS, PthOSS, and IsobugPOSS
macromers are thought to be a destruction of weak aggregations in these

POSS macromers.

3.5.2 Summary:

The melting temperatures of StyrenylgPOSS, IsobusPOSS, VgPOSS,
CyHele7POSS and Styrenylllsobu7POSS macromers are 274.3°C,
272.1°C, 349.1°C, 339.1°C and 169.3°C, respectively. The melting peaks
of CngOSS, CngOSS, PthOSS, Styrenylle7POSS, STle7POSS,
Vle7POSS, and STlIsobU7POSS macromers are not observed because
their melting temperatures are higher than their decomposition
temperatures. STle7POSS and STlIsobu7POSS macromers have one
upward peak, at 160°C and 229°C respectively, which indicates that an
exothermal reaction takes place during heating.

Weak associations are observed in CngOSS, CngOSS,

Styreny18POSS, PthOSS, and IsobusPOSS macromers.

73

PART II

INVESTIGATIONS OF POSS/POLYMER BLENDS

74

PREFACE

The following two chapters describe a study where POSS
macromers were incorporated by mixing into traditional polymers to
prepare POSS/Polymer blends. Two kinds of polymers were used.
Polystyrene (PS), one of most commonly used thermoplastics, was
selected as one of the model polymers. Another one, chosen from
polysiloxane polymers, was Polydimethyl Siloxane (PDMS).

Compared to other inorganic fillers, POSS macromers possess
greater potential as a nano-reinforcing filler. As stated in Chapter 1,
POSS macromers have two unique features. First, the chemical
composition is a hybrid: POSS macromers have an inorganic silica-like
core, which is surrounded by organic groups. The organic groups
surrounding the POSS framework can be made to be compatible with
polymers to form blends of nano-reinforced blends. Second, the physical

size of POSS macromers is about 1.5 nm [I]

, which is nearly equivalent in
size to most polymer segments and coils. Because of these two
characteristics of POSS macromers, it is expected that nano-dispersed
POSS/polymer blends can be fabricated for nearly every type of polymer
matrix by modifying the chemistry of the corner groups.

The following research is intended to answer the question of how

POSS macromers can be “molecularly” dispersed in polymer matrix to

75

 

 

form

S1IUC1

 

itisc

two Cr

 

morp
homc
mor;
para
inte
fum
bet‘
con

dis

(IQ

Prr
“h
an

1h.

form a nanoscopic material, and to determine what are the
structure/property relationships of the POSS/polymer blends.

In general, in order to achieve the optimum performance of a blend,
it is crucial that its morphology of the blends and interface between the
two components be carefully controlled.

The morphology of a blend plays a key role in determining its
properties. Both the response to an applied mechanical stress and the
physical properties exhibited by the blend will depend markedly on its
morphology, such as: the amount of phase separation, the sample
homogeneity, and the domain size in a phase-separated system. The
morphological structure of a multi-component blend is affected by many
parameters, such as the complex interplay of rheology, diffusion,
interfacial forces and time-scale of processing. However, the decisive
fundamental factor in determining its morphology is the compatibility
between the components. With increasing compatibility between its
components, the morphology of a blend becomes more homogeneously
dispersion.

The interfaces between the two components in a blend also have a
significant influence on the performance of the material. Mechanical
properties in filled systems are limited by the strength of the interface,
which is often the weakest element of a blend. A favorable chemical
and/or physical interaction between the two constituents usually enhances

the mechanical properties of the blend.

76

Because of the above reasons, an investigation on the morphology
and interaction between POSS and polymeric matrix was initiated. TEM
and X-ray diffractometer were utilized to characterize the morphologies
of the POSS/polymer blends. The interactions between POSS macromers
and polymers were analyzed by monitoring the changes of the glass
transitions of the polymer chains, which were detected by DSC.

An examination of the performance of POSS/polymer blends was
followed after their morphology studies. Properties investigated in this
paper included thermal stability and rheological properties. Thermal
stability is one of the important advantages that organic materials can
obtain by combining with inorganic materials. TGA was employed to test
the thermal stability of the POSS/polymer blends. The interaction between
POSS with varying organic groups and polymer matrix was examined
using rheological techniques, which were carried out with a Universal
Dynamic Spectrometer. Because of the limited quantities of POSS
materials, only the rheological properties of POSS/PDMS blends were
conducted.

Based on the above morphology and performance studies of the
POSS/polymer blends, we generated the structure and property

relationships of the blends.

77

 

 

I!

blen

infll

Cor.

SIUI

CO‘1

CHAPTER 4

MORPHOLOGY, INTERACTION
AND THERMAL STABILITY STUDIES
OF POSS/POLYSTYRENE (PS) BLENDS

 

 

4.1 Introduction:

The morphology, interaction and thermal stability of POSS/PS
blends were investigated. The studies were mainly focused on the
influence of POSS chemistry on the morphologies of the POSS/PS blends.

Polystyrene (PS) is one of the most commonly used thermoplastics.
Composed of only carbon and hydrogen atoms, PS is a good model for
studying the effects of POSS macromers bearing different organic corner
groups on the compatibilities, and hence the morphologies, of the blends.
In this study, TEM was utilized to characterize the morphologies of the
POSS/PS blends, and X-ray diffractometer was employed to identify the
morphological changes of POSS macromers after they were blended with
PS. It is expected that POSS macromers, which have less crystallinity and
bear organic corner groups chemically similar to PS, will be more
compatible with PS and hence more homogeneously dispersed in the PS
matrix.

The interactions between POSS macromers and PS were analyzed by
monitoring the changes of polymer glass transition, which were detected

by DSC. It is thought that because there are no strong interaction forces

78

 

bar

1101

the

$13

between POSS macromers and PS, the molecular mobility of PS chains is
not much affected by the addition of POSS macromers.

Because of the limited quantities of POSS macromers, only the
thermal stability of the POSS/PS blends was conducted. Thermal

stabilities of the POSS/PS blends were characterized by TGA.

4.2 Experimental:
4.2.1. Materials:
4.2.1.1 Polystyrene (PS):

Monodispersed PS was obtained from Aldrich Chemical Company.
PSZM: Mw=2316000, PSZK. Mw=216,000.

Poly-dispersed PS (PSlM: Mw=1,600,00, Mw/Mn S 1.16) was
purchased from Pressure Chemical.
4.2.1.2 POSS Macromers:

POSS Macromers used for the experiments described in this chapter
included CngOSS, CngOSS, StyrenylgPOSS, PthOSS, IsobusPOSS,
VgPOSS, STle7POSS, Styreny11Cp7POSS, CyHele7POSS, V1Cp7POSS,
STlIsobu7POSS, and Styrenylllsobu7POSS. Their chemical structures are
illustrated in Table 3.1 and Figure 3.1.

POSS Loadings in PS were 20wt%, 50wt%, and 80wt%.

4.2.2 Sample Preparations:

4.2.2.1 Transmission Electron Microscope (TEM) Samples Preparation:

79

PS and POSS macromer were dissolve in THF for more than 4
hours. The concentration of the solution was approximately 0.5%. The
solution was then dropped onto a glass slide and let to dry in the air. The
film was removed from the glass slide by slowly immersing the slide into
a vessel of water at a 45° angle to the surface. Next, the grids were
dropped onto the film and the whole piece of film with grids on the
surface was lifted out of the water using a section a paper. The grids were
dried on filter paper and subsequently carbon coated to increase their
beam stability.
4.2.2.2 Samples Preparations for Differential Scanning Calorimeter
(DSC), Thermogravimetric Analysis (TGA) and X-Ray Diffraction:

Preparations of POSS/PS blends were performed by dissolving PS
and POSS macromer in toluene for 12 hours; evaporating the solvent, and

then by drying the samples under vacuum for more than 12 hours at 60°C.

4.2.3 Characterization Techniques:
4.2.3.1 Transmission Electron Microscope (TEM):

Thin films were observed on JEOL 100CX TEM using an
acceleration voltage of 120kv.
4.2.3.2 X-ray Diffraction:

Measurements were performed using a Scintag XRD 2000 with a Cu
target; 20 angle ranged from 5° to 30°; Step size and scan rate used here

was 0.03° and 2° /min, respectively.

80

 

the ‘

spac

W h

The x-ray diffraction pattern obtained from a diffractometer records
the X-ray intensity as a function of diffraction angle. The inter-atomic
spacing is determined by Bragg’s law:

d = n). / (23in0)
Where (1 is the inter-atomic spacing; I. is the wavelength of the x-ray
(1:1.5406A for Cu target); 0 is the diffraction angle.
4.2.3.3 Thermal Stability:

Thermogravimetric analysis was carried out on a Hi-Res TGA 2950
under Nitrogen atmosphere. Temperature range used was 25 to 600°C;
Heating rate utilized was 20°C/min. Tdec is taken as the temperature where
5% weight loss occurred. Residue is the weight percent of the sample
remains after the TGA test.
4.2.3.4 Determination of Glass Transition Temperature (Tg):

Glass transitions were determined using a Mettler-Toledo 821e/400
Differential Scanning Calorimeter (DSC) under a flow of nitrogen and
with a heating rate of 10°C/min. The glass transition temperature was
taken as the inflection point of the glass transition region. The glass
transition width is the temperature span between the onset of the

transition and the endset of the transition.

81

4.3

£th

 

ble

fur

4.3 Morphological Studies of POSS/PS Blends By Transmission
Electronic Microscope (TEM)

This section presents the morphological structures of POSS/PS
blends observed by TEM. We have investigated the effects of different
functionalized POSS macromers, POSS concentration, and molecular

weights of PS on the morphological structures of the blends.

4.3.1 Effects of POSS Macromers with Different Corner Groups on the
Morphologies of POSS/PS2M Blends (50wt% POSS Loading):

Figures 4.1 to 4.8 show the TEM photographs of blends of PSZM
with CngOSS, STICp7POSS, StyrenylgPOSS, PthOSS, CngOSS,
V3POSS, CyHele7POSS and V1Cp7POSS (POSS Loading: 50wt%; PS
molecular weight: 2316000). The phase characteristics of these blends are
summarized in Table 4.1.

As shown in Figure 4.1, the CngOSS/PSZM blend has two phases
with PS as the continuous phase and snowflake like CngOSS
macromers as the disperse phase. The dimensions of the CngOSS
aggregates are around 140-2000nm. The replacement of one cyclopentyl
group with one styryl group (STle7POSS) changes the pattern and the
dimensions of the POSS aggregates. STGC7POSS aggregates in
ST1Cp7POSS IPS2M blends are roughly round shape, and their sizes are

approximately 70-600nm (Figure 4.2). Because of the less crystallinity

82

Table 4. 1: Phase Characteristics of the POSSIPSZM Blends (50 wt% POSS)

 

 

 

 

POSS/PS2M Phases Continuous Dispersion Dimensions of the
(50 wt%) Phase Phase dispersron phase
CngOSS Two PS POSS 140—2000nm
CngOSS Two PS POSS microns

StyrenylgPOSS Two POSS+PS PS 50-200nm

 

PthOSS One ~ ~ ~

 

 

 

 

VgPOSS Two PS POSS microns
ST1Cp7POSS Two PS POSS 70-600nm

CyHele7POSSH Two POSS+PS POSS+PS microns

V1Cp7POSS Two PS POSS microns

 

 

 

 

 

 

 

83

...
...... ......

..
r

.
.

......
..

.
..

5......
N:

 

TEM Image of CpsPOSSIPSZM Blend (50 wt% POSS)

.1

Figure 4

 

POSS)

TEM Image of STle7POSS/PS2M Blend (50 wt%

Figure 4. 2

84

of thc

and S

 

I
increa

enhan~

 

mar
l .

1111

dis

3111

of the ST1Cp7POSS, and also the more chemical similarity between PS
and ST1Cp7POSS, the introduction of one styryl group into CngOSS
increases the compatibility between ST1Cp7POSS and PS, and therefore,

enhances the dispersion of the POSS macromer.

 

Figure 4. 3: TEM Image of StyrenylgPOSSIPSZM Blend (50 wt% POSS)

The substitution of all the cyclopentyl groups in the CngOSS
macromer with styrenyl groups (StyrenylgPOSS) renders a phase inversion
in the Styreny18POSS/PSZM blend: PS (white round particles) becomes the
disperse phase, and the continuous phase is a mixture of StyrenylgPOSS

and PS (Figure 4.3).

85

11W

:3

 

Figure 4. 4: TEM Image of PthOSS/PSZM Blend (50 wt% POSS)

The replacement of all the cyclopentyl groups in CngOSS
macromer with phenethyl groups dramatically improves the compatibility
between PthOSS and PS. The PthOSS macromer is homogeneously
dispersed in the PS matrix. There is no phase separation in the
PthOSS/PSZM blend (Figure 4.4).

Phase separations are observed in CngOSS/PS2M (Figure 4.5),
VgPOSS/PSZM (Figure 4.6), CyHe1Cp7POSS IPSZM (Figure 4.7) and
V1Cp7POSS IPSZM (Figure 4.8) blends, with POSS being the disperse
phase, PS as the continuous phase. The dimensions of POSS aggregates in

these blends are in the range of microns (Table 4.1).

86

 

Figure 4. 6: TEM Image of VgPOSS/PSZM Blend (50 wt% POSS)

87

 

Figure 4. 8: TEM Image of V1Cp7POSS/PS2M Blend (50 wt% POSS)

88

 

 

4.3.'

Bier

Sty

PS

for

DC

4.3.2 Effects of POSS Loading on the Morphologies of POSS/PS2M
Blends:

The morphologies of the blends of PSZM with CngOSS, CngOSS,
StyrenylgPOSS, PthOSS, VgPOSS, and ST1Cp7POSS (20wt% POSS loading,
PS molecular weight: 2316000) are displayed in Figures 4.9 to 4.14.

As with the 50wt% PthOSS/PSZM blend, no phase separation is
found in the 20wt% PthOSS/PSZM blend. Yet, phase separations still
occur in the 20wt% POSS loading blends of CngOSS/PSZM (Figure 4.9),
CngOSS/PSZM (Figure 4.10), StyrenylgPOSS/PSZM (Figure 4.11),
VgPOSS/PSZM (Figure 4.13), and ST1Cp7POSS/P82M (Figure 4.14).
However, compared to the 50wt% blends, POSS macromers in the 20wt%
blends are more homogeneously dispersed and the phase boundaries are
less distinctive. This effect is a consequence associated with the kinetics
of the phase separation, which occurs during the TEM sample preparation
process. During this process, when POSS macromers and PS have only a
limited compatibility, the POSS macromers tend to aggregate and phase-
separate from the PS matrix to form their own phase. As the PS content is
increased, more PS molecules present in the system hinder the POSS
macromers from migrating towards each other, leading to a decrease in
the diffusion rate of the POSS macromers. Therefore, POSS macromers in
the low POSS loading POSS/PS blends are more homogeneously dispersed
in the PS matrix than those in the high POSS loading

blends. After the solvent evaporates, POSS clusters are frozen in the PS matrix.

89

‘ .1 J
M":

(”Int

-1
It",

 

Figure 4. 9: TEM Image of CngOSS/PSZM Blend (20 wt%)

 

Figure 4. 10: TEM Irmge of CngOSS/PSZM Blend (20 wt%)

90

 

Figure 4. ll: TEM Image of StyrenylsPOSS/PSZM (20 wt%)

 

Figure 4. 12:TEM Image of PthOSS/PSZM Blend (20 wt%)

91

 

TEM Image of VgPOSS/PSZM Blend (20 wt%)

Figure 4. 13

..:_...

.
.

”ML“... .

...

... .

......

.2...

......
W5.
..

.....s.
K.._».

......
...:t:

......

.... ......3...
:22...

.
.... _

 

)

TEM Image of STleyPOSSIPSZM Blend (20 wt%

. 14:

4

gure

Fi

92

4.3.3 Effects of PS Molecular Weight on the Morphologies of

PhsPOSS/PS Blends:

 

Figure 4. 15: TEM Image of PthOSS/P8216K Blend (20 wt%)

The morphological structure of the PthOSS/PSZI6K blend (20wt%
POSS loading; PS molecular weight: 216,000) is shown in Figure 4.15.
The TEM image reveals that phase separation occurs in the PthOSS/PS
blend with a low molecular weight PS. From a thermodynamic point of
view, in a given composition at a particular temperature, reducing the
molecular weight of the polymer enhances the miscibility between the
POSS and the polymer, which should lead to a more homogeneously

dispersed POSS phase. However, the morphology of a blend also depends

93

on the rheology of the components. Based on kinetic theory consideration,
if the components of a blend are not truly miscible at the molecular level,
phase separation will occur faster in the low molecular weight (low
viscosity) matrix than in the high molecular weight matrix (high
viscosity). Therefore, a two-phase structure appears in the low molecular
weight blend: PthOSS/PSZI6K. While a single-phase structure is formed

in the high molecular weight blend: PthOSS/PSZM.

4.3.4 Discussion:

The morphology of a blend depends on the compatibility between
the two components, the type of molecular interaction and the resultant
interface, the rheology of the components and the processing history.

For POSS/Polymer blends, the following factors influence the
compatibility between the two components, and hence the morphologies of
the blends:

1. The chemistry of POSS: The chemical structures of the corner groups
on the POSS cage greatly influence the compatibility between POSS
and polymers.

The above studies showed that the compatibilities between POSS
and PS varied with different POSS chemical structures. Notably,
among the eight POSS macromers studied, the PthOSS macromer is
the most compatible one with PS and, hence, it is the one which can

be homogenously dispersed in the PS matrix.

94

The degree of the crystallinity of POSS macromers also affects the
morphologies of the POSS/PS blends. The potential for achieving
miscible blends in which one or both components are crystalline is
low because of the heat of fusion which would have to be overcome to
achieve the necessary thermodynamic criteria for mixing. High
crystallinity POSS does not favor the formation of homogeneous
dispersion of the POSS. POSS macromers with a strong tendency to
crystallize are inclined to aggregate and phase separate from the
polymer host.

. Composition of the mixture: The above TEM results showed that the
low POSS loading blends have a more homogeneously dispersed POSS
phase than the high POSS loading blends. This is because with
increasing polymer content, more polymer chains interfere with the
migration of the POSS macromers, leading to a more homogeneity of
the blends.

. The molecular weight of the polymer: In a given composition at a
particular temperature, from a thermodynamic view, reducing the
molecular weight of polymer enhances the miscibility between POSS
and the polymer. However, the morphology of a blend is also affected
by the rheology of the components. Kinetically, because the viscosity
of the polymer drops with a decrease of its molecular weight, POSS
macromers are more easily to aggregate in low molecular weight

matrix during the sample preparation process, especially when the two

95

components are not truly miscible at the molecular level. Therefore,
phase separation of the components occurs relatively easily in the low

molecular weight polymer blends.

4.3.5 Summary:

The chemistry of POSS macromers plays an important role in
determining the morphologies of the POSS/PS blends. Depending on the
attached chemical groups on the POSS macromer, the morphologies of
POSS/PS blends ranged from a complete phase separation between POSS
and PS to a homogeneous dispersion of POSS in the PS matrix in a
nanoscopic scale. Among the eight POSS macromers used, PthOSS is the
most compatible one with P8 and can be homogeneously dispersed in PS
matrix. All other POSS/PS blends display a certain amount of phase
separation to a various degrees.

The POSS concentration and PS molecular weight also influence the
morphologies of the POSS/PS blends. With a decrease of POSS loading
and increasing of PS molecular weight, POSS macromers are more

homogeneously dispersed in the PS matrix.

4.4 X-Ray Crystallographic Analysis of POSS/PS Blends
In this section, X-ray diffraction techniques were employed to
characterize the morphologies of POSS/PS blends. The effects of the PS

on the crystalline structures of POSS macromers were studied by

96

comparing the X-ray diffraction patterns of the POSS macromers in the

POSS/PS blends with those of the neat POSS macromers. The results

reflect the degree of compatibility between the POSS macromers and PS.
In the X-ray curve, the crystallography of a matter is characterized

by the positions and the 20 widths of the diffraction peaks.

4.4.1 Effects of POSS Chemistry and POSS Loading:

Figure 4.16 shows the X-ray diffraction curves of CngOSS macromer
and CngOSS/PSZM blends (20 and 50wt% POSS loading). The numbers in
the plot are the 29 positions of the peaks. Their respective d-spacing and 20
width are listed in Table 4.2. Comparing the X-ray curve of CngOSS
macromer with that of the 50wt% POSS loading blend, we can see that

there are two well-defined crystalline peaks in CngOSS macromer,

 

L6E+05 .
—:— Cp8POSS
—Cp8POSS/PS(20/80)

6 6 ' Cp8POSS/PS(50/50)

L4E+05“E

1.2E+05 ‘

I T r1 Tj’T
_—

1.0E+05 ‘E L

ty

 

8.0E+04 4 1.5
18.8

Intensi

 

vuw

 

4.0E'l'04 F"! ‘ii'.l1figa§*ffi‘ilk “fl
aw: “ ' W“*‘7fi*k#qwn£“
2.0E+O4 '

 

0.0E+00r - . 3-21 :11-12-2 . : . 1 . l9! . 1 1 .2445.

5 10 15 2 e 20 25 30
Figure 4. 16: X-Ray Diffraction Profile of CngOSS/PSZM Blends

97

Table 4. 2: Comparison of Peak Positions of CngOSS and CngOSS/PSZM
Blends (from X-ray Diffraction Curves in Figure 4.16)

 

Sample PEAK POSITION (° 20)
CngOSS 8.2 (10.77, 0.32) 11 (8.04) 19.1 (4.64, 0.37) 24.6 (3.61)

CngOSS/PS (50/50) 7.5 (11.78, 0.8) 10.5 (8.42) 18.8 (4.72, 0.88)
CngOSS/PS (20/80) 6.6 (13.55, 1.35) 18.5 (4.79, 0.78)

 

 

 

 

 

 

 

 

 

 

Note: In Tables 4.2 to 4.9, the first number in the parentheses is the d Spacing of the
peak (unit A). The second number in the parentheses is the 20 width of the peak (°).

and these two peaks shift to the left and broaden after CngOSS is
blended with PS. The peak positions are 82°20 and 19.1 °20 for the
unmixed CngOSS macromer, and 7.5 °20 and 18.8 °20 for
CngOSS/PSZM (50%) blend. The peak shifting of CngOSS macromer to
the left after it is blended with PS indicates that the
corresponding inter-planary d spacing of the CngOSS crystal increases
(Table 4.2): from 10.77 A to 11.78 A for peak 82°29, and from 4.64 to
4.7213. for peak 19.1 °20. Furthermore, the 20 width of these two peaks
increases from 0.325° to 08° for peak 82°20, and from 0375" to 0.88 °
for peak 19.1 °20, implying that the sizes of the crystal become small and
there are more defects in the crystals. The comparison between the 20
wt% and 50 wt% POSS loading blends of CngOSS/PSZM shows that with
a decrease of POSS loading, the diffraction peaks of CngOSS macromer
shift further to the left and broaden more (Table 4.2). The above results
reveal that the addition of PS interrupts the crystallization of CngOSS

macromer, and modifies the crystalline structures of the CngOSS

98

macromer. The degree of crystallinity of the CngOSS macromer in the
POSS/PS blends decreases with increasing of PS content.

The X-ray Diffraction curves of CngOSS and CngOSS/PSZM (20
and 50wt% POSS loading) are presented in Figure 4.17. Table 4.3 lists the

d-spacing and the 20 width of the diffraction peaks in Figure 4.17.

 

 

 

 

 

 

4.0E+05
3.5E+05 - 7.8 —°—Cy8POSS
; ~ —Cy8POSS/PS(20/80)
3.013+05 ~E ‘ ,. ~~-Cy8POSS/PS(50/50)
2.5E+05 f "
3‘ :
'65 L
520134-05 -;
_‘é :
1. E105 «i
5 : 8.2 18.5
: 11.8 23.4
1.0E 05 ~~
+ ; 10.1 l 15.5 18.2
50E+O4 it. i -‘ 1: r -. 3'4, 1,, I 7 I. ‘61.“! _
i. Win» 1 .‘ ”rm“ -. .... _,",
0.0E+00.~H:L~ (14411-4L1,."'T“1W1
5 10 15 20 20 25 30

Figure 4.17: X-Ray Diffraction Profile of CngOSS/PSZM Blends

Table 4. 3: Comparison of Peak Positions of CngOSS and CngOSS/PSZM Blends
(from X-ray Diffraction Curves in Figure 4.17)

PEAK
Sample POSITION (° 20)

CngOSS 7.8 (11.32, 0.22)] 15.5 (5.71) 18.2 (4.87) 23.4 (3.80)
CngOSSIPS(50/50)8.2 (10.77,0.44)l 11.8 (7.49) 18.5 (4.79)

 

 

 

 

 

 

 

 

 

CngOSSIPS (20/80) 10.1 (8.75)

 

99

 

We can see from Figure 4.17 that there are two well-defined peaks
in the x-ray curve of CngOSS/PSZM (50wt%) blend. These peaks
correspond to the two peaks in the neat CngOSS macromers, but with the
peak positions shifting to the right. This indicates that CngOSS
macromer form more close packing crystals (i.e. smaller d-spacing as
shown in Table 4.3) when it blended with PS. However, there is only one
small peak (10.1°20) in the x-ray curve of CngOSS/PSZM (20wt%),
implying that CngOSS macromer can be more well-dispersed in PS

matrix with a low POSS loading.

 

1 .20E+05

rj I I

   
 

5-9 —--Styreny18POSS

 

1005*“ “E —-Styreny18POSS/PS(20/80)
-- ; ~- Styreny18POSS/PS(50/50)
8.00E+O4
2;.
§6.00E+04
E
4.00E+O4 .

82%)"? ..
. I _ .. 1 wmflii‘L~)'

8.3 w
2.00E+04 a. ‘2‘: '1 ,» ..

OWE m 1 1 1 1 1 4 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 L 1 1

 

 

20

Figure 4.18: X-Ray Diffraction Profile of StyrenylgPOSS/PSZM Blends

As shown in Figure 4.18, there is only one small sharp peak in all

the X-ray diffraction curves of StyrenylgPOSS and StyrenylgPOSS/PSZM

100

Table 4.4: Comparison of Peak Positions of StyrenylgPOSS and
StyrenylsPOSSlPSZM Blends (from X-ray Diffraction Curves in Figure 4.18)

 

 

 

 

Sample PEAK POSITION (° 20)
StyrenylgPOSS 8.3 (10.68, 0.24)
StyrenylgPOSSlPS (50/50) 6.8 (12.99, 0.4)
StyrenylgPOSSlPS (20l80) 5.9 (14.97, 0.5)

 

 

 

 

(20 and 50wt% POSS loading). The 20 position of this peak is 8.3 for
StyrenylgPOSS, 6.8 for StyrenylgPOSS/PSZM (50wt%) and 4.9 for
StyrenylgPOSS/PS2M (20wt%). It can be seen that with the addition of
PS, the diffraction peak of the StyrenylgPOSS shifts to the left and the 20
width of the peak broadens (Table 4.4). The 20wt% POSS loading blend
has larger d-spacing and wider 20 width than the 50 wt% POSS loading
blend, indicating that in the low loading POSS blend, the crystalline

structures of POSS macromer are more impaired.

 

 

 

 

1.21~:+05 _
E -3 —°—Ph8Poss
1.0E+05 -- —Ph8P038/PS(20/80)
E ‘ Ph8POSS/PS(50/50)
8.0E+04
z:
§6DE+04 1
5 t 10.4l
4.0E+O4 f 318111444. . .
+ ~; ,5; ;. . . . '2 {Pffififihfibwfifirz‘ in?" _
: . .8 3 Z i. If}???$1’.=1‘§.-_._‘;:-_3_§:s,_ 1 1 0
2.0E+04 Jh 8 ‘ K8 . I f -’ tfih‘t“,4'a fin
i 18.3 . 2 . ., '
0.0E+00 J ‘ ‘ ‘ i 1 ‘ ‘ 1 ,L 1. 11291122 1 ?2

5 10 15 29 20 25 30

Figure 4. 19: X-Ray Diffraction Profile of PthOSSIPSZM Blends

101

Table 4.5: Comparison of Peak Positions of PthOSS and PhsPOSSIPSZM
Blends (from X-ray Diffraction Curves in Figure 4.19)

 

 

 

 

 

 

Sample PEAK POSITION (° 20) 1
8.1(10.92) 8.8(10.02) 18.3 (4.85)]

PthOSS 20.1 (4.42) 22.2 (4.0) 26.2 (3.40)]
PthOSS/PS (50/50) 10.4 (8.5) |
PthOSS/PS (20/80) 6.3 (14.0) |

 

 

 

 

The X-ray diffraction curves of the Pth088 and PthOSS/PSZM
(20 and 50wt% POSS loading) are shown in Figure 4.19 and their
corresponding d-spacing and the 20 width of the diffraction peaks are
listed in Table 4.5. There are many small peaks in the unmixed PthOSS
macromer (81°20, 88°20, l3.2°20, 16.5°20, 18.3°20, 20.l°20, 22.2°20,
22.9°20, and 26.2°20). However, only a very broad peak is observed in
PthOSS IPSZM (20 and 50wt%) blends, indicating that the PthOSS
macromers are well-dispersed in the PS matrix.

The X-ray diffraction profiles of the V3POSS macromer and
VgPOSS/PSZM blends (20 and 50wt% POSS loading) are displayed in Figure
4.20 and their corresponding d-spacing and the 20 width of the
diffraction peaks are tabulated in Table 4.6. The 20 and 50wt% POSS
loading blends still retain the 9.8°20 diffraction peaks with a little shifting.
In the 50wt% POSS loading blend, this diffraction peak shifts to the right,
and its corresponding d-spacing decreases (Table 4.20), while, in the 20wt%

POSS loading blend, this diffraction peaks shifts to the left, and its

102

corresponding d-spacing increases. The above results manifest that with the

decreasing of V3POSS loading, V3POSS and PS become more compatible.

 

8.0E+04

7.0E+04

6.0E+04 4

YTfTrWT

5.013+04 ~E

1ty

YYTWYT

4.0E+04 ‘

Intens

3.013+04 .. ...?"

2.013404 3

1.0E+04 .

 

0.01~:+00 ’
7

 
 
  
  
 
 
 
 
  

__vspossmsawsm
. .- V8POSS/PS(50/50)

 
 

 

 
 
  

' 20621.9”
.' . 19.7, "

i
.‘W‘nt .. ""-
11”"t8)..‘tgg;g;jz...z=;¥ *-

I"

.928. .1321 . 1 - 2.1122912317.

1 l
17

12 22 27

17 29

Figure 4. 20: X-Ray Diffraction Profile of VgPOSS/PSZM Blends

Table 4.6: Comparison of Peak Positions of VgPOSS and VgPOSS/PSZM Blends

(from X-ray Diffraction Curves in Figure 4.20)

 

 

 

 

 

 

 

 

 

 

 

Sample PEAK POSITION (° 29)
9.8 13.1 19.7 21.1 22.9 23.7
V8POSS (9.0, 0.48) (6.74) (4.50) (4.22) (3.88) (3.75)
10.8 13.9 20.6 21.9 23.9 24.6
V8POSS/PS (50’5")I (8.19, 0.7) (6.37) (4.31) (4.06) (3.72) (3.62)
9.4 22.5 23.3
V8POSS/PS (20ml (9.4.0.20) (3.95) (3.81)

 

 

Figure 4.21 shows the X-ray diffraction curves of STle7POSS and

its blends with PS2M (20 and 50wt% POSS loading). There are two well-

defined peaks in all the three specimens. The peak positions are 8.2°20

and 19.2°20 for the neat STle7POSS macromer, 7.8 °20 and 18.8 020 for

103

STICp7POSS IPSZM (50wt%), and 7.5 °20 and 18.9 °20 for STle7POSS
IPSZM (20wt%). As shown in Table 4.7, the corresponding interplanary d
spacing of the STle7POSS diffraction peaks increases after it is blended
with PS: from 10.72 A to 11.33 A (for 50wt% loading blend), and to 11.78
A (for 20wt% loading blend) for the peak 8.2°20, and from 4.61 A to 4.72
A (for the 50wt% blend) and, to 4.69A (for the 20wt% blend) for peak
19.2°20. The 20 width of the first peak expands from O.375° to 0.59° (for
the 50wt% blend), and to 1.5° (for the 20wt% blend). This expansion
reveals that PS modifies the morphology of the STle-lPOSS when they

are blended together.

 

 

 

 

 

1.2E+05
7 5 -—°—ST1Cp7POSS
1013 +05 -: ° —-—ST1Cp7POSS/PS(20/80)
' . - -~-ST1Cp7POSS/PS(50/50)
8.0E+04 '
a : 7.8i
§6013+04 i 18.9
E L ..
I-It L _ ‘ 1 _, L'.’
4.013+04 ~~ ’ 10.3 “)3? a),
3".“ . ““H’L” if; '3 1': ii . "hf “.51 . .
:Li *7 . '2 )18 8 1" W???" 31,2543: 3613):, 52a
2.0E+04 4; .
11 19.2 ' .
0.0E+00.1~ee1xteawn-aleeeae‘”.
5 10 15 20 25 30
20

Figure 4.21: X-Ray Diffraction Profile of STle-yPOSS/PSZM Blends

104

Table 4.7 : Comparison of Peak Positions of ST1Cp7POSS and STle-IPOSS IPSZM
Blends (from X-ray Diffraction Curves in Figure 4.21)

 

 

 

 

 

 

Sample PEAK POSITION (° 20)
STle-IPOSS 8.2 (10.72, 0.375) 11 (8.04) 19.2 (4.61)
STICp7POSS/PS(50/50) 7.8(11.33, 0.59) 10.8 (8.19) 18.8(4.72)
STlcp7POSS (20/80) 7.5 (11.78, 1.50) 18.9 (4.69)

 

 

 

 

The X-ray diffraction profile of V1Cp7POSS and Vle7POSS/P82M
(20 and 50wt% POSS loading), as shown in Figure 4.22 and Table 4.8)
manifests that after blending with PS, the V1Cp7POSS macromer in the
blend maintains similar peak features to the neat Vle7POSS macromer.

These three curves all have diffraction peaks with similar peak positions.

 

 
 
 
  
  

—— V1Cp7POSS
— V1Cp7POSS/PS(20/80)
~- Vle7POSS/PS(50/50)

18.7

 

 

 

 

2 0
Figure 4.22: X-Ray Diffraction Profile of V1Cp7POSS/PSZM Blends

105

Table 4.8: Comparison of Peak Positions of Vle-IPOSS and Vle-IPOSS IPSZM
Blends (from X-ray Diffraction Curves in Figure 4.22)

 

Sam!"e PEAK POSITION (° 20)

 

V1Cp7POSS 7.5 (11.7, 0.34) 10.3 (8.58) 18.5 (4.78)

 

V1Cp7POSS IPS (50/50) 7.7 (11.47, 0.5) 10.4 (8.50) 18.7 (4.74)

 

Vle-IPOSS IPS (20/80) 7.8 (11.33, 0.21) 18.9 (4.69)

 

 

 

 

 

 

The X-ray diffraction curves Of CyHele7POSS and CyHele7POSS
/PS2M (20 and 50wt% POSS loading) are shown in Figure 4.23, and their
corresponding d-spacing and the 20 width Of the diffraction peaks are
listed in Table 4.9. Figure 4.23 reveals that after blending with PS, the
diffraction peaks Of CyHe1Cp7POSS macromers maintain similar features

to the unmixed CyHele7POSS macromers.

 

 

 

 

 

1.8E+05 _
1.6E+05 ——~—CyHe1Cp7POSS

: -—CyHele7POSS/PS(20/80)
1.4E+05 ag - ‘-~*LCyHe1Cp7POSS/PS(SO/50)
1.2E+05 é

a; 1.0E+05 '7

s: t

93 :

E 8.0E+04 _E 18.4
6.0E 04 i A. 19.6
4.0E+O4 4),, a" have" - .

”51¢ ”Ml I {PL ......
2.0E+04 - . 7 86 19,3 1 4M.”
0.0E+00n‘1"i“‘4+"“:““i“*‘1

5 10 15 20 25 30

2 0
Figure 4.23: X-Ray Diffraction Profile of CyHele-yPOSS/PSZM Blends

106

Table 4.9: Comparison of Peak Positions of CyHele7POSS and
CyHele7POSS IPSZM Blends (from X-ray Diffraction Curves in Figure 4.23)

 

 

 

 

samp'e PEAK POSITION (0 20)
CyHeleyPOSS 7.7 (11.47) 8.6 (10.27) 18.6 (4.77) 19.3 (4.60)
CyHe1Cp7POSS IPS
(50,50) 8.6 (10.27, 0.84) 19.6 (4.53)
CyHele7POSS IPS
(20/80) 7.7 (11.47, 1.8) 18.4 (4.82)

 

 

 

 

 

 

 

The above results suggest that the addition Of PS modifies the
crystalline structures Of the POSS macromers, and the degree Of
modification depends on the compatibility level between the two
components. The higher the compatibility between POSS and PS, the less
the crystallinity Of the POSS macromers. When POSS and PS are miscible,
POSS disperses homogeneously in the PS matrix, such as in the case Of
PthOSS/PS blends, where P-thOSS is amorphous in the PS matrix. When
POSS macromers and PS are partially compatible, the d-spacing and
widths of the diffraction peaks Of the P088 macromers increase after they
are blended with PS.

POSS loading also has effects on the crystalline structures Of the
POSS macromers in the POSS/PS blends. Because POSS macromers in the
20wt% POSS loading blends have better compatibility with PS than those
in the 50wt% POSS loading blends, the POSS macromers in the low

loading blends are less ordered.

107

4.4.2 Effects of PS Molecular Weight:

Figures 4.24 and 4.25 present the effects of the PS molecular weight
on the microstructures of the POSS/PS blends (20wt% POSS loading).
Compared to the diffraction peaks of the high molecular weight
PS2M/CngOSS and PSZM/ST1Cp7POSS blends, the diffraction peaks of
the low molecular weight PS216K/CngOSS and PSZl6K/ST1Cp7POSS
blends are more distinctive, implying that POSS macromers are more
ordered in the low molecular weight PS matrix than in the high molecular
weight PS matrix. As we explained earlier, this is because POSS macromers
are easier to phase separate from the low molecular weight (low viscosity)

matrix than from the high molecular weight matrix (high viscosity).

 

3.513405 _

f ——Cp8Poss
3.0E+05 —; ——Cp8POSS/PS2M(20/80) 19.0
; ----- Cp8POSS/PS216K(20/80) f

2.5E+05 f ‘x_

2.0E+05 —§

Ity

1,513+05 J

Intens

1.0E+05 f

5.0E+O4 { .

 

 

 

 

0.0E+00 2’
5 10 15 20 20 25 30

Figure 4.24: X-ray Diffraction Profiles of CpsPOSS/PS Blends
(20wt% POSS Loading) with Different Molecular Weight PS

108

 

 

 

 

4.0E+05 .
_ —~——ST1Cp7POSS
3,551.05 -5 — ST1Cp7POSS/PS2M(20/80)
: ------ ST1Cp7POSS/PS216K (20/80)
3.015+05 aE
: 19.0
2.5E+05 4 fr.
>~. E r' 5?.
g 2.0E+05 —; .3 '8.
E E ,9! 8.
1.5E+05 -: 7 5 7.8 .1; ‘31
Z "N‘ ”I“
1.013 05 -i L . .... 4.48"
+ ‘ _. . 0* ‘5’ {18.9
5.013+04 M“, 8.2
L 19.2 _
0.0E+00.~+L:HH:~~;L-11,444.,
5 10 15 20 20 25 30

Figure 4.25: X-ray Diffraction Profiles of ST1Cp7POSSI PS Blends
(20wt% POSS Loading) with Different Molecular Weight PS

4.4.3 Summary:

1.

The crystallography of POSS macromers in the POSS/PS blends
depends on the compatibility between the two components. The

more compatible POSS and PS are, the less crystalline the POSS

macromer becomes when it blend with PS. When the two
components are miscible, the POSS macromer disperses
homogeneously in the PS matrix. Among the eight POSS

macromers studied, PthOSS is the most compatible one with

P8. All the other POSS macromers: ST1Cp7POSS,

StyrenylgPOSS, CngOSS, CngOSS, VgPOSS, Vle7POSS, and

CyHele7POSS are partially compatible with PS.

109

2. With decreasing Of POSS loading, POSS macromers are more
well-dispersed in the PS matrix.
3. POSS macromers are more ordered in the low molecular weight

polymer matrix than in the high molecular weight one.

4. 5 Glass Transition Behaviors of POSS/PS Blends

This section examines the glass transition characteristics Of a series
of POSS/PS blends. The intention is to see how the addition Of POSS
macromers modifies the microenvironment Of the polymer chains, and how
this modification affects the molecular motion Of the polymer chain
segments: retarding the chain motion, enhancing the chain motion or no
impact? The information reflects the compatibility and interaction
between POSS macromer and polymer.

The glass transition temperature (Tg), Obtained from DSC, is used

here to characterize the motion of the polymer chain segments.

4.5.1 Effects of POSS Chemistry and POSS Loading:

Figures 4.26 to 4.41 Show the influence Of different POSS macromers
on the Tg behaviors Of POSS/PSIM blends (PS: Mw=1600,000). Their
results are listed in Table 4.10. Comparing the Tg values Of POSS/PS
blends with that of the neat PS, we can see that the additionof POSS
macromers lowers the Tg value of PS and also broadens the transition

width, irrespective Of the types Of POSS macromers.

110

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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111

 

95>
N

.b
A

  
 

Heat Of Flow (J/g)
95 b
oo 05

Tg: 112.2°C

—PSIM

 

 

 

 

1 L 1 1 l 1 m 1 1 l 1 1 1 1 1 I 1 L
' e I I I

50 70 90 l 10
Tenperature (° C)

Figure 4.26: DSC Curve of PSlM

150

 

0.1 “E
0.2
”’0 0.3
o 0.4 i
“a 0.5
5:3 0.6 4
0.7
0.8

Fl w(J/

 

E _PSlM/CpSPOSS(20wt%)

 

 

 

0.9 ”
40 60 80 100 120 140

Temperature (0 C)

Figure 4.27: DSC Curve of PSlM/CngOSS (20wt% POSS Loading)

112

 

—PSlM/Cp8POSS(50wt%)

Heat Of Flow (J/g)

 

 

 

 

40 60 80 100 120 140 160 180
Temperature (0 C)

Figure 4.28: DSC Curve of PSIM/CpnPOSS (50wt% POSS Loading)

 

_PSIM/CpBPOSS(80wt%)

Tg: 108.9°c

 

Heat Of Flow (J/g)
,8:
N
111

 

 

50 70 90 1 10 130 150 170
Temperature (°C)

Figure 4.29: DSC Curve of PSlM/CngOSS (80wt% POSS Loading)

113

 

0.3 ,
0.35 —PSlM/Styreny18POSS(20wt%)

0.4
0.45

.b
M
III—YT

0.55

.b
0\

eat Of Flow (J/g)

H
b8
\ILII

 

0.75

 

 

 

60 80 100 120 140 160 180
Temperature (° C)

Figure 4.30: DSC Curve of PSIM/StyrenylgPOSS (20wt% POSS Loading)

 

0.3 _
: —PSlM/Styreny18POSS(50M%)

0.35 -3

0.4 i

0.45 «E

0.5 —;/——w8°c

Heat Of Flow (J/g)

 

 

 

Temperature (° C)
Figure 4.31: DSC Curve of PSlM/StyrenylgPOSS (50wt% POSS Loading)

114

-0.3
-0.35 -:

 

IT

-— PS 1M/StyrenylSPOSS(80wt%)

IIIITTTI

)
,b
Sis-i

Tg: 105.5°C

 

-0.55 7E

Heat Of Flow J/
b
O‘

-0.65 -
-0.7 ~
-0.75 4:

0.8
60 80 100 120 140 I60 180

Temperature (° C)

IIrrfifiW’TTIII I

 

 

 

Figure 4.32: DSC Curve of PSIMIStyrenylsPOSS (80wt% POSS Loading)

-0.1

 

— PS 1M/Ph8POSS(20wt%)

i
-0.2 3:

g5
DJ
1

    

g:
4;

Tg: 484°C

,5:
£11

Heat Of Flow (J/g)

9'3 S5
\l O
l l

 

 

 

b

00
r-
L.
l.
C
l.
C

d).
l.
I
L-

10 30 50 70 90 110 130 150 170
Temperature (°C)

Figure 4.33: DSC Curve of PSlMIPhsPOSS (20wt% POSS Loading)

115

 

{ — PS 1M/Ph8POSS(50wt%)

Heat Of Flow (1/ g)

 

 

 

 

-11
C
-1.2LALLLWLLLVLLLWLHILH11111111111114“
-10 10 30 50 70 90 110 130 150
TemperatureC’C)

Figure 4.34: DSC Curve of PSlM/PthOSS (50wt% POSS Loading)

0

 

— PS 1M/PhSPOSS(80wt%)

IIIIITIIIIIIIIIIIITI

Heat Of Flow (J/g)

.bbsbbbbb
«anaemic—e

 

 

 

 

Figure 4.35: DSC Curve of PSlM/PthOSS (80wt% POSS Loading)

116

 

E -—-PSlM/Isobu8POSS(20wt%)

Heat Of Flow (J/g)
.b .b .3:
8: ii a 8 a S

 

 

 

95
m

 

Terrperature (°C)
Figure 4.36: DSC Curve of PSlMIIsobugPOSS (20wt% POSS Loading)

 

— PS 1M/Isobu8POSS(50wt%)

Heat Of Flow (J/g)
6: .b .b
A m

,b

 

 

 

 

Figure 4.37 : DSC Curve of PSlM/IsobugPOSS (50wt% POSS Loading)

117

 

Heat of Flow (J/g)

 

 

— PS lM/Isobu8POSS(80wt%)

Tg: 110.7°C

  

 

 

 

llllllllllllllllllllllllllllllllll

 

100 120
Temperature (° C)

Figure 4.38: DSC Curve of PSlMIIsobugPOSS (80wt% POSS Loading)

.6
u

b
4;

Heat of Flow (J/g)

,6:
Ln

 

   

— PSlM/STle7POSS (20wt%)

Tg: 105.8°C

  

 

 

 

100 120
Temperature (°C)

Figure 4.39: DSC Curve of PSIMISTleyPOSS (20wt% POSS Loading)

118

Heat of Flow (J/g)

Heat of Flow (J/g)

 

IfT

— PSlM/STICp7POSS (50wt%)
0.2 «r

-O.3 ~L

Tg: 105. 1°C

55
A

   

 

-0.5 +
t

-O.6 —3

fifT I

 

 

 

4O 60 80 100 120 140 160 180
Temperature (°C)

Figure 4.40: DSC Curve of PSlM/ST1Cp7POSS (50wt% POSS Loading)

 

— PS lM/STle7POSS(80wt%)

T ITH TTWTT

 

 

 

 

40 60 80 100 120 140 160 180
Temperature (°C)

Figure 4.41: DSC Curve of PSlMlSTlegPOSS (80wt% POSS Loading)

119

Among all of the POSS/PS blends studied, PthOSS/PSIM blends
(Figures 4.33, 4.34, and 4.35) have the most dramatic drop in T8 at all
compositions. The reductions in TE; values are 56.9%, 66.8% and 107.2%,
for the 20, 50, and 80 wt% PthOSS loading blends respectively (Table
4.10), while the ST1Cp7POSS/PSIM blends (Figures 4.39, 4.40, 4.41 and
Table 4.10) have a very small decline in Tg at all compositions---only
about 2~6%.

Comparing the Tg values of all the 20wt% POSS loading blends
(Table 4.10), the Tg of ST1Cp7POSS IPSlM blend decreases only 5.7%,
much less than the Tg drops of CngOSS/PSIM (30.4%),
IsobugPOSS/PSIM (22.0%), PthOSS/PSIM (56.9%), and
StyrenylgPOSS/PSIM (20.3%).

As seen in Table 4.10, for all the 50wt% POSS loading blends, the
Tg values of blends ST1Cp7POSS/PSIM, Isobu8POSS/PSIM, and
StyrenylgPOSS/PSIM decrease only about 5%, while the Tg values of
CngOSS/PSIM, and PthOSS/PSIM fall significantly more, 20% and
66.8%, respectively. Among the 80wt% POSS loading blends, the Tg value
of all the blends is close to the Tg of unmixed PS, except for the
PthOSS/PSIM blend.

It can be seen from Table 4.10 that with the increasing of POSS
loading the Tg values of the POSS/PSlM blends are more close to the T8
of the neat PS, but with one exception: for PthOSS/PS blends, the Tg

values, decrease with increasing POSS loading.

120

In comparison with the glass transition zone width of the neat PS,
the transition widths broaden in all the POSS/PSIM blends. However, the
50wt% loading POSS blends have broader transition zones than the 20wt%

and 80wt% blends.

4.5.2 Discussion

The above results manifest that POSS macromers behave like
plasticizers in the PS matrix. The addition of POSS macromers into PS
decreases the T8 and broadens the transition zone of the PS.

How POSS macromers influence the polymer chain motions depends
mainly on the following two factors:

First is the interaction force between POSS macromers and polymer
chains. One extreme case is there are no any kind of interactions between
POSS and polymers. In this case, POSS macromers have no effect on the
mobility of the polymer chains. Another extreme case is when the POSS
macromers are attached to polymer chains. In this case, the mobility of
the polymer chains is retarded due to the massive POSS cage.

The second factor is the compatibility between the polymer and the
POSS macromers. Good compatibility results in thorough dispersion of
the POSS macromers in the polymer matrix, and fineness of the dispersion
sizes. The degree of dispersion of the POSS macromers is the fundamental
factor that decides if POSS macromers affect the mobility of the polymer

chains.

121

When POSS macromers have a high degree of compatibility but
weak interactions with PS, the blending of POSS macromers into PS
causes a dramatic drop in the Tg value of the PS. This is because that the
high degree of compatibility between the two components assures a
homogeneous dispersion of POSS macromers in the matrix (i.e. they don’t
aggregate), and the absence of favorable interactions between the POSS
macromers and the polymer chains renders POSS macromers acting like
plasticizers in the polymer matrix. As a result, the addition of POSS
macromers expands the distance between polymer chains, and increases
the free volumes of the polymer chains, leading to a temperature drop and
width broadening of the glass transition. The more the compatible the
two components are, the more the Tg drops (such as in the case of .
PhsPOSS/PS blends).

The addition of POSS macromers, with poor compatibility with PS,
into PS also decreases the Tg of the PS, but signifiCantly less than the
drop in T3 observed for POSS/PS blends with good compatibility. Since
POSS macromers with low compatibility aggregate in PS matrix, polymer
chains are not effectively affected by the POSS macromers owing to the

severe phase separation.

4.5.3 Summary:

The proceeding results indicate that there is no favorable

interaction between POSS macromers and polymeric chains. POSS

122

macromers behave like plasticizers in the PS matrix, which results in the
decrease of the glass transition temperature of the PS and the broadening
of the transition zone of the PS.

The more compatible between the POSS macromer and the polymer,
the more the Tg drops. Among the five POSS/PS blends studied
(CngOSS/PS, Styreny18POSS/PS, PthOSS/PS, IsobugPOSS/PS,

ST1Cp7POSS/PS), the PthOSS/PS blend has the lowest T8.

4.6 Thermal Stability Studies of POSS/PS Blends:
4.6.1 Effects of POSS Chemistry and POSS Loading:

Figures 4.42 to 4.49 are the TGA curves of POSS/PS2M blends {PS
Mw: 2316000, 20 and 50wt% POSS loading).

As shown in Figures 4.42 to 4.47, the Tdcc values of the 20 and 50wt%
loading blends of CngOSS/PSZM, CngOSS/PSZM, VsPOSS/PSZM,
ST1CP7POSS/P82M, V1Cp7POSS/P82M, and CyHeIprPOSS/PSZM are all
lower than the Tdcc values of their neat components. StyrenylgPOSS/PS2M
blends (20wt% and 50wt%) (Figure 4.48) have Tdec values higher than the
Tdcc of PS but lower than the Tdcc of StyrenylgPOSS. As shown in Figure
4.49, the 20wt% PthOSS/PSZM blend has a lower Tdec than the PS and
PthOSS, while the Tdcc of the 50wt% blend falls between the Tdec values of
PS and PthOSS. Comparing the Tdec values of the 50wt% blends with those
of the 20wt% blends, we can see that all the 50wt% POSS loading blends

have higher Tdec than their corresponding 20wt% POSS loading blends.

123

 

120

 

 

 

 

 

 

  

 

 

 

 

 

 

 

    
  

 

 

 

 

l: 2:
371.56°C 95.00% 381.23°C 95.00%
100
, ‘ Residue:
3. 4 \ \ 12 5.644%
80~ 209. 56°C 95. 00% 263 15°C 95 00 -\ (0-2824mg)
Q I Residue:
E . l 4. 2.672%
in 60‘ (0.3374mg)
0
3 Residue:
40- 3; 0.9099%
(0.1591mg)
Residue:
20+ CPSPOSS'“1 0.6641%
PSZM"'3 2: (0 01359mg)
— PSZM/Cp8POSS (20%)---3 '
__— PS2M/Cp8POSS (50%)---4 é—Ej
100 200 300 400 500 600 700
Temperature (°C)
Figure 4. 42: TGA Curves of PSZM/CngOSS Blends.
120
4 4: 380.15°C 95.00%
2: 381.23°C 95.00%
100 -=-;-::-— ~~~~~~ 1‘
N" —————— 397.50°C 95.00%
3: 208. 26°C 95. 00%
80- Residue:
A 1; 14.73%
2% (0.8543mg)
f3? 60‘ Residue:
g 1 3; 1.746%
(0.3840mgl)
40“ Residue:
1 4: 1.645%
20 Cy8POSS---1 (02375“)
1 ___. pszm---2 Residue:
. ___. PS2M/Cy8POSS(20%)---3 '\ 2. 0.6641%
0 —— PSZM/CySPOSS(5()%)---4 J ' (0.013591%
100 200 300 400 500 600 70

Temperature (°C)

Figure 4.43: TGA Curves of PSZM/CngOSS Blends.

124

 

 

 

 

 

 

 

 

 

 

 

 

    
 
 
 

 

 

 

 

 

 

120
4: 250.11°C 95.00%
1: 251.28°C 95.00%
100-
Residue:
’ 1; 47.87%
80+ (4.763mg)
’3 Residue:
E s \\ 4: 18.24%
E 607 I (4.707mg)
'3'30 ‘ I Residue:
3 I - I 3: 9.484%
404 I I I (1.725mg)
I = I Residue:
. ' . 0.66417
vsposs---1 I - K. 2- 00135;“
ZOI 1232“---) I ‘T “ __ 7‘ ( ' g)
. —— Ps2MN8POSS(20%)---3 \ ......... _,
0 —— PS2M/V8POSS(50%)---4 .
100 200 300 400 500 600 700
Temperature (°C)
Figure 4.44: TGA Curves of PSZM/VgPOSS Blends.
120
4: 1: R 'd
‘ o 381.22°C 95.00% 681 us:
100 .. 357.62 C 95.00% 2: 1: 39.80%
;;:C;:z::::_. 381.23°C 95.00% (2-89lmg)
218.79°C 95.00% 3180.641” 018 RCSIdue:
801 4; 18.77%
”'9‘ °\ . (3.233mg)
& .
:7 I . Residue:
'50 60‘ - . 3: 7.189%
E I\ \ (1.580mg)
- \ Residue:
I. ‘\, 21 0.151541%
—— PSZM--—2 \.
. —— PSZM/STle7POSS (20% --3 \-\.\___.+
0 —- PSZM/STlCp7POSS(50%)- 4 J
100 200 300 400 500 600 700

Temperature (°C)

Figure 4. 45 : TGA Curves of PSZM/STle-IPOSS Blends.

125

120

 

 

 

 

   
   

 

 

 

 

 

 

 

 

 

      
    
 
  
 
 

 

 

 

4; 316.64°C 95.00%
100 l: 369.05°C 95.00%
fi'\‘§ t-Fz. 2.2;: K 2: 381 23°C 95 00% Residue:
3: 244. 76°C 95. 00% 1: 20.50%
80« (2.488mg)
§ Residue:
:9 4; 5.148%
.50 60. (0.7933mg)
'63 Residue:
B 3; 2.620%
40 (0.5077mg)
Residue:
; . 0.6641%
20- ___ 1‘)’ 91317393541 I.\ 2' (0.01359mg:
. ————- PSZM/Vle7POSS(20%)- -3\\ QQ
0 ___— - PszM/v le7POSS(50‘72 )--4 \';.-—-—':‘:i
100 200 300 400 500 600 700
Temperature (°C)
Figure 4.46: TGA Curves of PSZM/V1Cp7POSS Blends.
120
I 1; 348.14°C 95.00%
100 —-~—.~; Q Q
“ ==““-++~. 2: 381.23°C 95.00%
3302.79°C 95 00% -\ R _d
o , . CS] L162
8; I \ I (0.2682mg)
:1 I I Residue:
g, 60- . . 4; 2.444%
0 I II (0.2565mg)
3 v .
40 II Resrdue:
‘ I 3: 1.453%
I (0.2006mg)
C HelC 7POSS---1 Residue:
20— pgzMu-g I 2;0.664l%
—- PSZM/CyHele7POSS(20%) - (0.01359mg)
0 —— PSZM/CvHele7POSS(50%)— «I
50 150 250 350 450 550 650
Temperature (°C)
Figure 4. 47 : TGA Curves of PSZMICyHelCmPOSS Blends.

126

120

 

 

 

 

 

 

  

 

 

 

 

 

 

 

    
 
  

 

 

4:
3: 410.86°C 95.00% 424.92%: 95_()0%
100 m '“= ————————— w. 1: 458.18°C 95.00%
2: 381.23°C 95.00% . .
. I .Re51due:
80_ I . 1- 79.12%
A I I (9.466mg)
§ - I Residue:
E 60- I I 4:30.55%
.2339 I I (4.288mg)
3 I '\ Residue:
40- I \~\_ 3; 14.65%
I \-\ (2.934mg)
20- _-_ ggfii‘fipossml \QQQQ 1 Residue:
—— PSZM/Styrenyl8POSS (20 )---3 2: 0068:3123
0 -——— PSZM/StyrenylSPOSS(50%)-«4 . ( : mg)
100 200 300 500 600 700
Temperature (°C)
Figure 4.48: TGA Curves of PSZM/StyrenylgPOSS Blends.
120
2: 4:
381.23°C 95.00% 431.67°C 95.00%
100 '\.\ ““““““““““ 1:0
3: ~\+.Q ________ 487.97 c 95.00%
‘ 204.42%; 95.00% 385.53%? 02.54% Residue:
807 - ' 1; 52.71%
A I . (98ng)
O
i? I - Residue:
.5060- I . 4; 26.13%
g I I I (6.427mg)
. Q.
_ I \x. Residue:
40
I \ 3; 8.891%
I '\.QI (1.537mg)
Ph8POSS---l ‘
20 ———— PS2M ------ 2 \‘\.\_ Residue:
. —— PSZM/Ph8POSS(20%)--3 \-~-—-—+ 2, 0.6641%
0 ___ PSZM/Pl18POSS(50%)--4 j 1 . l' (0.0'1359m )
100 200 300 400 500 600 700

Temperature (°C)

Figure 4.49: TGA Curves of PSZM/PthOSS Blends.

127

The addition of POSS macromers into PS renders the POSS/PS
blend higher residues than the neat PS. As seen in Figures 4.42 to 4.49,
the residues of all the POSS/PS blends fall between the residues of the
unmixed POSS and PS. The 50wt% POSS loading blends have higher
residues than their corresponding 20wt% POSS loading blends.

Comparing the TGA curves of all the POSS/PS blends with those of
their neat components, we can see that the decomposition paths of the
blends are different from those of their unmixed components and vary
with the types of POSS macromers.

At the early decomposition stage (before 380°C), all the POSS/PS
blends start losing weight at lower temperatures than both the POSS
macromers and PS, even though the 50wt% blends exhibit better thermal
stabilities than the 20wt% blends.

However, in the middle stage of the decomposition, the
decomposition paths of the POSS/PS blends exhibit two cases. Firstly, for
blends in which the Tdec of POSS macromer is higher than the Tdec of PS,
their decomposition curves fall between the curves of the unmixed
components, such as CngOSS/PS (Figure 4.43), ST1CP7POSS/PS (Figure
4.45), Styreny18POSS IPS (Figure 4.48), and PthOSS/PS (Figure 4.49)
blends, and the 50wt% blends have better thermal stabilities than their
corresponding 20wt% blends. Secondly, for blends in which the Tdec of
P088 macromer is lower than the Tdcc of PS, their decomposition paths

are somewhat complicated: during one temperature range, the thermal

128

stabilities of the blends fall between those of the unmixed components,
while at another temperature range, the thermal stabilities of the blends
are better than both the neat components, such as the CngOSS/PS (Figure
4.42), CyHele-IPOSS/PS (Figure 4.47), VIprPOSS/PS (Figure 4.46),
V3POSS/PS (Figure 4.44) blends. However, in the second case, the 20wt%
blends exhibit higher thermal stabilities than their corresponding 50wt%
blends.

At the final stage of decomposition, the TGA curves of all the
POSS/PS blends fall between the TGA curves of the pure POSS
macromers and PS. The 50wt% POSS loading blends have higher stability

than their corresponding 20wt% POSS loading blends.

4.6.2 Summary:

POSS/PS blends exhibit improved thermal stability when using
POSS macromers with higher decomposition temperatures and residue
yields than PS. StyrenylgPOSS/PS and PthOSS/PS blends exhibit better

thermal stabilities than other POSS/PS blends.

129

CHAPTER 5

MORPHOLOGY AND PROPERTIES OF
POSS/POLYDIMETHYL SILOXANE (PDMS) BLENDS

 

 

5.1 Introduction:

The morphology and performance of the POSS/PDMS blends were
next examined. Our research studies mainly focused on their rheological
properties.

The compositions of polysiloxanes include both inorganic and
organic portions. The polymer backbone is composed of alternate silicon
and oxygen atoms. Each silicon atom has two organic groups attached to
it. The chain-end silicon atoms have a third group (organic, hydroxyl, or
alkoxy group) to satisfy silicon’s fourth valence.

Polydimethyl siloxane (PDMS), which was used in this study,

consists of methyl group substitution and can be represented as in Figure 5.1.

CH3 CH3 CH3
R—Si—f—O —S|i —]n—O—-fi—R
CH3 CH3 CH3

Where R can be an organic, hydroxyl, or alkoxy group.

Figure 5.1: Chemical Structure of Polydimethyl Siloxane (PDMS)

There are two reasons why we have chosen PDMS as one of the

polymer models for the studying of POSS/polymer blends. First, because

130

of their similarity in chemical compositions, POSS macromers have better
compatibility with PDMS than with other polymers, and good
compatibility is a crucial requirement for fabricating multi-component
systems with specific properties. Second, POSS macromer has the
potential to be a reinforcing filler for PDMS. The tensile strength of a
cross-linked non-reinforced high molecular weight PDMS is in the range
of about 0.34 MPaI68]. This value is too low to satisfy the property
requirements of most applications, hence, the reinforcement of PDMS is
necessary. We expect that because of their organic/inorganic feature and
the nanometer-size of the POSS macromers, POSS macromers would have
significant potential as a nano-reinforcing filler for PDMS.

In the following studies, X-ray diffraction was utilized to
characterize the morphologies of the POSS/PDMS blends. Thermal
stability of the POSS/PDMS blends was studied by TGA, and the
rheological measurements of POSS/PDMS blends were carried out with a

Universal Dynamic Spectrometer.

5.2 Experimental:
5.2.1 Materials:
5.2.1.1 Polydimethyl siloxanes (PDMS):
A number of different molecular weight PDMS were provided by
the Silicone Division at General Electric Company. Their characteristics

are presented in Table 5.1.

131

Table 5.1: Characteristics of Polydimethyl Silioxane (PDMS)

 

 

 

 

 

Avera e . .
2:33: M01433; ...;::::::82;oc
Weight
SE72 polydimethylsiloxane gum 525,000 ~
VisclOOM polydimethylsiloxane fluids 139,000 100000
Visc60M polydimethylsiloxane fluids 116,500 60000
Visc3OM polydimethylsiloxane fluids 91,700 30000

 

 

 

 

 

 

Note: (1) Provided by GE Silicone.

5.2.1.2 POSS Macromers:

POSS macromers used for the experiments described in this chapter
include CngOSS, IsobugPOSS, VgPOSS, ST1Cp7POSS, StyrenyIICp-IPOSS,
CyHele-IPOSS, Vle-IPOSS, STlIsobu7POSS, and Styrenylllsobu7POSS.

See Table 3.1 and Figure 3.1 for their chemical structures.

5.2.2 Sample Preparation:
5.2.2.1 Samples Preparations for Thermogravimetric Analysis (TGA) and X-
Ray Diffraction:

Preparations of POSS/PDMS blends were performed by dissolving
PDMS and POSS macromer in toluene for 12 hours; evaporating the solvent,
and then by drying the samples under vacuum for more than 12 hours at 60°C.
5.2.2.2 Samples Preparations for Rheology tests:

POSS and PDMS were dissolved in toluene for 12 hours. The solution
was then poured into methanol, causing the POSS/PDMS blend to

precipitate. This precipitate then was vacuum-dried for 24 hours at 60°C.

132

5.2.3 Characterization Techniques:
5.2.3.1. Morphology Characterization:

The morphologies of POSS/PDMS blends were characterized by X-ray
diffraction techniques. X-ray diffraction measurements were performed using a
Scintag XRD 2000 with a Cu target; 20 angle ranged from 5° to 30°; Step size
and scan rate used here was 0.03° and 2° /min, respectively.

The x-ray diffraction pattern obtained from a diffractometer records
the X-ray intensity as a function of diffraction angle. The inter-atomic
spacing is determined by Bragg’s law: d = n}. / (2sin0)

Where (1 is the inter-atomic spacing; A is the wavelength of the x-ray
(1:1.5406A for Cu target); 0 is the diffraction angle.
5.2.3.2 Thermal Stability Characterization:

Thermogravimetric analysis was carried out on a Hi-Res TGA 2950
under Nitrogen atmosphere. Temperature range used was 25 to 600°C;
Heating rate utilized was 20°C/min. Tdcc is taken as the temperature where
5% weight loss occurred. Residue is the weight percent of the sample
remains after the TGA test.
5.2.3.3 Rheology Test:

The rheological properties of POSS/PDMS blends were determined
using a stress-controlled rheometer, Paar-Physica UDS-200, equipped
with a force-air oven with temperature ranged from —150°C to 600°C. A

25mm diameter cone-and-plate with an angle of 2° was used in this study.

133

The existence and extent of the linear viscoelastic (LVE) regime was
determined by measuring the dynamic storage modulus, (G’), as a function
of shear stress (test range is 24~2480Pa) at a constant frequency of 5H2. The
results showed that the POSS/PDMS blends exhibit linear viscoelasticity in
the experimental conditions tested.

Measurements were performed in a temperature range from 30°C to
200°C. The experimental protocol used was as follows. The sample was
loaded at 30°C and then the temperature was step-wise gradually increased
until the desired annealing temperature was reached. Frequency sweep
experiments were performed at each chosen temperature. Prior to each
measurement, the temperature was held for 15 minutes to allow for
equilibration. Upon reaching the desired annealing temperature, frequency
sweep experiments were performed as a function of annealing time.

Creep tests were conducted for the un-gelled (i.e. before annealing)
and gelled (i.e. after annealing) POSS/PDMS blends at 30°C.

The following types of measurements were utilized in this research:

-—-Frequency Sweep: 0.315—315 rad/s at a Shear Stress 245 Pa;

---Shear Stress Sweep: 24-2480 Pa at a frequency 5Hz (31.4 rad/s);

---Strain (©) Sweep: l-200% at a frequency 10Hz (62.9 rad/s);

---Steady State: Shear Rate: 0.01-1005'1;

---Creep test: A constant shear stress is imposed on the sample, and

time-dependent rheological information is recorded.

134

5.3 Morphological Structures of POSS/PDMS Blends

Because the glass transition of PDMS (Tg:-120°C) is well below
ambient temperature, the specimens of POSS/PDMS blends are very soft.
The TEM sample preparations of the POSS/PDMS blends require a special
technique, which included sample micro-toming with a diamond knife at
near liquid nitrogen temperatures (-150°C). Due to this complexity of the
TEM sample preparations, in this section, we only employed X-ray
diffraction technique to characterize the morphological structures of the
POSS/PDMS blends.

The x-ray diffraction curves of CngOSS/SE72, VgPOSS/SE72,
Isobu3POSS/SE72, ST1Cp7POSS/SE72, Styrenylle7POSS/SE72,
CyHeICp7POSS/SE72, V1Cp7POSS/SE72, STlIsobU7POSS/SE72,‘ and
Styrenylllsobu7POSS/SE72 blends (20wt% POSS loading) are shown in
Figures 5.2 to 5.10. These figures show that compared to the x-ray diffraction
curves of their neat POSS macromers, the microstructures of the POSS
macromers are all modified to a various degree after they are mixed with
PDMS.

As shown in Figure 5.2 and 5.3, after CngOSS, and VgPOSS
macromers are blended with PDMS, they still retain similar diffraction
features to their corresponding neat POSS macromers, indicating that
these two POSS macromers form their own phases, and their

microstructures are not greatly affected by PDMS.

135

 

1.6E+05 ’

'Cp8POSS

1.4E+05
"— SE72/Cp8POSS(20%)

l .2E+05

l .0E+05

lty

8.0E-I04

Intens

6.0E+04

4.0E+04

2.0E+04 »

 

 

 

 

00132.00“
5 10 15 20 25 30

2 0
Figure 5.2: X-ray Profile of SE72!CngOSS Blend (20 wt% POSS loading)

 

9.5E+04 : I
8.5 -5 " "*H-vsposs
5' °' E ——SE72N8POSS(20%)
7.5E+04 ~g
6.5E+04
€559.04 -E
c _

245154.04
3.5E+04
2.5E+04
1.5E+04 va ,‘

 

 

 

 

5.0E+03 ‘
5 10 15 20 25 30

Figure 5.3: X-ray Profile of SE72/V3POSS Blend (20 wt% POSS loading)

136

 

. ”---..." Isobu8POSS
2.5E+06 «Z _ SE72/Isobu8POSS(20%)

 

 

 

 

2 0
Figure 5.4 X-ray Profile of SE72/IsobusPOSS Blend (20 wt% POSS loading)

 

77000 7;
I anm’oss

67000 —: — SE72/ST1Q)7POSS(20%)

57000 -E

47(11) ‘2

Intensity

37000 f
27000 IE

17000~- a

 

 

 

_ . ”I ,. ,1 I.
l- I “ I ’
l I 1 l
7(XI) ‘ j

2 0
Figure 5.5: X-ray Profile of SE72/ST1Cp7POSS Blend (20 wt% POSS loading)

137

 

8.8E+04 " Styrenylle7POSS
_ SE72/Styrenyl 1Cp7POSS(20%)

 

 

5 10 15 20 25 30
2 0

Figure 5.6: X-ray Profile of SE72/Styrenyl1Cp7POSS Blend (20 wt% POSS loading)

 

7.7E+04 .
I '"" CyHele7POSS

6.7E+04 7; —— SE72/CyHeICp7POSS(20%)
sflMMI

Mmmn¥

tensit

ENEMI

 

 

 

 

2.7E+04 “E
7mws. . 4-Ieliegi“b*‘11*r’
5 10 15 20 25 30

20

Figure 5.7 : X-ray Profile of SE72/CyHe1Cp7POSS Blend (20 wt% POSS loading)

138

 

110000
Vle7POSS

_SE72/Vle7POSS(20%)

Intens1ty
8 8'

:5“:

-II—

 

 

 

 

10000. . I H ' . 1
5 10 15 20 25 30

 

‘ ““‘ STlIsobu7POSS

QF‘TNQ’I‘I IcnhnMQQI’flW/I.

 

 

 

20

Figure 5.9: X-ray Profile of SE72/STlIsobu7POSS Blend (20 wt% POSS loading)

139

 

é

-- Styrenylllsobu7POSS
__ SE7yStyrenylllsobu7POSS(20%)

.3

IIfIIITIITIIITIIIIIIIITIT TI

Inteésnyg q

s

_L
fit

 

 

I l I I

5 10 15 20 25 30
2 0

Figure 5.10: X-ray Profile of SE72/Styrenylllsobu7POSS Blend (20 wt% POSS loading)

 

Figures 5.4 and 5.8 show that after IsobusPOSS and V1Cp7POSS
macromers blended with PDMS (SE72), they still retain the low 20-angle
diffraction peaks, which are similar to their corresponding neat POSS
macromers. However, the crystalline peaks at the high 20 diffraction
angles, as observed in the x-ray diffraction curves of the neat IsobugPOSS
and V1Cp7POSS macromers, disappear after they are blended with PDMS.
This indicates that after ISObUgPOSS and V1Cp7POSS macromers are
mixed with PDMS, only large scale ordered POSS structures are
developed in the blends, but no close packed POSS structures are formed.

As seen in Figures 5.5, 5.6, 5.9, and 5.10, ST1Cp7POSS,
Styrenylle7POSS, STlIsobu7POSS, and Styrenylllsobu7POSS macromers

show less ordered structures after blended with PDMS, indicating a higher

140

degree of compatibility with PDMS than CngOSS, V3POSS, IsobugPOSS,
CyHeleyPOSS, and Vle7POSS.

In summary, the X-ray diffraction studies of POSS/PDMS (SE72)
blends reveal that the less ordered POSS macromers have better

compatibility with PDMS than the ordered POSS macromers.

5.4 Thermal Stability of POSS/PDMS Blends:

Figures 5.11 to 5.19 are the TGA curves of CngOSS/SE72,
VgPOSS/SE72, IsobugPOSS/SE72, ST1Cp7POSS/SE72,
Styrenylle7POSS/SE72, CyHele7POSS/SE72, V1Cp7POSS/SE72,
STlIsobu7POSS/SE72, and Styrenylllsobu7POSS/SE72 blends (20wt%
POSS loading).

It can be seen in Figure 5.11 that the TGA curve of CngOSS/SE72
blend locates below the TGA curves of both the neat components. This
indicates that the blending of CngOSS and PDMS decreases the thermal
stabilities of both the neat components.

The TGA curves of IsobugPOSS/SE72 (Figure 5.13),
StyrenleCp7POSS/SE72 (Figure 5.15), CyHele7POSS/SE72 (Figure
5.16) and V1Cp7POSS/SE72 (Figure 5.17) blends show that at the early
stage of decomposition, these curves locate between the TGA curves of
their corresponding neat components, while, after a certain temperature,
the TGA curves of these blends fall below the TGA curves of their

corresponding neat components.

141

As shown

in Figures 5.11 and 5.19, during most of the temperature

range investigated, the TGA curve of the CngOSS/SE72 blend is below

the TGA curves

of both of the neat components, while the TGA curve of

Styrenylllsobu7POSS/SE72 blend is between the TGA curves of their

corresponding neat components. We can see from Figure 5.12 that the

thermal stability of the V3POSS/SE72 blend is between the thermal

stabilities of their neat components: below a temperature of 510°C, the

TGA curve of VgPOSS/SE72 blend is below the TGA curve of SE72 but

above that of the V3POSS macromer, while above 510°C, the TGA curve

of this blend is below of V3POSS macromer but above that of the SE72.

 

 

 

 

 

 

 

 

120
1:
371.56°C 95.00%
100 —— ___... _________ . o
3: 355.700C 95.m% \+\\2. 450.35 C 95.00%
\\ Residue:
80‘ \ 1; 5.644%
’6‘ \ (0.2824mg)
E0 60" ‘1‘ .
0 I Resrdue:
B ‘1 3; -0.04554%
40~ I (-0.009070mg)
‘\
\l
20“ II Residue:
gggoszsu-J \ 2: -0.07773%
- ' — " "' . -0.02196m
—— SE72/Cp81’OSS (20wt% )——-3 \-\_Q #7 ( g}
100 200 300 400 500 600 700
Temperature (°C)

Figure 5.11: TGA Curve of SE7WCpsPOSS Blend (20 wt% POSS loading)

142

120

 

 

 

 

    
      

 

 

I 32
280.52°C 95.00% 2:
100 _ ................... 450.35°C 95.00%
1: *'\ +\ .
‘2 128°C 95.007 '\ »_ _.. ‘ 2 Rem“:
80‘ 5 0 ‘7 3 ~~\ \ 1: 47.87%
I (4.763mg)
5: I \ Residue:
E 60‘ o 3; 13.46%
.3) 0.60 C 57.08%I (3.173mg)
B I.
404 II\ Residue:
I \, 2; 007773%
I \ 000219611119
20‘ vsposs---1 I. \‘4
I—--—-- SE72-«2 \
0 —- SE72/vspossem1---3 \_
100 200 300 400 500 600 700
Temperature (°C)

Figure 5.12: TGA Curve of SE72/V3POSS Blend (20 wt% POSS loading)

 

 

 

    
   
    
   
 

   

       
   

 

 

 

120
3:
267.97°C 95.00% 2:
100 “=\r --------------- Q450.35°C 95.00%
1267.58°C 95.00% \ \\
\
80‘ \I \ Residue:
... . \ 1; 5.357%
8". I I. (0.8623mg)
a 60- 1 I3 i .
'5 I 1 Resrdue:
3 - I 3: -0.04315%
\ I
40— - 320.34°C 36.79% ‘1 (”007475”)
\
I I Residue:
. ‘ ‘ . -0.07773%
20 Isobu8POSS---1 \ II 2' (002195“,ng
- - - — SE72-«2 , 1
O —— SE72/lsobuSPOSS(20%)X-BQI \\
50 150 250 350 450 550 650
Temperature (°C)

Figure 5.13: TGA Curve of SE72JIsobu3POSS Blend (20 wt% POSS loading)

143

The thermal stability behaviors of the ST1Cp7POSS/SE72 and
STlIsobU7POSS/SE72 blends, as shown in Figure 5.14 and 5.18, are of
more interest.

The ST1Cp7POSS/SE72 blend (Figure 5.14) exhibits higher
decomposition temperature than both of their neat components. Below 3
temperature of 580°C, the TGA curve of ST1Cp7POSS/SE72 is above both
the TGA curves of ST1Cp7POSS macromer and SE72. When the temperatures
are higher than 580°C, the TGA curve of the ST1Cp7POSS/SE72 blend falls
between the TGA curves of ST1Cp7POSS macromer and SE72. It is assumed
that this thermal stability improvement might be due to the chemical
reactions that occur between ST1Cp7POSS macromer and PDMS at elevated
temperature. The attachment of P088 cages to the PDMS polymer chains, as
a result of these chemical reactions, would then lead to the excellent thermal
stability of the ST1Cp7POSS/SE72 blend.

Thermal stability improvement is also observed in the
STlIsobu7POSS/SE72 blend. As shown in Figure 5.18, although below a
temperature of 490°C, the TGA curve of the STlIsobu7POSS/SE72 blend is
between the TGA curves of their neat components, when temperatures are in
the range of 490°C to 580°C, the TGA curve of the blend is above both the
TGA curves of the STlIsobu7POSS macromer and SE72, indicating that
STlIsobu7POSS/SE72 blend has a better thermal stability than both of the neat
components. After the temperature exceeds 580°C, the TGA curve of the blend

again falls between the TGA curves of the ST1Isobu7POSS macromer and SE72.

144

120

 

 

 

    

 

 

 

1 2:
450.35°C 95.00% 3.
100 " “‘“x 464 855C 95 007
1: 381.22°C 95.00% *‘K\ ' ' 0
\\ \

804 ‘ ‘ Residue:
A 1: 39.80%
‘3 (2.89lmg)
in 60‘
g 4 Residue:

3: 26.98%
4°“ \‘ \ (4.560mg)
\ \
‘\\ ll .
20‘ ST1Cp7POSS---l \ $6317??qu
— - — —- SE72----2 \ 2: d 02 9
—— - SE72/ST1Cp71>085(2w;6)---3 \ (- - 1 6mg)
0 V I ' I T l f l '\k I Y
100 200 300 400 500 600 700
Temperature (°C)

Figure 5.14: TGA Curve of SE72/ST1Cp7POSS Blend (20 wt% POSS loading)

 

 

 

 

 

 

 

120
4 3:
100 _ _ 386.13°C 95.00% 2;
1: 374.62°C 95.00% ---.‘~“+\";5°-35°C 95°07"
‘ \
80° Residue:
g : 32.32%
‘5: (3.062mg)
£0 60*
g Residue:
40* 0.09643%
(0.02910mg)
20_ Residue:
Styrenylle7POSS---l . -0-07773%
. _ _ — — SE72----2 (-0 02196mxg)
0 ___. - Slim/Styrenyl} Cp7P‘OSS('2r()C/Efi)---v3 . \r-.\_ 4‘ . .
100 200 300 400 500 600 700

Temperature (°C)

Figure 5.15: TGA Curve of SE72/Styreny11Cp7POSS Blend (20 wt% POSS loading)

145

 

 

 

  
  
   
   
 

 

 

 

120
3:
371.08°C 95.00% ,
100 ______ f _______ 2. o
l: 348140C 95.m% \‘l‘.\ +\\450.35 C 95.00%
\-\ \ Residue:
80" \ \\ 1: 3.931%
g \ \\\ (0.2682mg)
1:; 60~ \ \\ Residue:
'5 i \\ 3; 0.01867%
3 + i .‘ (0.003834mg)
4'0" \ \\
.. l
\ \ .
\\ Resrdue:
20‘ CyHele7POSS----1 ‘\ 2: '0-07773‘70
J _ _ _ _ SE72 _______ 2 ‘ (—0.02196mg)
—— SE72/CyHc 1 (‘p7 POSS(2()%‘)----3 .
0 I ' I . I fl I \'\L i I I
100 200 300 400 500 600 700

Temperature (°C)

Figure 5.16: TGA Curve of SE72/CyHe1Cp7POSS Blend (20 wt% POSS loading)

 

 

120
J 3:
100 _ 392.08°C 95.00% 2.
1: 369.05°C 95.00% WC“~+\450.35°C 95.00%
i \ \\
\ ‘ \
80‘ -. \ .
\i“ \ Resrdue:

Weight (%)
$

 

 

      
   
 
 

\ 1; 20.50%
‘ (2.488mg)

‘ Residue:

 

 

404 3: 0.1279%
(0.03607ng

i

204 ' Residue:

Vle7POSS---l \ x . .o.07773%

J___- SE72-«2 -\ \ 2- (-0.02196rr1g)
o ___. SE72/Vle7POSS(2()%)---3 -\\,_J

100 260 300 460 560 660 700

Temperature (°C)

Figure 5.17: TGA Curve of SE72/V1Cp7POSS Blend (20 wt% POSS loading)

146

 

120

 

 

 

   
 

 

 

2:
379.82°C 95.00% 1‘
100 ——-\ 450.35°C 95.00%
32 284.96°C 95.00%
801 Residue:
A 3: 10.50%
§ i (0.9043mg)
En 60‘
é) Residue:
' 2: 1.750%
40. (0.4905mg)
Residue:
20* ____ SE72----l ‘ 1. -0.07773%
, _- SE72/ST]lsobu7POSS(2()‘FL)---2 \ ' (0.02196mg)
STlIsobu7POSS----3 \ L1
0 I ' T ' ' \¥ I
100 200 300 400 500 600 700
Temperature (°C)

Figure 5.18: TGA Curve of SE72/STlIsobu7POSS Blend (20 wt% POSS loading)

 

 

 

 

 

 

 

120
3:
307.24°C 95.00% 21
100 ---- ------------ + 450.35°C 95.00%
- l: 301.20°C 95.00% -\,_\ \\
.\\ \
804 °\_ \\ Residue:
,3 \ \\ 1: 3.605%
g, 60 \ \\ (0.6437mg)
.. l
g 3‘. 2‘\\ Residue:
B \. 1‘ 3; 1.971%
40‘ \ \\ (0.5486mg)
\ ‘1
\ “ Residue:
20- . ‘\ 2: -0.07773%
giggnyllésobfiPOSS-nl _\ ‘\ 00.02196ng
-——- SE72/Styrcnyl l lsobu7POSS( 209?)"-
100 260 360 460 700
Temperature (°C)

Figure 5.19: TGA Curve of SE72/Styrenylllsobu7POSS Blend (20 wt% POSS loading)

147

In summary, the TGA results reveal that only when POSS
macromers with the proper reactive corner groups (such as a styryl
group), induce chemical reactions between POSS and PDMS, will there be
a significant enhancement of the thermal stability of the POSS/PDMS
blends. The attachment of POSS massive cages to polymer chains renders

POSS/PDMS blends with excellent heat resistance.

5.5 Rheological Behavior of POSS /PDMS Blends:
5.5.1 Effects of POSS Macromers on the Rheological Behaviors of PDMS:

Figure 5.20 shows the storage modulus of the various POSS/PDMS
blends, versus angular frequency, at 30°C.

We can see from Figure 5.20 that the addition of CngOSS,
V1Cp7POSS, and ST1Cp7POSS macromers into PDMS (SE72) increases the
storage modulus of the PDMS, while, the storage modulus of
CyHele7POSS/SE72, IsobugPOSS/SE72, Styrenthp7POSS/SE72,
VgPOSS/SE72, STlIsobu7POSS/SE72, and Styrenylllsobu7POSS/SE72
blends are similar to that of the SE72.

The above results indicate that the addition of POSS into PDMS
doesn’t significantly increase the storage modulus of the polymer. It is
assumed that because there is no favorable interaction between these two
components, POSS macromers behave like inert fillers which have no

reinforcement to the polymer.

148

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149

5.5.2 Gelation Process of POSS/PDMS Blends:

This section describes the gelation phenomenon of POSS/PDMS
blends, which was discovered during the rheological measurements under
elevated temperature. Gelation of the POSS/PDMS blends results in a
rheological behavior change from that of a viscous liquid to that of an

elastic solid.

5.5.2.1 Background of Gelation:

The term “gelation” is used here to describe the conversion of a
liquid to a disordered solid by the formation of a network of chemical or
physical bonds between the molecules or particles composing the liquid.
In different situations, scientists use different terms to describe this
phenomenon: such as association, cross-linking, vulcanization,
flocculation, agglomeration, aggregation, clumping, or thickening.

Physical gelation occurs as a result of intermolecular association.
Intermolecular associations are weak bonds produced by Van der Waals
forces, electrostatic attractions, or hydrogen bonds. Chemical gelation
takes place as a result of chemical bonds, which are covalent attachments
between two atoms. Both physical gelation and chemical gelation lead to a
formation of a network in the system, rendering a rheological property
change from that of a viscous liquid to that of an elastic solid.

There are two major categories involved in gelation: polymeric

gels, and particulate gels.

150

Polymeric Gels: Polymeric chemical gel is formed when a precursor
liquid, composed of either small molecules or polymers, is cross-linked to
form a gel, as occurs for example, during the curing of elastomers and
thermoset plastics. Polymeric physical gelation is formed as a result of
any one of the following interactions: locally helical structures whereby
one molecule winds around another; microcrystallites; or nodular domains
in which the chain is chemically heterogeneous, and association occurs
only at preferred sites along the chain.

Particulate Gels: Particulate gelation is the conversion of an
initially stable sol composed of colloidal particles to a solid-like gel
phase by the formation of a network of particles. It occurs as a result of
intermolecular association, which draws particles into near contact,
producing a filler network. It has been postulated that the mechanical
behavior of a filled blend material in response to the applied deformation
is dominated by the formation, maintenance, and destruction of the filler
network.

In filled polymer compounds, because of the high viscosity of
polymers, filler particles dispersed in the polymeric matrix are in a
relatively stable state. It is assumed that the reinforcement of elastomers
due to reinforcing fillers (such as carbon black, fumed silica) is due to a
formation of network structures among filler aggregates and the polymeric
molecules. The network is held together by filler-filler interactions and

filler-polymer-filler bridge bonds between the filler aggregates. Long

151

polymer molecules that are strongly adsorbed to the particle surfaces can
induce gelation by bridging the gap between neighboring particles. The
rheological properties of mixtures of particles and adsorbing polymers
bear a resemblance to those of polymeric physical gels, wherein the
particles play the role of cross-linkers, binding different polymer
molecules together.

It has been found that appreciable carbon black gelation occurred in
filled rubber stocks during storage or vulcanization in the absence of
shear [°9' 7°]. The carbon black aggregates in the polymer matrix tended to
agglomerate, and at high concentrations it was hypothesized that they
form a continuous filler network structure, which was held together by
relatively weak Van der Waals forces. Additionally, it was observed that
these network structures broke up with increasing dynamic strain
amplitude. The dissociation of the filler structure, also called the Payne
effect, resulted in the removal of a significant part of the filler
reinforcement, leading to a drop in the storage modulus G’. Furthermore,
with the removal of the applied strain, the network was at least partially
restored.

Fumed silica is widely used in industry as an active filler for
reinforcement of elastomers, as a rheological additive in fluids, and as a
free flow agent in powders. Fumed silica reinforced polydimethylsiloxane
(PDMS) polymers have been extensively studied by scientists. Since its T8

is —123°C, PDMS is amorphous/rubbery at ambient temperatures and

152

above. When cross—linked, PDMS has a tensile strength of only about 0.35
MPa, hence it requires reinforcement to exhibit useful mechanical
properties. [°8] Amorphous silica, particularly fumed silica, is the primary

“’8' 7" 72] showed

reinforcing filler used in silicone elastomers. Studies
that the silanol groups and strained Si-O-Si bonds on the surface of fumed
silica interact with the terminal chain silanol groups and the ~(CH3)zSi-O-
Si(CH3)2- segments of the PDMS chains to form hydrogen bonding and
Van der Waals forces. It is believed that the intermolecular interactions
between fumed silica particles and PDMS render the formation of the
silica-PDMS network and is responsible for the reinforcement effects. The
network is held together by silica-silica interactions and silica-polymer-
silica bridge bonds between the silica aggregates. Increasing the silica
loading, surface area, and structure level increases the number of
interactions and hence the network strength.

One common problem in the studies of filled polymer gelation is
reproducibility. Because these gels are disordered materials that are
kinetically frozen, the method of preparation strongly influences the
properties obtained. As a result, reproducibility is often a major problem
with such materials; for example, the sample can “age”, or change slowly
over time. Therefore, the rheological properties of filled polymeric gels

are, on the whole, not yet well-understood, in part because of their

sensitivity to preparation and poor reproducibility.

153

Gelation phenomenon also has been observed in POSS/PDMS
blends. In this study, we examined the rheological property changes
during the gelation process of POSS/PDMS blends, the rheological
behavior of the gelled POSS/PDMS blends, and the influence of POSS
types, POSS concentration, polymer molecular weight, and annealing
temperatures on the kinetics of the gelation process. Based on the
experimental results, the gelation mechanics of the POSS/PDMS blends is
postulated. During the entire experiments, the sample preparations were

kept controlled at the same conditions as much as possible.

5.5.2.2 Gelation Process of POSS/PDMS Blends:

Figure 5.21 shows that the storage modulus, loss modulus and loss
tangent (tanfi) changes of IsobusPOSS/SE72 (10wt% POSS loading) before
annealing and after 60hr annealing at 200°C. We can see from Figure 5.21
that the storage modulus of the un-annealed IsobugPOSS/SE72 blend has a
crossover with its loss modulus, while this crossover disappear in the
annealed IsobugPOSS/SE72 blend: the storage modulus of the annealed
blend is higher than its loss modulus. It is also found that the loss tangent
(tan8) of the annealed IsobugPOSS/SE72 blend is lower than that of the
un-annealed IsobusPOSS/SE72 blend, and their values are less than 1.
These results indicate that the rheological behavior of the
IsobugPOSS/SE72 blend changed from that of a viscous liquid to that of

an elastic solid after annealing.

154

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155

The whole annealing process of the IsobusPOSS/SE72 blend (10wt%
POSS loading) is shown in Figure 5.22, which describes the gradual changes of
storage modulus (G’), loss tangent (tanS), and complex viscosity of the blend
with annealing time at 200°C. As shown in Figure 5.22 (a), with annealing time
the storage Modulus (G’) gradually increases and becomes less frequency-
dependent. Furthermore, the changes of G’ in the low frequency range are more
dramatic than those in the high frequency range. At the high frequency end, G’
remains basically constant after an initial drop at the beginning of the
annealing. This indicates that the during the annealing process, the large-scale
chain architecture of the polymer chain changes over annealing time, which has

a profound effect on the storage modulus in the low frequency range.

 

 

 

 

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Angular Frequency (rad/s)
a.Storage Modulus

Figure 5.22: Rheological Properties Changes of the 10weight % Loading
IsobugPOSSISE72 Blend with Annealing Time at 200°C (cont’d)

156

 

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c. Complex Viscosity

Figure 5.22: (cont’d)

157

The loss tangent and the complex viscosity behaviors of the
IsobugPOSS/SE72 blend with annealing time, as shown in Figure 5.22 (b)
and (c), manifest that the loss tangent of the blend drops with annealing
time and after 50 hrs, tan5 is less than 1, while the complex viscosity of
the blend becomes more frequency-dependent with annealing time.

The rheological experiment of PDMS (SE72) was also conducted
(Figure 5.23). The annealing of PDMS (SE72) sample at elevated
temperatures showed no modulus increase; instead the modulus of SE72
decreases with annealing time at 200°C. It is believed that this reduction
in modulus is caused by the thermal degradation of PDMS

macromolecules at elevated temperatures.

 

    

 

 

 

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Angular Frequency (1/s)
Figure 5.23: Comparison of the Storage Modulus (G’) and Loss Modulus (G”), as
a function of frequency, of PDMS (SE72) at different annealing time at 200°C

158

All of the previous results indicate that gelation occurs in the
IsobusPOSS/SE72 blend (10wt%POSS loading) under elevated
temperatures, which leads to the rheological behavior change of the blend
from liquid-like to solid-like. No gelation found in SE72 manifests that the

gelation of the IsobugPOSS/SE72 blend is caused by the addition of POSS

macromer.

5.5.3 Rheological Properties of Gelled POSS/PDMS Blends:

Figures 5.24 (a), (b) and (c) are the modulus, loss tangent, and
complex viscosity, as a function of frequency, of the un-gelled and gelled
IsobugPOSS/VisclOOM blend (10wt% POSS loading) at 30°C. These
figures show that the gelled POSS/PDMS blends have the rheological
features of “solid-like” materials.

Before the gelation, the storage modulus of the blend has a
crossover with its loss modulus (Figure 5.24(a)). After the network is
formed, the storage modulus of the blend is higher than its loss modulus
and the elastic storage modulus, G’, is less frequency dependent over a
wide range of frequencies, which suggests that even for long-time-
relaxation (or terminal) regions, the gelled blend behaves elastically.

As noted in Figure 5.24(b), the loss tangent of the gelled blend is
lower than that of the un-gelled blend, and their values are less than 1,

which is the characteristic behavior of a solid-like fluid.

159

 

 

 

 

 

 

 

 

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Figure 5.24: Comparison of Rheological Properties, as a function of frequency, of
un-gelled and gelled IsobugPOSS/V isc100M (10wt%) blend at 30°C (cont’d).

160

 

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c. Complex Viscosity
Figure 5.24: cont’d

As shown in Figure 5.24(c), the complex viscosity of the gelled blends
is more frequency dependent. The viscosity of the gelled blend falls off
greatly with increasing frequency. In the low frequency range, the gelled
blend has much higher viscosity than the un-gelled one. However, near the
high frequency end, it approaches the un-gelled blend, whose viscosity is
low and nearly constant throughout the frequency range.

In addition, the rheological properties of the gelled POSS/polymer
blends show more non-linearity than the un-gelled blends. Figure 5.25
shows the low-frequency modulus, versus strain, of
IsobugPOSS/VisclOOM (10wt% POSS) before and after gelation.

Compared to the un-gelled IsobusPOSS/VisclOOM blend, the gelled blend

161

exhibits an earlier drop at a smaller strain of 40%. The modulus of the
gelled blend tends to be highly strain-dependent, with linear behavior

confined to a low strain amplitude.

 

 

 

 

 

9.0E+04
30°C, F :62.91/ 10Hz

8.0E+04 « mummy S( )
NE 7.013404 :W
S
E 6.0E+04 ~
in 5.0E+O4 .
g 4.013404 . —Before Gelation
8 +After Gelation
2 3.0E+04 .
a.
g 2.0E+O4 -
G

1.0E+04 —

0.0E+00 T .

1 10 100 1000

Strain (%)

Figure 5.25: Storage Modulus, as a function of strain, for un-gelled and
gelled IsobugPOSSlVisc100M blends of 10Wt% POSS loading. The
experiment was performed at 30°C and with angular frequency of 62.9 lls.

Furthermore, the gelled POSS/PDMS blends are more creep
resistant than the un-gelled blends. Figure 5.26 is the strain, versus time,
of Visc30M/Isobu3POSS blend (20wt% POSS) under shear stress of 500Pa
at 30°C. During the creep phase, the strain of the un-gelled blend
increases with time at a nearly constant rate, while the strain of the gelled
blend, which is much lower than the strain of the un-gelled blend, is

independent of time after loading. During the creep recovery phase, the

162

strain of the un-gelled blend exhibits no recovery upon unloading, while
the strain of the gelled blend goes immediately to nearly zero with
unloading. The above creep results imply that the un-gelled blend behaves
like a Newtonian liquid, and the gelled one bears the features of Hookean
solid. We think that this high creep resistance behavior of the gelled
POSS/PDMS is a result of POSS macromers acting like anchors, which

constrain the mobility of the polymer chains.

 

1.0E+07 :

1.0E+06 E Un-Gelled Blend
1.0E+05 E /E_'_’
: Creep

1.0E+04 E I
Creep—“F Recovery
1.0B+03 -

v1.013+02 —
'§1.01~:+01 Gelled Blend
”1.03.00 1»
1.013-01 -
1.0E-02 g Creep
1.05.03
1.0E-04 ; T I

0.01 0. l 1 10 100
Time (min)

 

‘70)
THU!" WWW"!

 

l
v

 

Creep
Recovery

Tlllfll l Tl

 

 

 

 

Figure 5.26: Creep Behavior of the un-gelled and gelled IsobusPOSS/Visc30M
(20wt% POSS) blends. The experiment was conducted at 30°C, and shear
stress of 500Pa.

163

5.5.4 Physical Nature of POSS/PDMS Gelation:

As we mentioned before, gelation can be physical (which occurs as a
result of intermolecular association), or chemical (which takes place as a
result of chemical bonds). Both physical gelation and chemical gelation
lead to a formation of a network in the system, rendering a rheological
property change from that of a viscous liquid to that of an elastic solid. The
question here is: “What is the nature of the POSS/PDMS gelation: physical
or chemical?” Through the investigations in the following experiments, we
conclude that the gelation of the POSS/PDMS blends is physical.
5.5.4.1 DSC Result of POSS/PDMS Blend:

We expect that because the chemical composition of SE72 is polydimethyl
silicone (PDMS), it is unlikely that chemical reaction would occur between
POSS and PDMS. The DSC result of the IsobugPOSS/SE72 (20wt% POSS
loading) blend also proves that there is no chemical reaction between the two
components. Although, as shown later in Figure 5.37, the rheology test manifests
that the IsobugPOSS/SE72 blend (20wt% POSS) gels after 6 hours at 200°C,
however, the DSC result (Figure 5.27) of this blend, which was heated under
isothermal condition (200°C) for 6 hours, shows that no chemical reaction was
detected. In addition, the TGA result of Isobu3POSS/SE72 blend (20 wt% POSS
loading), as shown previously in Figure 5.13, also indicated that there is no
chemical reaction occurred in the blend under elevated temperatures. Therefore,
based on the above analysis, we suggest that the structure change in the

POSS/PDMS blends is a physical association between the two components.

164

 

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Figure 5.27: DSC Result of IsobugPOSS/SE72 (20wt% POSS
Loading) Blend under 200°C Isothermal Condition for 6hr.

5.5.4.2. Creep Tests --- Gelation Destruction and Re-forming of the
Gelled POSS/PDMS Blends

Because physical gelation occurs as a result of intermolecular
associations, which are weak Van der Waals forces and hydrogen bonds, it
can be destroyed by large stress or strain and re-formed at gelation
conditions. In the next experiment, the creep test is used to prove this
physical nature of the POSS/PDMS gelation.
l. Destruction of POSS/PDMS Gelation:

The behavior of a sudden decrease in viscosity above a critical shear
stress is often referred to as yield, and the critical stress is called the yield
stress. In a filled polymeric gel, the yielding of the gel is related to the

destruction of the filler-filler and/or the filler-polymer network.

165

In this study, creep tests were used to determine the yielding of
POSS/PDMS blends. Creep tests are useful for detesting the yielding of a
material, since if the imposed stress is below the yielding point, the steady-

state shear rate will be zero.

 

 

 

 

 

1.0E+01
E 30°C
€109.00 ...... mm)
,3 —x—J(10Kl>a)
3 1.0501
“:5
8 1.01:,02
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O.
3.3»
0 row 1
l.0E’05| l L ILAL‘Lf 1 1 lllllllr 1 1 lLLlll
1 10 Tum (8) 1(1) NIX)

Figure 5.28: Creep Compliances of gelled IsobugPOSS/Visc30M (10 wt%
POSS loading) Blends under shear stresses of 5 and 10 KPa at 30”C

Figure 5.28 shows the creep compliances of the gelled
IsobugPOSS/Visc30M (10wt% POSS) blend under constant shear stresses of
SKPa and 10 KPa respectively, at 30°C. Under a shear stress of SKPa, the
creep compliance of the gelled IsobugPOSS/Visc30M blend remains
constant, however, under a lOKPa shear stress, the creep compliance of

the gelled blend increases dramatically after 90 seconds.

166

 

1000;

 

 

 

 

 

E 30°C I!"
100 +5KPa Creep Test

+10KPa Creep Test

:2 10E

c E

3 .

52 1

a E

_g E

m 0.1 E

0.01 E
E
0001 L 1 1 1 W

1 10 Time (s) 100 1000

Figure 5.29: Shear Rate of Gelled IsobugPOSS/Visc30M Blends (10wt% POSS
loading) during creep test (under shear stresses of 5 and 10 KPa at 30°C)

l.E+11 n?

 

1m 1 TI!

1.E+10 —
1.E+09 ~ _5

 

 

ITIW" I 1”]

1.E+08
1.E+07 E
1.E+06 E

Viscosity (cP)

l .E+05 "E 300C

 

1'E+04 E + SKPa Creep Test

1.E+03 x 10KPa Creep Test

Ila-+02 l 1 1111111 1 1 l llLLll
l l
I

l 10 100 1000
Time (s)

 

 

 

Figure 5.30: Viscosity, versus time, of Gelled IsobusPOSSlVisc30M Blends (10wt%
POSS loading) during creep test (under shear stresses of 5 and 10 KPa at 30°C)

167

During the 5 and 10 KPa creep tests, changes of shear rate and
viscosity were also observed (Figure 5.29 and Figure 5.30). The results
show that under the SKPa shear stress, the shear rate of the gelled
IsobugPOSS/Visc30M blend retains zero, and its viscosity remains
constant; while under the 10KPa shear stress, the shear rate of the gelled
blend is no longer zero, and the viscosity has a sudden decrease. All the
above results indicate that yielding of the gelled IsobugPOSS/Visc30M
blend takes place during the 10KPa creep test.

The frequency sweeps of the gelled IsobugPOSS/Visc30M blends before
and after the 5 and 10 KPa creep tests were also conducted. Figures 5.31 and
5.32 are the modulus of the gelled IsobugPOSS/Visc30M blends (10wt% POSS

loading) before and after the creep tests of SKPa and 10KPa, respectively.

 

   

 

 

 

1.0E+05 E
: 30°C
"5
E
%‘
j; 1.0E+04 ‘t
2 ..
:3 .
B C
2 +G'(before creep)
+G"(before creep)
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+ G"(after creep SKPa)
1.0E+03 * 1“““l 111w“, l 1mm, 1 ”my.
0.1 1 10 100 1000
Angular Frequency (rad/s)

Figure 5.31: Modulus Comparison of the Gelled IsobugPOSS/Visc30M Blend
(10 wt% POSS loading) before and after the 5 KPa creep test

168

As shown in Figure 5.31, the modulus measured after the SKPa creep
test is almost coincident with the modulus before the creep test. It is also
noticed that after the SKPa creep test, the storage modulus of the blend still
remains greater than its loss modulus, which indicates that the network
structure is not destroyed by the shear stress.

Figure 5.32 shows that the un-crept IsobugPOSS/Visc30M gel blend has .
the rheological features of an elastic solid, where the storage modulus is
higher than its loss modulus. While the crept IsobusPOSS/Visc30M blend
behaves like a Newtonian liquid. The storage modulus of the blend measured
after the 10KPa creep test has a crossover with its loss modulus. This result
implies that the gelled blend has gone through a dissociation process during
the 10KPa creep test, leading to the rheological behavior change of the gel

from an elastic solid to a viscous liquid.

 

 

 

 

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: 3 ’57::Zé-
...---::223 ")“t
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1.0E+01 ‘ l “”“l l 1““‘l l ”Hung lAme
0.1 l 100 1000

10
Angular Frequency (rad/s)

Figure 5.32: Modulus, as a function of frequency, of Gelled
IsobugPOSS/ViscBOM Blends (10wt% POSS) before and after the 10 KPa creep

169

2. Re-Gelation Process:

When placing the destroyed IsobusPOSS/Visc30M blend (10wt%
POSS) at an elevated temperature of 200°C, the POSS-PDMS network can
be restored (Figure 5.33). The re-gelation process is very fast; it even
occurs during the heating phase. The storage modulus of the
IsobugPOSS/Visc3OM blend is already higher than its loss modulus upon
reach 200°C. This effect is probably because the destruction of the

gelation is partial, and the POSS/PDMS blend needs less time to gel.

 

 

 

 

1.0E+05 :
i 200W
NA _ o;".’:::’:.
ELOE+O4~E m, .
E E c;::;;::233°" “
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3 _
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_l-
21.OE+03
—o— G'(Ohr) + G" (0hr)
+ G'(4hr) + G" (4hr)
1.0E+02 . 1“”‘4l 11111”, 1mm. L rum.
0.1 l 10 100 1000

Angular Frequency (rad/s)
Figure 5.33: Re-Gelation of IsobusPOSS/Visc30M Blend (10wt% POSS) at 200°C

Figure 5.34 shows the modulus, versus frequency, of the re-gelled
IsobugPOSS/Visc30M blend (lOwt % POSS) at 30°C. Compared to the G’,

and G” curves before re-gelation (the curves with filled symbols as shown

170

in Figure 5.32), the re-gelled blend has the rheological features of an

elastic solid: its storage modulus G’ is higher than its loss modulus G”.

 

 

 

 

 

1.0E+05 ,
NE
E
'5‘
:1.0E+044t
= :
E t
O
z c
1.0E+03 . 3....” . ++um, . remap .
0.1 1 10 100 1000

Angular Frequency (rad/s)
Figure 5.34: Modulus, as a function of frequency, of Re-gelled
IsobusPOSS/Visc30M Blend (10wt% POSS) 30°C.
3. Discussion:

The above results indicate that yielding of the gelled POSS/PDMS
blends takes place during the 10KPa creep test, which reflects a
dissociation process of the POSS/PDMS gels. The yielding mechanism of
the gelled POSS/PDMS blends during the creep test is described as
follow: Imagine that a POSS/PDMS gel is subjected to a shear stress that
homogeneously displaces the particles and polymer chains from their
positions of static equilibrium. Pairs of POSS aggregates, and pairs of

POSS-PDMS would be pulled apart by this stress, and the separation

171

distances among the POSS aggregates and polymer chains would
increase. A force would be produced by this increased separation
between the POSS particles and the adsorbed polymer chains that would
tent to restore the original inter-particle spacing if the shear stress were
removed. In this case, the gel would maintain its mechanical stability.
But if the stress exceeds a certain point, any further stress would
produce a decreasing force, and the POSS-PDMS network structure
would break apart. This stress limit corresponds to the point of yielding.

Results of the creep tests (Figure 5.28) reveal that under the SKPa
yield stress, the creep strain of the gelled POSS/PDMS blends retains
constant (independent of time after loading), which indicates that the
gelled blends behave like a Hookean solid, and the associations between
the POSS and the adsorbed PDMS chains are not destroyed. Under the
10KPa yield stress, the gelled POSS/PDMS blend responds elastically in
the beginning (about 90 seconds). During this period, the POSS and
PDMS polymer chains, which are confined in the gel network and
entangled by surrounding chains, equilibrate in the deformed state. As a
result, the creep strain retains a basically constant value. However, when
the POSS and PDMS chains begin to relax locally and the polymer
chains extricate themselves from the constraining POSS particles and
mesh of surrounding chains, the POSS-PDMS network breaks down.

Consequently, as shown in Figure 5.28, the strain increases dramatically.

172

When the destroyed POSS/PDMS gel is placed under an elevated
temperature, the POSS-PDMS network structure is re-formed (Figure

5.33).

5.5.4.3 Physical Nature of the POSS/PDMS Gelation:

The above DSC and creep tests show that the gelation of the
POSS/PDMS blend is physical. No chemical reaction is observed during
the POSS/PDMS gelation process. The associations between POSS and
PDMS are weak Van der Waals forces, and they can be destroyed by
large stress or strain and re-formed at elevated temperatures.

The detail gelation mechanism will be discussed later in 5.5.6.1.

173

5.5.5 Effects of Compositions and Experimental Conditions on the
Gelation Processes of the POSS/PDMS Blends:

In the following text, the effects of the POSS chemistry, POSS
loading, PDMS molecular weights and annealing temperatures on the
gelation rates of the POSS/PDMS blends are discussed.

First, we need to define a parameter which can properly

characterize the gelation rates of the POSS/PDMS blends.

5.5.5.1 Rate of Storage Modulus Change (Ran-Characterization of
the Gelation Rates of the POSS/PDMS Blends:

Because the gelation process of a POSS/PDMS blend is affected by
the chemistry of the components, the composition and the experimental
conditions etc., it is necessary to find a parameter that defines the
gelation rate of the blend. Since the storage modulus of the POSS/PDMS
blend in the low-frequency range changes dramatically with annealing
time during its association, the rate of storage modulus change (in the low
frequency range) --- R0, is used to characterize the gelation rate of the
POSS/PDMS blend.

The Rate of Storage Modulus Change (R5) is defined as:

G’t,T -G’O,T
R6“): ( )t < )

 

where t is the annealing time; G’(t, T) is the storage modulus of the blend
at annealing time t and annealing temperature T under a constant

frequency f; and G’(O, T) is the initial storage modulus of the blend at

174

annealing temperature T under a constant frequency f. In this study,

angular frequency f is chosen as l rad/s.

5.5.5.2 Effects of the POSS Chemistry on the Gelation Processes of the
P088] PDMS Blends:

Figure 5.35 is the rates of storage modulus change (R0) of the
blends of PDMS (SE72) with POSS macromers bearing different corner
groups (20wt% POSS loading).

We can see from Figure 5.35 that among the three R3POSS
macromers: CngOSS, V3POSS, and IsobugPOSS, gelation occurs in the
IsobugPOSS/SE72 blend, but no gelations are found in the CngOSS/SE72,
V8POSS/SE72 blends.

Although there is no gelation in the CngOSS/SE72 blend, however,
with one of its cyclopentyl corner groups replaced, gelation takes place in
the blends of V1Cp7POSS ISE72, ST1CP7POSS ISE72, CyHeICp7POSS
ISE72, and Styreny11Cp7POSS/SE72. The order of gelation rates, from fast
to slow, is Styrenthp7POSS/SE72, CyHele7POSS/SE72, ST1CP7POSS
ISE72, and V1Cp7POSS/SE72.

Similar results can be arrived at when comparing the gelation rates
of the blends of SE72 with POSS macromers bearing isobutyl groups as
their corner groups. As shown in Figure 5.35, the gelation rates of the
Styrenylllsobu7POSS/SE72 and STlIsobu7POSS/SE72 blends are

significantly higher than that of the IsobugPOSS/SE72 blend. The order of

175

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176

gelation rates, from fast to slow, is StyrenylIIsobu7POSS/SE72,
STlIsobu7POSS/SE72 and IsobugPOSS/SE72.

We also notice that the gelation rates of POSS macromers with
isobutyl corner groups (such as: IsobugPOSS/SE72,
Styrenylllsobu7POSS/SE72 and STlIsobu7POSS/SE72) are higher than the
gelation rates of their corresponding POSS macromers bearing cyclopentyl
corner groups (for example: CngOSS/SE72, Styreny11Cp7POSSlSE72, and
ST1CP7POSS /SE72). The Isobu8POSS/SE72, Styrenyl1Isobu7POSS/SE72
and STlIsobu7POSS/SE72 blends gel faster than the CngOSS/SE72,
StyrenleCp7POSS/SE72, and ST1CP7POSS/SE72 blends, respectively.

The above results reveal that the chemistry of the organic corner
groups on the POSS cages has dramatic effects on the gelation rates of the
POSS/PDMS blends. It is thought that the compatibility between POSS
and PDMS, the dispersion of the POSS in PDMS and the interactions
between POSS and PDMS influence the gelation processes of the
POSS/PDMS blends.

Because of their good compatibilities with PDMS, IsobugPOSS,
Styrenylllsobu7POSS, STlIsobu7POSS, Styreny11Cp7POSS, ST1CP7POSS,
and CyHele7POSS macromers are well dispersed in the host and form
stable colloidal dispersions. At elevated temperatures, polymer chains
diffuse to POSS particle surfaces and form POSS-polymer associations.

However, since CngOSS and V3POSS macromers have relatively

poor compatibility with PDMS, these two POSS macromers are not well-

177

dispersed and have a larger domain phase in the PDMS matrix. This
severe aggregation of POSS macromers dramatically decreases the POSS
surface areas that polymer chains can interact with, leading to a less
effective use of the POSS macromers.

In summary, the gelation rates of the POSS/PDMS blends depend on
the chemistry and structures of the POSS corner groups. Our studies
manifest that POSS macromers which have good compatibilities with
PDMS have a stronger tendency to gel under elevated temperatures than
those with poor compatibility. Good compatibility ensures thorough
dispersions of the POSS macromers in the PDMS matrix and-sufficient
interactions between POSS and PDMS, which result in the formation of
POSS-PDMS network. While for POSS macromers which are incompatible
with the PDMS host, POSS-PDMS networks are less likely to form in the
blends because of the reduced interacting surfaces of the POSS

macromers.

178

5.5.5.3 Gelation Behaviors of POSS/PDMS Blends with Different POSS
Concentrations:

Figure 5.36 is the rate of storage modulus change (R3), versus
annealing time, of IsobugPOSS/VisclOOM blends with different POSS
loadings. The results show that with increasing POSS loading, the
gelation rates of the blends increase. It is assumed that increasing the
POSS concentration increases the number of anchors (interaction sites)

for polymer chains to interact with, and hence the gelation rates of the

 

 

 

blends.

6.0E+03 _ fl
7% F 50 wt%. 200°C
5 5.0131903 . —e—VisclOOM/Isobu8POSS(lO%)
g, . - +VisclOOM/Isobu8POSS(20%)
g 4.0E+O3 lE +VisclOOM/Isobu8POSS(30%)
a? r + Visc lOOM/Isobu8POSS(50%)
Q) _
g) 3.0E+O3 at
J:
U i
g .
3 2.0E+O3 —:
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“5 1.0E+03 —-
8 l-
52 20 wt% 10 wt%

ODE-14]) : .- : ; : ; : - : .. ‘ '3--:-°:'-: 3 -.- ;; -.~

0 200 400 600 800 1000 1200 1400
Annealing Time (min)

Figure 5.36: Effects of POSS Loading on the Gelation Rates of
IsobugPOSSl PDMS (V isc100M) Blends

179

5.5.5.4 Influence of PDMS Molecular Weight on the Gelation Rates of
POSS/PDMS Blends:

Figure 5.37 shows the effect of PDMS molecular weight on the
gelation rates of IsobugPOSS/PDMS blends (20wt% loading). Comparing
the gelation rates of the blends of IsobugPOSS with Visc3OM, Visc60M,
and VisclOOM, we can see that with increasing of PDMS molecular
weight, the gelation process slows down. Such an inverse dependence on
molecular weight or indirectly on viscosity would be expected in a
diffusion-controlled gelation process. Increasing the molecular weight of
PDMS enhances the entanglement of the polymer chains, hence reduces
the diffusion rate of the polymer chains towards POSS particles. However,
the gelation rate of the IsobugPOSS/SE72 blend is higher than those of the
IsobugPOSS/Visc60M and Isobu8POSS/VisclOOM blends. We assume that
it is because POSS macromers are better dispersed in the high molecular
weigh PDMS gum (SE72) than in the PDMS fluid (Visc), as stated in
Chapter 4. This dispersion effect ensures POSS macromers have more

surface areas that PDMS chains can interact with.

180

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181

5.5.5.5 Effects of Annealing Temperatures on the Gelation Rates of
POSS/PDMS Blends:

The rates of storage modulus change (R3) of IsobugPOSS/Visc3OM
(10wt% POSS loading) blends at different annealing temperatures are
shown in Figure 5.38. The results show that decreasing the annealing
temperatures results in an enormous drop in the gelation rates of the
POSS/PDMS blends. This phenomenon can be explained by realizing that
the annealing temperature has a tremendous impact on the diffusion rate
of the polymer chains. Raising the temperature increases the mobility of
the polymer chains by expanding the free volume and boosting the thermal
energy of the polymer chains. As a result, the diffusion rate of polymer

chains towards POSS macromers increases, leading to a faster gelation

 

 
 
  
  
 
  

 

process.

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8 .
5 :L

E .

o

B O

52 ~ 130C
0 ----------- : , . 1 ; . 1 1 1

 

 

 

0 500 1000 1500 2000 2500 3000 3500 4000
Annealing Time (min)

Figure 5.38: Effects of Annealing Temperatures on the Gelation Rates of
IsobusPOSSl PDMS (V isc30M) Blends (10wt% POSS Loading)

182

5.5.6 Discussion
5.5.6.1 Gelation Mechanism of the POSS/PDMS Blends

From the above rheological results, we can see that under elevated
temperatures gelation occurs in POSS/PDMS blends. The interactions
between PDMS and POSS macromers, which lead to the formation of
POSS-POSS or/and POSS-PDMS network, take place and progress further
upon aging (annealing) at elevated temperatures. The nature of these
interactions is physical, as stated earlier.

There are two possible physical interactions, which may contribute
to the network strength of the POSS/PDMS blends:

l) Interactions between POSS and POSS macromers, which lead to

the flocculation of the POSS macromer.

2) Interactions between POSS and Polymer, which result in POSS-

polymer associations.

In the first case, POSS particles, assumed well-dispersed in polymeric
matrix, diffuse toward each other to form particle pairs, triplets, and so on.
This growth process continues until filler network is formed. In this
situation, the domains of POSS aggregates after gelation would be bigger
than those of POSS aggregates before gelation, and there would be a
tendency toward larger phase separation. However, as shown in Figures 5.39,
and 5.40, the X-ray diffraction curves of the Styrylllsobu7POSS/SE72 and
Styrenylllsobu7POSS/SE72 blends (20wt% POSS loading) after gelation

shows little difference from the X-ray diffraction curves of these blends

183

 

é

 

 

 

; sr1tsobu7Possxs1~372 (before gelation)

2500 t — STlIsobu7POSS/81372 (after gelation)
2000—E
b l-
E1500~E
E :
100an
500%

0_ k
29

Figure 5.39: X-ray Diffraction Profiles of STlIsobu7POSS/PDMS (SE72) Blends
(20wt% POSS Loading) Before and After Gelation

 

 

 

 

2000 ,
1800 -*- Styrenylllsobu7POSS/SE72 (before gelation)
1600 —- Styrenylllsobu7POSS/SE72 (after gelation)
1400
3.1200
E1000
'5 800
600
400
CW 11+‘*‘+:'114:“‘1#+"‘n
5 10 15 20 25 30

20

Figure 5.40: X-ray Diffraction Profiles of Styrenylllsobu7POSS! PDMS (SE72)
Blends (20wt% POSS Loading) Before and After Gelation

184

before gelation, indicating that the gelled blends are still homogenous and
no phase separation occurs. Also it is observed that during the
experiments, the gelled Styrylllsobu7POSS/SE72, and
Styrenylllsobu7POSS/SE72 blends samples still remain transparent.
Therefore it is postulated that POSS flocculation is not the main gelation
mechanism of the POSS/PDMS blends.

In the second case, interactions, similar to those found in fumed
silica filled PDMS, occur between PDMS and POSS when the Si-O-Si
bonds on the surface of POSS particles interact with the —(CH3)ZSi-O-
Si(CH3)2- segments of the PDMS chains resulting in Van der Waals
interactions. Although the adsorptive interactions in POSS-polymer
blends are weak, there is, however, considerable evidence that the
elastomer molecules are affected by even weak interactions arising from
adsorptive or dispersion forces. As a result of these weak interactions
between filler and polymer chains, the molecular mobility of polymers is
decreased in the vicinity of filler surfaces [68’ 71’72].

It is postulated that long polymer'molecules are adsorbed to the
surfaces of POSS particles, inducing the formation of a gel network by
bridging the gap between the neighboring POSS particles. The bridging
can be a single polymer chain, which is attached to two or more adjacent
POSS aggregates, forming a POSS-polymer-POSS bond bridge (Figure

5.41(a)), or two single polymer chains entangle together, each of which

is attached to a different single POSS aggregate, (Figure 5.4l(b)),

185

A single polymer chain is attached to two or more adjacent
POSS aggregates, forming a POSS-polymer-POSS bond

Two single polymer chains entangle together, each of
which is attached to a different single POSS aggregate,

 

A single polymer chain, which is attached to a single POSS

 

(C) . _ _. f5. ._', aggregate, entangle with other free bulk polymer chains in
3 7 the system
. @DL
POSS Aggregate PDMS polymer chains

Figure 5.41: Schematic Diagram of the Formation of the POSS-PDMS Network

or a single polymer chain, which is attached to a single POSS aggregate
entangle with other free bulk polymer chains in the system (Figure
5.41(c)). The rheological properties of the mixture of POSS particles and
adsorbing polymers bear a close resemblance to those of polymeric
physical gels, wherein the POSS particles play the role of cross-linkers,
binding different polymer molecules together.

In summary, the gelation of the POSS/PDMS blends occurs as a
result of intermolecular associations between the POSS filler and polymer
chains, leading to the formation of a POSS-PDMS network. The
interaction between POSS and polymer chains is mainly due to Van de
Waals force. However, the precise nature and origin of the gelation

process for POSS/Polymer blends still needs further investigation.

186

5.5.6.2 Gelation Process of POSS/PDMS Blends:

In our study, the storage modulus change at the low frequency range
is used to characterize the gelation rate of the POSS/PDMS blend.
Although the gelation rates of POSS/PDMS blends vary with the
composition of the blends and experimental conditions etc., the gelation
process generally includes four stages, as shown in Figure 5.42: (1) an
induction period, (2) an acceleration stage, (3) a plateau stage, and (4) a
deceleration stage. Although the previous rheology tests show that some
POSS/PDMS blends exhibit virtually no induction period, while others
have little or no tendency toward slowing down or have a very short
plateau stage, most blends can clearly manifest all these four stages at

proper temperatures.

 

T-

_l

J

Induction Acceleration Plateau l Deoeleration

i \

 

Rate of Storage Modulus Change (RC)

 

 

 

T l T I

Annealing Tim:

Figure 5.42: Schematic Illustration of the Gelation Process
of POSS/Polymer Blends

187

The induction period represents the time interval, during which no
measurable gelation can be observed at the annealing temperature. During
this stage, polymer chains near the POSS aggregates diffuse further
toward the surfaces of POSS particles, but there are no interactions
formed between them. Following the induction period, gelation occurs at a
rate which is dependent on temperature and the nature of the composition.
In this stage, an embryo of POSS-polymer network forms and the storage
modulus of the blend dramatically increase. As the generation of the POS-
polymer network culminates, the rate of storage modulus increase reaches
a constant and the gelation process comes to a plateau period. After the
POSS-polymer network is mostly completed, the gelation process reaches
its deceleration stage. At this stage, the rate of modulus increase drops
and gelation process slows down.

The gelation processes of POSS/PDMS blends are affected by the
POSS chemistry, POSS loading, PDMS molecular weight, and annealing
temperatures. With increasing of the compatibility between POSS and
PDMS, POSS loading, and annealing temperatures, and decreasing of PDMS

molecular weight, the gelation rates of the POSS/PDMS blends increase.

5.5.7 Summary:
1. Rheological Features of Gelled POSS/PDMS Blends:

The rheological properties of the gelled POSS/PDMS blends bear the
features of elastic solids. The storage modulus G’ of the gelled blends is

higher than their loss modulus G”, and G’ is nearly independent of frequency.

188

For these solid-like POSS/PDMS gels, their loss tangent, tan®, is less than 1
and their shear viscosity decreases with increasing frequency.

In addition, the gelled POSS/PDMS blends display stronger nonlinear
rheological behaviors than the un-gelled blends. The storage modulus of the
gelled blends has an earlier drop at a smaller strain than the un-gelled blends.

Furthermore, the Gelled POSS/PDMS blends have significantly

improved creep resistance.

2.Gelation Rates of the POSS/PDMS Blends:

The studies of the effects of POSS chemistry on the POSS/PDMS
gelation reveal that the POSS—PDMS associations tend to occur in blends
_where POSS macromers are well dispersed in PDMS matrix, i.e. where POSS
macromers have good compatibility with PDMS. The gelation rates of the
POSS/PDMS blends are enhanced with increasing of the annealing

temperatures and POSS loading.

3. Gelation Mechanism of the POSS/PDMS Blends:

The gelation of the POSS/PDMS blends occurs as a result of
intermolecular association between the POSS filler and the PDMS chains,
leading to the formation of a POSS-PDMS network. The interactions between
POSS and polymer chains are mainly Van de Waal forces. The POSS-PDMS
network can be destroyed under large stress or strain and be re-formed at

elevated temperatures.

189

CHAPTER 6

CONCLUSIONS AND RECOMMENDATIONS

 

6.1 Conclusions:

In this study, POSS macromers were incorporated into polymeric
system by blending. Systematic studies on the POSS/polymer nanoscopic
materials were, for the first time, conducted. The results of this work are
concluded as follows:

1. The microstructures and thermal stability studies of POSS
macromers show that the morphologies and properties of POSS macromers
vary‘with the chemistry of the corner groups on the POSS cages.

a). Microstructural studies of POSS macromers by X-ray diffraction
show that the higher the symmetry and regularity of the POSS macromers,
and the smaller the size of the corner groups, the more ordered the POSS
macromers. Among the 12 POSS macromers investigated, CngOSS,
CngOSS, V3POSS, and Isobu3POSS are more ordered than PthOSS,
StyrenylgPOSS, ST1Cp7POSS, Styrenylle7POSS, CyHele-IPOSS,
Vle7POSS, STlIsobu7POSS and StyrenyllIsobu7POSS.

b). The chemistry of the organic corner groups on the POSS cages
plays an important role in determining the thermal stabilities of POSS
macromers. The POSS macromers with functionalities, which may
undergo chemical cross-linking reactions, possess high thermal stability,

for example: among all the 12 POSS macromers investigated, the

190

StyrenylgPOSS (Tdec: 458.18°C, Residue: 79.12wt%) and PthOSS (Taco:
487.97°C, Residue: 52.71wt%) macromers have significantly high
decomposition temperatures and residues.

The order of the POSS decomposition temperature from high to low
is: PthOSS (487.97°C), Styreny18POSS (458.18°C), CyBPOSS (397.5°C),
ST1Cp7POSS (381.22°C), Styrenylle7POSS (374.62°C), CpsPOSS
(371.560C), v,cp,Poss (369.05°C), CyHeICp7POSS (348.14°C),
Styrenyl1Isobu7POSS (301.2°C), STlIsobu7POSS (284.96°C), Isobu8POSS

(267.58°C), and vsposs (251.28°C).

The order of the POSS residue yields from high to low is:
Styreny18POSS (79.12wt%), PhsPOSS (59.71wt%), V8POSS (47.87wt%),
ST1Cp7POSS (39.80wt%), StyrenyIICp7POSS (32.32wt%), Vle7POSS
(20.50wt%), CysPOSS (l4.73wt%), STlIsobu7POSS (10.50wt%), CngOSS
(5.64wt%), Isobu8POSS (5.36wt%), CyHeICp7POSS (3.93wt%), and
Styrenyl1Isobu7POSS (3.6wt%).

c). The DSC results of the POSS macromers show that the chemistry
of the corner groups on POSS cages influences the transition temperatures
of the POSS macromers.

The melting temperatures of StyrenylgPOSS, IsobugPOSS, V3POSS,
CyHeleyPOSS and Styrenylllsobu7POSS macromers are 274.3°C,
272.1°C, 349.1°C, 339.1°C and 169.3°C, respectively. The melting peaks

of CngOSS, CngOSS, PthOSS, Styrenylle7POSS, ST1Cp7POSS,

191

V1Cp7POSS, and STlIsobU7POSS macromers are not observed because
their melting temperatures are higher than their decomposition
temperatures.

Weak associations are also observed in CngOSS, CngOSS,

StyrenylgPOSS, PthOSS, and Isobu8POSS macromers.

2. Morphological structures of POSS/PS and POSS/PDMS blends
were conducted by using TEM and X-ray diffraction. The results are
summarized as follow:

a). The morphology studies of POSS/PS blends by TEM show that
the chemistry of POSS macromers plays an important role in determining
the morphologies of the POSS/PS blends. Depending on the attached
chemical groups on the POSS macromer, the morphOlogies of POSS/PS
blends ranged from a complete phase separation between POSS and PS to
a homogeneous dispersion of POSS in the PS matrix in a nanoscopic
scale. Among the eight POSS macromers used, PthOSS is the most
compatible one with PS and can be homogeneously dispersed in PS
matrix. All other POSS/PS blends display a certain amount of phase
separation to a various degrees.

The POSS concentration and PS molecular weight also influence the
morphologies of the POSS/PS blends. With a decrease of POSS loading
and increasing of PS molecular weight, POSS macromers are more

homogeneously dispersed in the PS matrix.

192

b). The X-ray diffraction studies of POSS/PS blends show that the
crystallography of POSS macromers in the POSS/PS blends depends on
the compatibility between the two components. The more compatible
POSS and PS are, the less crystalline the POSS macromer becomes when
it blend with PS. When the two components are miscible, the POSS
macromer disperses homogeneously in the PS matrix. Among the eight
POSS macromers studied, PthOSS is the most compatible one with PS.
All the other POSS macromers: ST1Cp7POSS, StyrenylgPOSS, CngOSS,
CngOSS, VgPOSS, V1Cp7POSS, and CyHele7POSS are partially
compatible with PS.

With decreasing of POSS loading and increasing of PDMS
molecular weight, POSS macromers are more well-dispersed in the PS
matrix.

c). The morphology studies of POSS/PDMS blends by X-ray
diffraction show that the less ordered POSS macromers have better

compatibility with PDMS than the ordered POSS macromers.

3. Interaction studies of the POSS/PS blends show that there is no
favorable interaction between macromers and polymeric chains. The POSS
macromers behave like plasticizers in the PS matrix, which results in the
decrease of the glass transition temperature of the PS and the broadening

of the transition zone of the PS.

193

The more compatible between the POSS macromer and PS, the more
the Tg drops and the more the transition width broadens. Among the five
POSS/PS blends studied (CngOSS/PS, StyrenylgPOSS/PS, PthOSS/PS,

IsobUgPOSS/PS, ST1Cp7POSS/PS), the T8 of the PthOSS/PS blend is the

lowest.

4. Thermal stability studies of POSS/PS blends indicate that
POSS/PS blends exhibit improved thermal stability when using POSS
macromers with higher decomposition temperatures and residue yields
than PS.

Thermal stability studies of POSS/PDMS blends reveal that only
when POSS macromers with the proper reactive corner groups (such as:
styryl group), which induce chemical reactions between POSS and PDMS,
can significantly enhance the thermal stability of the POSS/PDMS blends.
The attachment of POSS massive cage to the PDMS chains renders

POSS/PDMS blends with excellent heat resistance.

5. The rheological investigations of POSS/PDMS blends show that
under elevated temperatures, a network forms between POSS macromers
and PDMS polymer chains, resulting in the gelation of the POSS/PDMS
blends. It is postulated that this gelation of the POSS/PDMS blends occurs
as a result of intermolecular association between POSS macromers and

PDMS polymer chains.

194

The formation of gelation between POSS and PDMS endows the
POSS/PDMS blends with a solid—like behavior. The gelled POSS/PDMS
blends have high modulus, and significantly improved creep resistance.
They also display stronger nonlinear rheological behaviors than the un-
gelled blends.

Because of its physical nature, the gelation formed in the
POSS/PDMS blends can be destroyed under large stain or stress and re-
formed at elevated temperatures.

The studies of the effects of POSS chemistry on the gelation of the
POSS/PDMS blends reveal that the associations tend to occur in blends
where POSS macromers are well dispersed in polymer matrix, i.e. where
POSS macromers have good compatibility with polymer.

It was also found that the gelation rates of POSS/PDMS blends are
enhanced with increasing of the annealing temperatures and the P088

concentrations.

In summary, the crucial parameters in developing POSS/polymer
nanoscopic materials with the desired properties are the compatibility and
interactions between the two components, which determine the
morphology and interface of the POSS/polymer blends. Good
compatibility and strong interactions between POSS macromer and

polymers result in a nano—dispersed POSS/polymer blend with an

195

 

enhanced performance, and these two requirements may be achieved by

selecting POSS macromers with desired functional corner groups.

6.2 Recommendations:

A lot of efforts have been put into the above investigations on the
POSS/polymer blends. However, since this research was just the
beginning exploration of POSS macromers as reinforcing fillers for
polymers, some of the structure/property relationships of POSS/polymer
blends were still not completely clear and fully understood. The author
suggests that the following further investigations should be conducted to

make the current research work more thorough and complete.

1. During the TGA experiments of POSS/PDMS blends, it was found that
ST1Cp7POSS/PDMS, and ST‘Isobu7POSS/PDMS blends exhibit
significantly improved thermal stability. We assumed this improvement is
due to the chemical reactions between POSS macromers and PDMS.
However, further inspections need to be done in order to prove the
mechanism of this improvement.

2. To develop POSS macromers as a reinforcing filler for silicone gum,
the mechanical properties of the POSS/PDMS blends, the effects of the
addition of curing agents in PDMS on the gelation of POSS/PDMS blends

and so on need to be examined.

196

 

3. Studies on the gelation of other POSS/polymer blends need to be
carried out in the future. Through these further investigations, we can find
out that if gelation occurs in other POSS/polymer systems and if these
POSS/Polymer pairs have the same gelation mechanism as the
POSS/PDMS blends.

4. The morphologies and properties (mechanical properties, flame
retardation, and oxygen permeability) studies of the blends of POSS
macromers with other types of polymers (for example: PP, PE, Nylon,
Epoxy, NR, EPR...) need to be investigated. Through these studies, we
can test if the structure/property relationships developed in this work
apply for other POSS/polymer systems.

5. Because the limited amount of POSS macromers available, this work
only studied the morphologies and properties of solution blended
POSS/polymer blends. The author suggests that the investigation of the
morphologies and properties of the mechanical blended POSS/polymer
blends (such as extruder, internal mixer) need to be conducted in the

future.

197

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