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This is to certify that the

thesis entitled

EFFECT OF PHENYL-FUNCTIONAB STRUCTURED SILANOL
ON THE NETWORK FORMATION OF
EPOXY-AMINE SYSTEMS

presented by

Madhu Namani

has been accepted towards fulﬁllment
of the requirements for

Master's degree in Chemical Engineering

 

 

Major professor

January 27, 2003

MS U is an Afﬁrmative Action/Equal Opportunity Institution

 

 

 

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6/01 cJClRC/DateDuopss-sz

 

EFFECT OF PHENYL—FUNCTIONAL STRUCTURED SILANOL
ON THE NETWORK FORMATION OF
EPOXY-AMINE SYSTEMS

By

Madhu Namani

A THESIS
Submitted to
Michigan State University
In partial fulﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

111
CHEMICAL ENGINEERING

Department of Chemical Engineering and Materials Science

2003

ABSTRACT
EFFECT OF PHENYL-FUNCTIONAL STRUCTURED SILANOL

ON THE NETWORK FORMATION OF
EPOXY-AMINE SYSTEMS

By
Madhu Namani

The type of R- group on trisilanol polyhedral oligomeric silsesquioxane (POSS)
(R7Si709(OH)3) can affect the acidity of the —OH group present. Trisilanol phenyl POSS
was found to be more acidic since the phenyl group on the silicon atom increased the
acidity of the silanol groupl. Based on the fact that acidic alcohol systems like phenol
accelerate the epoxy amine curing reaction, the effect of trisilanol phenyl POSS on the
curing kinetics of the epoxy amine reaction was studied on commercially available epoxy
resins like diglycidyl ether of bisphenolA, DGEBA and tetraglycidyl diamino diphenyl
methane, TGDDM with diamine terminated polypropylene oxide, Jeffamine D-23O and
2, methyl 1,5 pentadiamine, DytecA as curing agents. We observed a signiﬁcant increase
in the glass transition temperatures T8 for TGDDM amine systems containing trisilanol
phenyl POSS under low temperature curing conditions. Dynamic Mechanical Analysis
(DMA) was performed on cured epoxy amine samples containing trisilanol phenyl POSS,
varying from O to 1.0% and the glass transition temperature was determined from the
tan5 peak. Fourier Transform Infrared Spectroscopy (FTIR) experiments was used to
study the curing kinetics in epoxy amine systems with and without trisilanol phenyl
POSS. It was observed that the trisilanol phenyl POSS initially improves the rate of the
secondary amine reaction with the epoxy leading to increased consumption of amine and

epoxy, thereby forming a network having higher glass transition temperatures.

dedicated to my parents ..........

iii

ACKNOWLEDGEMENTS

I would like to express my sincerest thanks to my advisor, Professor Andre Lee
for his support, guidance, and leadership throughout my graduate education. In addition I
would like to thank Professor Krishnamurthy Jayaraman and Professor Michael Mackay
for serving on my Master’s Defense Committee.

I would like to thank Dr. Bruce Fu who helped me with my thesis work by giving
valuable suggestions and also assisted me in performing the Fourier Transform Infrared
Spectroscopy experiments.

I would like to thank Dr. Haddad of Air Force Research Laboratory, for providing
me with the NMR results of DytecA/ trisilanol phenyl POSS and Jeffamine D—230/
trisilanol phenyl POSS systems.

I would like to thank Dow Chemical for providing samples of DER332
(DGEBA), Huntsman Chemicals for Jeffamine D230 and DuPont Chemicals for
providing samples of DytecA.

Last, but not the least, I deeply thank my parents and family for their emotional

and ﬁnancial support and their never—endin g encouragement throughout my education.

iv

TABLE OF CONTENTS

List of Tables ...................................................................................... ..vii
List of Figures ..................................................................................... viii
CHAPTER 1
INTRODUCTION .................................................................................. 1
CHAPTER 2
MATERIALS AND SAMPLE CHARACTERIZATION ................................... 6
2.1 Materials .......................................................................................... 6
2.1.1 Epoxy Resins .......................................................................... 6
2.1.2 Curing Agents ........................................................................ 8
2.1.3 Promoter ............................................................................. 10
2.2 Sample Materials .............................................................................. 12
2.3 Sample Preparation ........................................................................... 17
CHAPTER 3

DYNAMIC MECHANICAL PROPERTIES OF EPOXY RESINS WITH

TRISILANOL PHENYL POSS ................................................................. 24
3.1 Dynamic Mechanical Analysis ............................................................ ”24
3.2 Results and Discussion ....................................................................... .27

3.2.1 DGEBA-Jeffamine p.230 cured at 100°C for 12 hours ..................... 27

 

CHA
YOU
4.1 ll
42 E
4.3 F
CH}
SUB

REI

3.2.2 DGEBA-DytecA cured at 100“c for 12 hours ............................... .31

3.2.3 NMR results of Amines with Trisilanol Phenyl POSS ..................... 35
3.2.4 TGDDM-Jeffamine D-230 cured at 150°C for 12 hours .................. .38
3.2.5 TGDDM-DytecA cured at 150°C for 12 hours ............................... 41
3.2.6 TGDDM-DytecA cured at 100°C for 24 hours ............................... 44
CHAPTER 4
FOURIER TRANSFORM INFRARED SPECTROSCOPY .............................. 47
4.1 Introduction .................................................................................... 47
4.2 Experimental Procedure ..................................................................... 47
4.3 Results and Discussion ........................................................................ 48
CHAPTER 5
SUMMARY ........................................................................................ .54
REFERENCES & NOTES ....................................................................... 56

vi

LIST OF TABLES

Table 2-1 Stoichiometric mixing ratios of DGEBA epoxy resin with Jeffamine D-230...19
Table 2-2 Stoichiometric mixing ratios of DGEBA epoxy resin with DytecA ............. 20
Table 2-3 Stoichiometric mixing ratios of TGDDM epoxy resin with Jeffamine D-230..21
Table 2-4 Stoichiometric mixing ratios of TGDDM epoxy resin with DytecA cured at
150°C for 12hours ........................................................................ 22

Table 2-5 Stoichiometric mixing ratios of TGDDM epoxy resin with DytecA cured at

100°C for 24hours ................................................................................... 23
Table 3-1 DMA results of DGEBA epoxy resin with Jeffamine D-230 ..................... 30
Table 3-2 DMA results of DGEBA epoxy resin with DytecA ................................ 34
Table 3-3 DMA results of TGDDM epoxy resin with Jeffamine D-23O .................... 40

Table 3-4 DMA results of TGDDM epoxy resin with DytecA cured at 150°C for 12
hours ...................................................................................... 43
Table 3-5 DMA results of TGDDM epoxy resin with DytecA cured at 100°C for 24

hours ...................................................................................... 46

vii

LIST OF FIGURES

Figure 1-1 Trisilanol Phenyl POSS ................................................................ 5
Figure 2-1 Diglycidyl ether of bisphenolA, DGEBA, (DER-332) ........................... 13
Figure 2-2 Tetraglycidyl diamino diphenyl methane, TGDDM .............................. 14
Figure 2-3 diamine terminated polypropylene oxide, Jeffamine D230 ...................... 15
Figure 2-4 2,Methyl 1,5 pentadiamine, DytecA ................................................ 16
Figure 3-1 DMA results of DGEBA epoxy resin with Jeffamine D—230 .................... 29
Figure 3-2 DMA results of DGEBA epoxy resin with DytecA ............................... 33
Figure 3-3 NMR Jeffamine- Trisilanol Phenyl POSS .......................................... 36
Figure 3-4 NMR DytecA - Trisilanol Phenyl POSS ........................................... 37
Figure 3-5 DMA results of TGDDM epoxy resin with Jeffamine D-230 ................... 39

Figure 3-6 DMA results of TGDDM epoxy resin with DytecA cured at 150°C for 12
hours ..................................................................................... 42
Figure 3-7 DMA results of TGDDM epoxy resin with DytecA cured at 100°C for 24
hours ..................................................................................... 45
Figure 4-1 FTIR results of DGEBA epoxy resin with DytecA ............................... 49
Figure 4-2 Epoxide consumption rate plotted against time for DGEBA-DytecA system.50

Figure 4-3 FTIR results of TGDDM epoxy resin with DytecA ............................... 53

viii

CHAPTER 1
INTRODUCTION

Epoxy resins are the most commonly used engineering therrnosets, in part due to
their excellent engineering performance upon curing and ease of processing prior to
curing. The broad interest in epoxy resins originates from the extremely wide variety of
chemical reactions and materials that can be used for the curing and the many different
properties that result. Depending on the chemical structure of the curing agent and the
curing conditions, it is possible to obtain mechanical properties ranging from extreme
ﬂexibility to high strength and hardness and high chemical resistance which can be used
to make therrnosets having high adhesive strength, good heat resistance and high
electrical resistance. Knowledge of the chemistry involved permits the user to cure over a
wide range of temperatures and to control the network structure that can lead to the
desired performance of the thermoset.

A signiﬁcant amount of work has been reported in the literature concerning the
nature of reaction between epoxides and aminesz. O’Neal and Cole concluded that the
only signiﬁcant reaction between an epoxy resin and an amine is that of the amino
hydrogens3. The reaction of epoxy compounds with amines is strongly inﬂuenced by the
nucleophilicity of the amine. A rapid increase in the rate of amine and epoxide
consumption can be induced by the catalytic effect of the hydroxyl groups generated‘.
The accelerating efﬁciency of the alcohol can be approximately proportional to its
acidity, which explains the high catalytic activity of phenols. This is because acids or
electrophilic species accelerates the addition of most nucleophiles considerably by the

reversible formation of the more reactive conjugated acid of the epoxide, as in the case of

Lewis acid like BF36’8. In addition to acceleration of amine- epoxides reactions via in-
situ-formed hydroxyl groups, the addition of compounds containing hydroxyl groups,
such as phenol, hydroxy alkylated polyamines, and adducts of oxirane or 1,2-
epoxypropane with polyamines, was reported to produce greater reactivity than that of
the parent arnineg. A particular problem exists with the use of phenol as an accelerator,

0, neurologically active11 and is

because it is highly corrosive to skin, co-carcinogenicl
coming under increasing regulatory pressure.

The development of additional cluster-based systems amenable to a broad range
of materials application has been of considerable intrest given the continuing demand for
new or retroﬁtted materials with enhanced properties. One class of compounds
potentially suited for such development is polyhedral oligomeric silsesquioxanes (POSS).
A surge of recent activity in this ﬁeld has been directed primarily towards the application
of POSS compounds in catalysis”.

Silsesquioxanes play an important role in the development of heterogeneous silica
supported transition metal supported catalyst systems. Octameric silsesquioxane resemble
skeletal frameworks found in crystalline forms of silica and zeolites, and their rigid
framework makes silsesquioxanes suitable models for silica surfaces. Of particular intrest
are the incompletely condensed silsesquioxanes which have one silicon removed from a

comer of the T3 cube. This T7 structure commonly referred to as a trisilanol, posses both

structural and electronic similarities to hydroxylated silica surface sitesg.

Polyhedral oligomeric silsesquioxane (POSS) are hybrid molecules of silicon and
oxygen with similarities to both silica and silicone. POSS are condensed silicon - oxygen

frameworks, which form random structures, ladder structures, cage structures and partial

cage structures when the silicon atom is attached with an organic group”. POSS
molecules with sizes of around lnm in diameter can be thought of as the smallest
particles of silica possible. POSS has a unique chemical composition, SiOLs, a hybrid
which is an intermediate composition between that of silica SiOz and silicone SiO. The
nature of the organic functional group determines compatibility with the polymer matrix.
The organic group can be a simple alkyl, cycloalkyl or aryl, or reactive/ polymerizable
groups such as acrylic, a-oleﬁn, styrene, epoxide, carboxylic acid, isocyanate, amine,
alcohol and silane, using such functionalization, the POSS structures can be either

copolymerized with a range of monomers, or grafted onto polymer chainsl‘Hs.

POSS molecules are physically of the same size with respect to polymer
dimensions and nearly equivalent in size to most polymer segments and coils. POSS
when mixed with virtually any ordinary polymer, bond to the organic molecules and to
one another, forming large chains that weave through the polymer. The POSS chains act
like nanoscale reinforcing ﬁbers, producing extraordinary gains in heat resistance.
Enhancements in the physical properties of polymers incorporating POSS segments result
from POSS’s ability to control the motions of the chains while still maintaining the
processability and mechanical properties of the base resin. This is a direct result of
POSS’s nanoscopic size and its relationship to polymer dimensions.

Incompletely condensed silicon-oxygen frameworks contain reactive silanol
functionalities. The reactivity of the silanol groups makes the POSS systems as models
for silica supported catalysis. In a typical comer capping reaction, when the trisilanol and
base are placed in a THF solution, slow addition of a trichlorosilane gave an excellent

yield of product. This was found to be true for isobutyl POSS trisilanol, but was not the

 

 

CBS

ﬁar

than

COTll

is k

TCEiC ‘.

inter

espet

case for phenyl POSS trisilanol. Instead of a single product, several compounds were
formed. The base used caused the problem by catalyzing the self-condensation of
trisilanol phenyl POSS'. This is because of the higher acidity of trisilanol phenyl POSS
than its aliphatic analogues'.

The basis of our work is to study what effect does stable non-toxic phenyl group
containing acidic systems have on the curing kinetics of the epoxy amine reaction since it
is known that acidic alcohol systems like phenol accelerate the epoxy amine curing
reaction. Recently with the availability of many nanoscale ﬁllers, we were particularly
interested in understanding the interaction between these ﬁllers with polymer chains,

especially phenyl acidic systems like trisilanol phenyl POSS.

Figure 1-1

Trisilanol Phenyl POSS

R = phenyl
C42 H380125i7 MW: 931.34 gr’mole
Soluble: letrahydrofuran, chloroform. ethanol
insoluble: hexane

- \ppcarancc: white powder

 

CHAPTER 2
MATERIALS AND SAMPLE CHARCTERIZATION

2.1 Materials

2.1.1 Epoxy Resins

Recent developments in polymer composite manufacturing have resulted in
higher quality and lower cost epoxy systems. Epoxies are thermosetting materials that are
used in a variety of applications including structural adhesives, coatings, and composites.
Epoxy resin is deﬁned as any compound containing two or more a- or 1,2- epoxy groups
capable of being converted to a thermoset form or a three dimensional network structure.
The curing of the epoxy resin is based on the reaction between the epoxide molecules
themselves or the reaction between the epoxy group and the other types of reactive
molecules with or without the presence of a catalyst. The former is referred to as
homopolymerization, and the latter is an addition reaction, but both result in coupling as
well as crosslinking. The curing process of a thermoset is governed by a competing
relationship between the diffusion controlled and concentration controlled reaction, when
the curing temperature is lower than the glass transition temperature the reaction is
diffusion controlled. When the curing temperature is higher than the glass transition
temperature, the reaction is concentration controlled. As the curing process proceeds, the
network structure improves thereby increasing the glass transition temperature.

Epoxy resins are used for transfer molding, compression molding, injection
molding, and reaction injection molding. The use of molded epoxy units has enjoyed a

wide acceptance in the electrical and electronic industries. The reasons for use of epoxy

molded compounds was because more reliable molding properties with a broader range
of flows are available from epoxy compounds including batch to batch reproducibility.
Also improved thermal shock resistance, permits the use of thinner wall sections, this
offers not only less material usage but also better component packing density. The
advantage of epoxy molding is the high production rates by virtue of short cycles, ease in
handling of resins and minimal amount of cleanup. Also the molded parts offer surface
ﬁnishes and overall appearance superior to most cast components. As compared to other
thermosetting compounds epoxy molding compounds are readily usable for long-ﬂow,
low - pressure molding operations, faster cure by addition reactions without evolution of
gaseous byproducts and a very low mold shrinkage, good adhesive bond to ﬁllers and
inserts, superior dimensional stability in the molded state, excellent electrical pr0perties
which are retained under high temperature and high humidity conditions and above all
epoxy molded systems have excellent resistance to most acids, bases, solvents, salts, and
other chemicals.

To reduce manufacturing costs many epoxy fiber composites are fabricated by
using resin transfer molding (RTM). Transfer molding is a process where a solid
material, in the form of powder or perform, is heated until it flows and is then transferred
into a mold cavity containing the unit to be molded.

The choice of curing agents is a critical factor in controlling properties; it not only
affects the properties of the cured resin, but also influences the rate of cure and the cure

exotherm.

F73.

2.1.2 Curing Agents

The term curing is used to describe the process by which one or more kinds of
reactants, i.e., and epoxide and curing agent, are transformed from low-molecular-weight
materials to a highly crosslinked network. Epoxy resin curing agents can be divided into
three technologically important classes: a) active hydrogen compounds, which cure by
polyaddition reactions; (b) ionic initiators, which are subdivided into anionic and
cationic; and (c) crosslinkers, which couple through the hydroxyl functionality of higher
molecular weight bisphenol A type epoxy resins. In order to achieve desired engineering
pr0perties various curing agents, which react with the epoxy rings to form insoluble and
intractable thermoset polymers, are used. For example, epoxy resins cured with anhydride
based curing agents exhibit low viscosity, low exothermic heats of reaction, and little
shrinkage when cured at elevated temperatures. The cured system exhibits good
mechanical and electrical properties along with good thermal stability that makes the
epoxy system useful in electrical applications.

Epoxy molecules linked together through the use of curing agents like amines,
anhydrides, anrides, etc form a three dimensional network. These network polymers at
temperatures below their glass transition temperatures are hard intractable solids, but are
rubbery above their glass transition temperature”. The characteristics of a network Epoxy
depend on the functionality of the resin, ﬂexibility of the epoxy chain, and the type and
concentration of the crosslinking agent.

Although, in a broad sense, epoxy-curing agents are classed as catalytic, most
cure by polyaddition reactions. Addition reaction is the most commonly used reaction for

the cure of epoxy amines. The most widely used curing agents, based on such active

 

hydrogen compounds as amines, acids, mercaptons, amides, and phenols undergo the
additions via the active hydrogen and the terminal carbon atom of the epoxy group, with
the subsequent conversion of the epoxy into a hydroxyl group.

These reactions are based on one active hydrogen in the curing agent per epoxy
group, practical systems are not always based on this stoichiometry because of
homopolymerization of epoxide or other side reactions, which may or may not be
avoided. A signiﬁcant amount of work has been reported in literature concerning the
nature of reaction between epoxides and amines. The reactivity of amine and modiﬁed
amines varies according to the steric hindrance in the neighborhood of the functional
groupss.

Several curing agents are used to cure epoxy resins out of which the most
commonly used are amines. Both aliphatic and aromatic amines are used to cure
epoxides. When aliphatic amines are blended with. a epoxy resin they yield a mixture
with a relatively short working life. They cure rapidly at room temperatures, and develop
very high exothermic temperatures during the curing process. Cracking or even charring
can result when a signiﬁcant amount of epoxy resin is mixed and cured at one time. The
physical and operating temperatures degrade rapidly as the operating temperatures
increases. Aliphatic amine cured epoxies ﬁnd their greatest use in small masses, where
room temperature curing is desirable and operating temperatures are below 100°C.

Aromatic amines cured epoxy systems have a considerably longer working life
than that of aliphatic amine systems. These systems are operated at much higher
temperatures and must be cured above 100°C. They are less easy to work with than other

curing agents because many are solids and must be melted into the epoxy. Some sublime

 

when heated causing strains and residue deposition. Further there are certain catalytic
cured epoxy systems which have longer working lives than the aliphatic amines but like
the aromatic amines they require cures of 100°C or higher. Piperidine, boron triﬂuoride-
ethylamine complex and benzyl dimethylamine are some of the catalytic curing agents
used to cure epoxy resins.

Liquid acid anhydrides are easy to work with, blend easily with the resins, and
reduce the viscosity of the resin. The working life of these systems is longer than that of
aliphatic amine cured systems. However many acid anhydrides are solids and are mixed
with epoxides at low temperatures giving pot lives as long as 10 days.

2.1.3 Promoter

The ring opening reactions of the epoxies takes place by ionic mechanisms. The
bond that is broken is the highly polar carbon-oxygen bond, which would be expected to
break ionically. The reactions are generally carried out in polar solvents, such as the
epoxy resin itself, and can be accelerated by adding polar agents. Under basic or neutral
conditions, all ring opening reactions are essentially similar and involve the attack of
nucleophile on one of the epoxide carbon atoms, as in the case of amine curing agent. A
difference exists when the reaction is carried out under acidic conditions. Acids or
electrophilic species because of the reversible formation of the more reactive conjugated
acid of the epoxide, as in the case of Lewis acid like BF3, accelerates the addition of
most nucleophiles considerably.

The effect of added compounds on the epoxy amine reaction decreases in the
order: acids > phenols > water > alcohols > nitriles > aromatic hydrocarbons like benzene

and toluene > dioxane > diidopropylether‘. The acceleration of the epoxide amine

10

 

reactions has been related to the ability of the accelerator to donate hydrogen bonds. The
list of hydrogen donors, and therefore accelerators, included -OH, -COOH, -SO3H, -
CONHz, -CONHR, -SOzNH2, and —SOZNHR. Conversely hydrogen bond acceptors like -
OR, -COOR, -SO3R, -CONR2, -CO, -CN, and —N02, retard the curing rate of the epoxy
amine reaction. Acids are not used to accelerate the epoxy amine curing reaction because

they form salts, but Lewis acids like BF3 do promote the epoxy amine reaction.

11

 

2.2 Sample Materials

The epoxy resins used in this study contained 0 to 1 wt% fractions of trisilanol
phenyl POSS. Two different conventional epoxy resins are used in this study. The ﬁrst
one is a diglycidyl ether of Bisphenol A, DGEBA (Dow Chemical DER 332), and the
second is tetraglycidyl diamino diphenyl methane, TGDDM (Aldrich Chemicals). Two
curing agents were used for each of the epoxy resins, one is a diamine terminated
polypropylene oxide; Jeffamine D230 (Huntsman Chemicals), and the other was
2,Methyl 1,5 pentadiamine; Dytec A (DuPont Chemicals). The chemical structures of the

components are described in Figure 2-1 through Figure 2—4.

12

 

MWEOYOM

Diglycidyl Ether of BisphenolA

l3

Fig 2-2

A; . A
«NHL?

Tetra Glycidyl Diamino lDiPhenyl Methane

l4

Fig 2-3

NH
O /i\r 2
2.6

Jeffamine D-230

15

Fig 2-4

HzN/\r\/\NH2

DytecA

l6

2.3 Sample Preparation

The epoxy resins used in this study contained 0 to 1 wt% fractions of trisilanol
phenyl POSS. Two different conventional epoxy resins are used in this study. The ﬁrst
one is a diglycidyl ether of Bisphenol A, DGEBA (Dow Chemical DER 332), and the
second is tetraglycidyl diamino diphenyl methane, TGDDM (Aldrich Chemicals). Two
curing agents were used for each of the epoxy resins, one is a diamine terminated
polypropylene oxide; Jeffamine D230 (Huntsman Chemicals), and the other was
2,Methyl 1,5 pentadiamine; Dytec A (DuPont Chemicals).

The DGEBA epoxide monomer was first preheated at 50°C for 30 minutes to melt
any crystals present. First, trisilanol phenyl POSS and DGEBA were mixed together and
stirred by hand. Then the equivalent of hydrogen of the curing agent (Jeffamine D230 or
Dytec A) is added to the equivalent of epoxy present and then the mixture is stirred by
mechanical means. The weights of each component in the sample mixture are tabulated in
Table 2-1 through Table 2-5. The mixture was then degassed in vacuum for 10 minutes at
room temperature. The mixture was poured in a mold and cured in an air oven at 100°C
for 12 hours, and then slowly cooled in the oven overnight to room temperature. Here the
oven was initially preheated to the curing temperature and then the mold was placed in
the air oven.

For the TGDDM the same process as above was adopted but the curing was done
at 150°C for 12 hours. The most important point in the preparation of the sample is that
the trisilanol phenyl POSS is ﬁrst added into the epoxy resin and later the curing agent

amine is added to the epoxy trisilanol phenyl POSS system.

17

The epoxy samples are cut into rectangular specimens and stored in a desiccator
at room temperature. These samples were used to perform Dynamic Mechanical Analysis

(DMA) experiments.

18

Table 2-1

DGEBA - Jeffamine D 230 cured at 100“C

 

 

 

 

 

 

 

 

 

 

 

Epoxy (g) Amine (g) POSS (g) %POSS
9.851 3.500 0.000 0.0
25.362 8.787 0.068 0.2
27.695 9.594 0.150 0.4
16.861 5.840 0.137 0.6
11.663 4.054 0.127 0.8
11.508 3.989 0.157 1.0

 

l9

 

DGEBA - DytecA system cured at 100°C

Table 2-2

 

 

 

 

 

 

 

 

Epoxy (Q Amine (g) POSS & %POSS
19.517 3.412 0.000 0.0
17.264 3.016 0.048 0.2
16.184 2.827 0.076 0.4
16.897 2.974 0.120 0.6
17.792 3.114 0.168 0.8
18.052 3.161 0.214 1.0

 

 

 

 

20

 

 

Table 2-3

TGDDM - Jeffamine D 230 cured at 150°C

 

 

 

 

 

 

 

 

 

 

 

Epoxy (g) Amine (g) POSS (i) %POSS
8.736 4.755 0.000 0.0
22.892 12.469 0.073 0.2
20.181 10.994 0.125 0.4
13.859 7.544 0.129 0.6
18.690 10.185 0.233 0.8
32.104 17.478 0.504 1.0

 

21

 

TGDDM-DytecA system cured at 1500C

Table 2-4

 

 

 

 

 

 

 

 

 

 

 

Epoxy (g) Amine (g) POSS (j) %POSS
16.738 4.595 0.000 0.0
17.275 4.743 0.044 0.2
14.342 3.938 0.073 0.4
17.748 4.873 0.136 0.6

' 17.230 4.730 0.177 0.8
15.450 4.242 0.199 1.0

 

22

 

 

Table 2.5

TGDDM-DytecA system cured at 100"C

 

 

 

 

 

Epoxy (g) Anrineig) POSS (g) %POSS
12.676 3.478 0.000 0.0
11.535 3.167 0.059 0.4
13.569 3.724 0.175 1

 

 

 

 

23

 

CHAPTER 3
MECHANICAL PROPERTIES OF EPOXY NETWORK GLASSES
CONTAINING TRISILANOL PHENYL POSS
3.1 Dynamic Mechanical Analysis

Dynamic Mechanical Analysis of polymeric solids is one of the most effective
and practical methods of studying the relationship between polymeric structure and
product performance. The viscoelastic measurements over the entire signiﬁcant
temperature range provide information on the usefulness of a material as determined by
the temperature dependence of its stiffness. From the corresponding mechanical loss data,
the internal transition behavior of the material can be studied.

Amorphous polymers are polymers having non-crystalline structure. Amorphous
polymers may have some molecular order but usually are substantially less ordered than
crystalline polymers and subsequently have inferior mechanical properties. Materials in
this class do not have detectable melting point. Glass transition temperature is the result
of the breakdown of amorphous region.

The Glass Temperature is deﬁned as the temperature range at which an
amorphous polymer (or the amorphous regions in a semi-crystalline polymer) changes
from a hard and relatively brittle condition to a viscous or rubbery condition. The glass
transition temperature is the temperature at which the material properties change from
those of a plastic to those of a rubber; this is a characteristic property of each substance.
The coefﬁcient of expansion of a substance undergoes a more abrupt change in the region
of glass transition. The temperature at this change is deﬁned as the glass transition

temperature. The temperature dependence upon cooling of the speciﬁc volume is

24

determined by a suitable technique and the temperature at the change in slope is taken as
the glass transition temperature T8. In this temperature region, many physical properties
such as hardness, brittleness, thermal expansion, and speciﬁc heat undergo rapid changes.
Coefﬁcient of Thermal Expansion (CTE) and Speciﬁc Heat of the polymer increases
when heated through the glass temperature Tg, but the Elastic Modulus decreases.

In Dynamic Mechanical Analysis the instrument applies a sinusoidal mechanical
strain deformation to the sample specimen. It measures four quantities: specimen
temperature, load (or stress), probe position (or strain), and time (or phase angle, 8).

The cured epoxy samples are cut into rectangular specimens for the DMA
experiments. The specimens are examined using a Rheometric Scientiﬁc Solids Analyzer
RSA III. The test samples have a span length of 25mm long. All the samples were
approximately of 12mm width and 2mm thickness. The sample dimensions are measured
and the specimen is loaded into the RSAIII. Three point bending supports a solid
rectangular sample in horizontal position. The sample ends rest on the motor, while the
transducer applies load to the center of the sample. The sample is bent around the fulcrum
held by the transducer where the transducer applies a small amount of static bending
force. The sample is therefore tested under a static bending mode. The sample is placed
on the lower tool ﬁxture of the three point beam and by adjusting the stage position to
bring the fulcrum to the sample, the fulcrum is allowed to touch the sample with
minimum amount of load, this provides a zero reference point throughout the test and
also ensure that the bearing overload warning is not displayed. The load of 100g was
initially applied on the sample at zero time and the test is started and the dynamic Elastic

(Storage) Modulus E’ and the tangent of the phase angle shift between stress and strain,

25

tan5 were determined. The test performed is a constant strain rate, constant frequency
temperature ramp test in three point bending mode. In all the cases a bending oscillation
of 27trad/s was used while heating at a temperature rate of 1°C/min for a strain rate of
0.02%. The measurements were carried out from room temperature to 100°C for all
DGEBA/Jeffamine D-23O samples and up to 150°C for DGEBA/DytecA and up to 250°C
for the TGDDM samples. The glass transition temperature is determined from the

tan8 curve. It is taken to be the temperature of the peak of the tan8 curve.

26

3.2 Results and Discussion

3.2.1 DGEBA-Jeffamine D 230 cured at 10000 for 12 hours

DMA curves of DGEBA epoxy resins having varying amounts of trisilanol
phenyl POSS and cured with Jeffamine D-230 are shown in Figure 3-1. This is nearly, a
completely cured system since the curing temperature is greater than the glass transition
temperature T > Tg, the curing reaction is concentration controlled for temperatures
below the Tg but it is diffusion controlled for temperatures above Tg. Figure 3-1 clearly
shows that the Glass Transition temperatures of the DGEBA/Jeffamine D-230/trisilanol

POSS samples are slightly higher than those of the neat DGEBA/Jeffamine D-230
sample. The glass transition temperature is determined from the tan8 curve. It is the
temperature of the peak of the tan5 curve. The T8 values of the DGEBA/Jeffamine D-230
samples with POSS composition varying by 0.2% from 0% to 1% are summarized in
Table 3-1. The increase of about 6°C is observed in samples containing trisilanol phenyl
POSS compared to the sample not containing POSS. This indicates that there is an
improved network formed in the case of samples containing POSS. Since the curing time
is only 12 hours, it can be said that the curing reaction is accelerated to form a better
networked system by trisilanol phenyl POSS in the case of samples containing POSS.
Dusek et al.17 found that the only reaction that occurred during the epoxy/amine reaction
when a phenol or an acid is present is the addition of the amino hydrogen to epoxy
groups. Oshiro, Komori, and coworkerslg'20 and Harrod2| reported that there is an
unequal activity between the amine functions and also reported that the primary amine
and the generated secondary amine had different reactivities toward the epoxy group“.

The presence of phenol in an acidic environment initially improves the rate of the

27

secondary amine reaction with the epoxy leading to an increased consumption of amine

and epoxy, thereby forming a better network.

To further investigate the effect of trisilanol phenyl POSS in epoxy amine systems
a more basic amine, DytecA than Jeffamine D 230 is chosen and DGEBA is cured with
DytecA. DytecA was used to study the effect of the basic amine curing agents on the

promotional activity of trisilanol phenyl POSS.

28

Figure 3-1 DMA results of DGEBA epoxy resin with Jeffamine D-230

 

 

 

 

 

 

 

: 1 ' I j l 1
d 2
1 09 1‘ t 10
I - 0.100 £30
10" “g ° DJ02 ”:2. 10‘
1 ‘ DJ04
Ta 1 v DJ06 _,
O.
V 107 ‘E O o g
in E 10 00
10°:
5 10“
1051
‘ 1 ' I ' I ' I . l ' I ' l r I ' I ' I 102

 

 

Temperature (°C)

D100 = DGEBA/Jeffamine D230/0% trisilanol phenyl POSS; D102 = DGEBA! Jeffamine D230 /0.2%
trisilanol phenyl POSS; D104 = DGEBA/ Jeffamine D230/0.4% trisilanol phenyl POSS; D106 = DGEBA]
Jeffamine D230 /0.6% trisilanol phenyl POSS; D108 = DGEBA/ Jeffamine D230 /0.8% trisilanol phenyl
POSS; D110 = DGEBA] Jeffamine D230 ll .0% trisilanol phenyl POSS

29

Table 3.1

Epoxy: DGEBA Amine: Jeffamine D-230

POSS: Trisilanol Phenyl-POSS

 

 

 

 

 

 

 

POSS wt% Tg DMTA (AT)*
0% 84.2(12)
0.20% 92.1(10)
0.40% 91.2(9)
0.60% 90.6(9)
0.80% 91.6(10)
1.00% 91.7(12)

 

 

 

 

0 Tg is determined by using tan§ curve, AT is the temperature range
at full width and at half height of the tan6 peak

30

3- 2.2 DGEBA - DytecA cured at 1 000 C for 12 hours

To study the effect of using a stronger basic amine on the curing reaction, DytecA
(pH=12.l) is used to cure the DGEBA epoxy resin containing varying amounts of
trisilanol phenyl POSS. The DMA curves for DGEBA epoxy trisilanol POSS with
DytecA as curing agent are shown in Figure 3-2. Here, there is an appreciable increase in
TE for samples with POSS compared to that of sample without POSS. The Tg values are
listed in Table 3-2. In the DytecA cured DGEBA epoxy systems, the low T8 of the neat
epoxy sample can be attributed to some unreacted functional groups that lower the
crosslinking density in the sample, but the point to be taken note of in here is that all the
samples with different POSS loading have nearly the same glass transition temperatures
T8. The near overlap of the DMA curves of 0.6% POSS and 0.8%POSS samples in
Figure 3-2 is a clear indication that the higher Tg has nothing to do with the POSS
grafting into the epoxy resin and also hydrogen bonding can be ruled out since the
observed Tg increase with and without POSS in the case of DGEBA and DytecA was
nearly 24°C for only 1.0% trisilanol phenyl POSS, which is not possible by pure
hydrogen bonding. Since the system is cured below its Tg, it is clear that the system
without trisilanol phenyl POSS is under cured and the curing reaction is diffusion
controlled. The higher Tg values of the epoxy samples containing trisilanol phenyl POSS
validate the point that trisilanol phenyl POSS promotes additional curing in the later

stages when the curing mechanism is diffusion controlled.

The Storage Modulus (E’) curves for the DGEBA-DytecA are shown in Figure 3.

The Storage Modulus (E’) in the rubbery region for the DGEBA-DytecA systems shows

31

 

I -._.-.,..—1-r

an increase for samples containing trisilanol phenyl POSS. Since the rubbery plateau
modulus is directly proportional to the crosslinking density. Increase in the modulus
indicates a higher degree of crosslink, which is the reason why trisilanol phenyl POSS
containing epoxy samples have a better Tg compared to neat epoxy samples. This shows
that trisilanol phenyl POSS promotes the curing reaction between the epoxy and the

amine.

A higher Tg value for DGEBA/trisilanol phenyl POSS system is observed with
DytecA compared to Jeffamine D-230 because DytecA (pH=12.1) is a stronger basic
amine than Jeffamine D-230 (pH=ll.7). NMR studies clearly show that DytecA is a

stronger amine than Jeffamine D 230.

To verify the above results with a different epoxy resin, a better cross-linking
epoxide having high temperature end applications was chosen. The epoxy resin used was
tetraglycidyl diphenyl diamino methane (TGDDM). Since TGDDM has four epoxy
groups compared to two for DGEBA and nearly the same middle chain, an improved
network is expected for TGDDM amine systems, so the Tg for the TGDDM amine
systems will be much higher than that of DGEBA amine systems. The TGDDM amine

systems are cured at a higher temperature than the DGEBA amine systems.

32

Figure 3-2 DMA results of DGEBA epoxy resin with DytecA

 

 

 

 

 

 

 

 

 

3 1 l T 1 I 1 1 1
109‘;
E 3 101
1081:
10"; - 10° 61
f a
10“;
f 1 10“
105';
10‘ I ' I ' l i 7 ' l f T ' r r 10.2
20 40 60 80 100 120 140 160

Temperature (°C)
DDOO = DGEBA/DytecA/0% trisilanol phenyl POSS; DD02 = DGEBA/DytecA /0.2% trisilanol phenyl
POSS; DD04 = DGEBA/DytecA [0.4% trisilanol phenyl POSS; DD06 = DGEBA/DytecA /0.6% trisilanol
phenyl POSS; DD08 = DGEBA/DytecA /0.8% trisilanol phenyl POSS; DD10 = DGEBA/DytecA / 1.0%
trisilanol phenyl POSS

33

Table 3.2

Epoxy: DGEBA Amine: DytecA

POSS: Trisilanol Phenyl-POSS

 

 

 

 

 

 

 

 

POSS wt% Tg DMTA (AT)*
0% 98.00(10)
0.20% 109.29(13)
0.40% 121.95(9)
0.60% 118.06(8)
0.80% 121.73(9)
1.00% 123.13(9)

 

 

 

o Tg is determined by using tanﬁ curve, AT is the temperature range
at full width and at half height of the tan5 peak

34

3.2.3 NMR Data of Trisilanol Phenyl POSS with Jeffamine D-230 and DytecA

The NMR plots of trisilanol phenyl POSS with Jeffamine D-230 and DytecA are
shown in Figures 3—3 and Figure 3-4 respectively. Dr. Haddad T.S. of Hybrid Plastics has
done the NMR experiments. The effect of Jeffamine D-230 on trisilanol phenyl POSS
can be clearly seen in Figure 3-3. At time t = lSminutes a decrease in the Phng peak is
observed which implies that the POSS cages are being descrambled but the effect is slow.
Since there is still a small peak it can be said that Jeffanrine D-230 will ﬁnally completely
descramble the POSS structure over time. After 75minutes a decrease in the phenyl triol

peak is observed with a crystalline substance forming on the NMR tube.

The effect of DytecA can be seen in Figure 34. After time t = 15 minutes we see
the POSS cages completely descramble, the phenyl trio] peak completely disappears.
This is possible due the high basicity of the amine used. From the NMR data it can be
said that the phenyl trio] (the acidic group which accelerates the epoxy/amine curing

reaction) lasts longer in the case of Jeffamine D-230 than in Dytec A.

From the NMR results we observe that the trisilanol phenyl POSS completely
descrambles the POSS cages in 15 minutes forming a rigid linear chain polymer. The
rigid polymer still contains the -OH groups, which are readily available for improving the

secondary amine reaction, which result in an improved network.

In the case of Jeffamine D230 the amine takes a longer time to descrambles the

POSS cages, which shows that DytecA is a stronger amine than Jeffamine D230.

35

Figure 3-3 NMR spectra of trisilanol phenyl POSS in Jeffamine D 230

 

 

 

 

O O \D
M m m
a: N N.
C) t‘ (D
‘0 F F
I I O
at time t = 0
"""" T"‘"""I"'"""I""""'l""'""1""""'I“"""'l"""'"I'T"'""1""""'l"'""‘"l‘
-69 -‘7-0 -'71 -'72 -'73 -'74 -75 -'76 -‘7'7

'69I098

.___...—. 43,122
*- ‘7‘ e 57‘

at timet= 15 minutes 1

 

.
'1
1" '
1'

 

 

‘ \ ~ ’ ‘ x. . ' ' ‘1. l V ‘ 1

r ,’ :1' ~l . -‘l' , g , .._ . ’ ‘1 ‘-i ,

WT ' ‘1"""“'IT"'V'T""I""' *"TI'W"""'I"""'T'TI'7" 7""~I""' " I" 'T""l“""""l""“"'l'
'69 -70 ~71 '72. -'73 -74 -"75 -'76 ' —'77

PF“

36

Figure 3-4 NMR spectra of trisilanol phenyl POSS in DytecA

 

at time t= Ominutes

 

 

 

l r r r T * ﬁ 1 r
80 60 40 20 0 -20 -40 -60 -80 -100 -120 ppm

at time t=15 minutes

 

I r r T a
-80 -100 -120 ppm

37

3.2.4 TGDDM-Jeffamine 0.230 cured at 150°Cfor 12 hours

Changing the epoxy resin to improved network forming epoxy resin like TGDDM
enhanced Tg improvement can be observed for TGDDM amine systems, as seen in Figure
3-5. The Tg values are listed in Table 3-3. The epoxy amine system is cured at a
temperature above its Tg so the epoxy network formed is nearly a complete cured system,
though an increase of about 12°C is observed for samples with trisilanol phenyl POSS,
this may only be to the less curing time employed for curing the epoxy systems where the
trisilanol phenyl POSS promoted the curing reactions when the curing reaction is
diffusion controlled for samples containing POSS thus leading to differences in glass
transition temperatures Tg between samples with and without trisilanol POSS. Also there
are no considerable differences in the Storage Modulus (E’) values for T < T3. The
difference between the epoxy systems cured with Jeffamine D-230 are that they are cured
at temperatures higher than their glass transition temperatures TE and the other systems
cured with DytecA have a much lower curing temperature much below their glass
transition temperatures T8. The increase of 12°C is justiﬁed because of the more rigid

TGDDM Jeffamine D230 system.

38

Figure 3-5 DMA results of TGDDM epoxy resin with Jeffamine D-230

 

 

 

 

 

 

d ' I r -1
9-
1° 5 1 10‘
108-: V K _ 0
To‘ 5 . TJ08 :10 _,
9.: I + 1.110 3 ‘3
[1.1 d I I. . O)
I. ' 6
O I "
107g ' °. .1
:1 o 0 -: 10
1061 ‘
. l r l I r I if U V 10.2

 

 

 

1 ' 1 ' 1 ' 1
20 4O 60 80 100 120 140 160 180

Temperature (°C)

T100 = TGDDM Ileffamine D230/0% trisilanol phenyl POSS; T102 = TGDDM / Jeffamine D230/0.2%
trisilanol phenyl POSS; T104 = TGDDM / Jeffamine D230/0.4% trisilanol phenyl POSS; T106 = TGDDM I
Jeffamine D230/0.6% trisilanol phenyl POSS; T108 = TGDDM / Jeffamine D230/0.8% trisilanol phenyl
POSS; T110 = TGDDM / Jeffamine D230/1.0% trisilanol phenyl POSS

39

Table 3.3

Epoxy: TGDDM
Amine: Jeffamine D-230

POSS: Trisilanol Phenyl POSS

 

 

 

 

 

 

 

 

 

 

POSS% TgDMTA (AT)*
0% 136.8(16)
0.20% 146.5(17)
0.40% 148.8(16)
0.60% 144.2(18)
0.80% 145.0(16)
1.00% 148.4(17)

 

o Tg is determined by using tanﬁ curve, AT is the temperature range
at full width and at half height of the tan5 peak

40

3.2.5 TGDDM-DytecA cured at 150°C for 12 hours

To observe notable changes in the glass transition temperatures the TGDDM
epoxy resin is cured with the more basic amine DytecA. The samples are under cured to
study the effect of trisilanol phenyl POSS on the curing kinetics of the TGDDM DytecA
system. The DMA curves are shown in Figure 3-6 and the glass transition temperatures
are tabulated in Table 3-4. As expected a notable increase in T13 of about 40°C is
observed. It is well known that epoxy resin shows a large tan8 peak in the glass transition
region. However the area of the tan6 peak decreased on the addition of trisilanol phenyl
POSS into the epoxy resin. This suggests that the trisilanol phenyl POSS is nearly
dispersed in the epoxy resin and motion of the network is strongly restricted by the
formation of a better network. From the NMR graphs it can be said that POSS
descrambles to form linear chain polymers. These polymers contain rigid —OH groups
that improve the secondary amine reaction rate thus improving the network formation by

the diffusion controlled mechanism of the curing reaction of TGDDM and DytecA.

Though initially the concentration controlled curing reaction occurs for low Tg
networks, that is when the mobility of the network is more, at a later stage the diffusion
controlled mechanism dominates the curing mechanism in network formation leading to
improved networks. An important point that was observed for the case of epoxy amine
systems containing POSS was that in parallel experiments conducted exactly at the same
experimental conditions showed consistent results which was not the case for epoxy
amine systems without trisilanol POSS. This was observed only for the epoxy amine

systems where the amine was DytecA.

41

Figure 3-6

DMA results of TGDDM epoxy resin with DytecA cured at 150°C for 12 hours

 

 

 

 

 

 

 

 

 

c1 —' 1 +
. ul
9-
10 E 3 10'
1 1
A - 04
E 10“ k E 10 g
:-’ 5 o TDOB : °°
Lu . .
. ' " 1. 10.1
1074. 3
1 4
1
I I l I l U l I I U I fl ﬁl’ I I V l I l I l U l' 10-2

 

1
0 20 40 60 80 100 120 140 160 180 200 220 240 260

Temperature (°C)

TDOO = TGDDM /DytecA/0% trisilanol phenyl POSS; TD02 = TGDDM /DytecA/0% trisilanol phenyl
POSS; TD04 = TGDDM /DytecA/0% trisilanol phenyl POSS; TD08 = TGDDM /DytecA/0% trisilanol
phenyl POSS

42

Table 3.4

Epoxy: TGDDM Amine: DytecA

POSS: Trisilanol Phenyl-POSS

 

 

 

 

 

 

 

POSS wt% Tg DMTA (AT)*
0% 166.99(25)
0.20% 214.11(16)
0.40% 220.29(20)
0.60% 219.18(19)
0.80% 192.93(28)
1.00% 212.81(15)

 

 

 

 

- Tg is determined by using tan§ curve, AT is the temperature range
at full width and at half height of the tan8 peak

43

3.2.6 TGDDM-DytecA cured at 100°C for 24 hours

Now we made another set of samples of TGDDM using DytecA as curing agent
and cured them at 100°C for 24 hours. DMA analysis on these samples is shown in
Figure 3-7. The glass transition temperatures Tg observed are tabulated in Table 1. We
observe a small peak at nearly 135°C in the tanﬁ curve for the DMA curves, this shows an
additional cure taking place, which is possible since the heating rate is only 1°C/minute
and the curing temperature for the samples was far less than the glass transition
temperature T3. The glass transition temperature T8 of the neat TGDDM/DytecA
decreased when compared to the glass transition temperature Tg of neat TGDDM/DytecA
cured at 150°C for 12 hours, this clearly shows that the system is uncured, but the
TGDDM/DytecA containing trisilanol phenyl POSS (1.0%) showed the same results in
both the cases. This indicates that POSS has accelerated the curing reaction in the case of
the POSS containing epoxy amine samples and a much lower temperature is required for

the curing of the epoxy resin using an amine.

The above DMA results shows that the presence of a small amount of POSS could
signiﬁcantly increase the T8 of neat epoxy resin at low curing temperatures, because the
addition of 0.2% is not likely to increase the viscosity of the epoxy resins, it is thus of

importance to the POSS application in low temperature curing process.

 

Figure 3-5

DMA results of TGDDM epoxy resin with DytecA cured at 100°C for 24 hours

 

  

 

 
  
  

 

 

 

 

 

 

o 1 r 1 1 T 1 1 1 10
10’:
Z TDDO_IC a
- 1 10
q 0 TDD4_IC :
e TD10 It: I
A ' _ . 51
U 4 D
e“ 10' 1 0'
EU 3
j 1 10'1
. 1
1
.1 '1
107 1
: 1
‘ . , . , . , . , . r 10"
0 50 100 150 200 250
Temperature C C)

TD00_1c = TGDDM [DytecA/0% trisilanol phenyl POSS at low temperature cure; TD04_lc = TGDDM
/DytecA/0.4% trisilanol phenyl POSS at low temperature cure; TD10_lc = TGDDM [DytecA/1.0%

trisilanol phenyl POSS at low temperature cure.

45

Table 3.5

Epoxy: TGDDM Amine: DytecA

POSS: Trisilanol Phenyl-POSS

 

 

 

 

POSS wt% Tg DMTA (AT)*
0% 198.17(20)
0.40% 210.07(21)
1.00% 222.70(16)

 

 

 

 

o Tg is determined by using tan§ curve, AT is the temperature range
at full width and at half height of the tan8 peak

46

CHAPTER 4

F OURIER TRANSFORM INFRARED SPECTROSCOPY

4.1 Introduction

Fourier Transform Infrared Spectroscopy is an important technique to identify the
presence of certain functional groups in a molecule. Fourier Transform Infrared
Spectroscopy (FTIR) measures dominantly vibrations of functional groups and highly
polar bonds. FTIR spectrometers record the interaction of infrared (IR) radiation with
experimental samples, measuring the frequencies at which the sample absorbs the
radiation and the intensities of the absorptions. Since chemical functional groups are
known to absorb light at speciﬁc frequencies, determining these frequencies allows
identiﬁcation of the sample's chemical makeup. FTIR experiments generally can be
classiﬁed into two categories; one is qualitative analysis where the aim is to identify the
sample and the other is quantitative analysis of the intensity of an absorption (or more

commonly absorptions), which is directly related to the concentration of the component

4.2 Experimental Procedure

Fourier transform infrared spectroscopy (FT IR) was used to monitor the curing
kinetics of epoxy resins. In each experiment, samples were cast into thin ﬁlms on FTIR
cards (polyethylene) after immediately mixing the equivalent weights of epoxide and
amine. These FT IR cards were placed in an oven at desired temperatures, and they were
subjected to FTIR scans periodically during the experiments. FTIR spectra were

obtained using a Bio-Rad FT S3000. Each spectrum represents the average of 68 scans.

47

4.3 Results and Discussion

FTIR was used to study the curing kinetics of two systems: DGEBA with DytecA,
and TGDDM with DytecA. Figure 4-1 shows the FTIR spectra of sample
DGEBA/DYTECA/0.4%POSS cured at 60°C. The detailed peak assignment can be
found in the literature [ref]. In this study, we used the aromatic C=C stretching peak
(1510 cm") as an internal standard. We note that because the POSS molar ratio was very
small in the sample DGEBA/DYTECA/0.4% POSS, the contribution of the phenyl
groups in the POSS is negligible due to the high molecular weight of trisilanol phenyl
POSS. The peak at 914 cm'1 was used to calculate the consumption rate of epoxide. As
seen, the peak intensity of epoxide obviously decreased in the curing process. However,
there was still a signiﬁcant epoxide peak even after 1020 min. This is because the chosen
curing temperature in this experiment was much lower than the Tg (typically at 90°C) of
the epoxy resin. Therefore, the conversion of epoxide is lower. The etheriﬁcation peak
(1070 cm") was found to be insigniﬁcant in both DGEBA/DYTECA/0%POSS and
DGEBA/DYTECA/O.4%POSS samples. Thus, the presence of POSS did not promote
the etheriﬁcation of DGEBA, and the etheriﬁcation effect can be neglected in this study.
Hydroxyl group at 3450 crn'I was observed in both DGEBA/DYTECA/0%POSS and
DGEBA/DYTECA/O.4%POSS samples. Since the contribution of silanol group is low
because of its low molar ratio, the hydroxyl peak should be due to the backbone of the
epoxy resin that contains the hydroxyl group. The intensity of hydroxyl group showed
barely observable increase in sample DGEBA/DYTECA/O.4%POSS despite the fact that

it showed signiﬁcant Tg improvement than sample DGEBA/DYTECA/0%POSS. It is

48

Intensity (arb. unit)

Figure 4-1 FTIR results of DGEBA epoxy resin with DytecA

Aromatic C=C stretching

   
  
 

' Hydroxyl / Epoxide
1 'Al ° 1
l, ‘1 ,1 1020 min
_.____ _ -2 AU! V\w-xw./A°I V‘ ‘WM/LM
. 480 min
i 240 min

. .JI‘ ’f-V‘RH ﬂ ’,’ 1‘ 120 min
. . vg/ - J; x 4}, \ ... \\

1......HH. q W’Jingfk ,_-. I; i g _ 7‘ . .1 . ~../\, L] V"W
. JAM/’NJAMW

W

 

 

 

I ' Jill I I ' I I V I l ﬂ
3500 1 750 1 500 1 250 1 000 750 500

Wavenumber (cm")

49

Figure 4-2 Epoxide consumption rate plotted against time for DGEBA-DytecA

 

 

 

 

 

 

system

0.6-

0.5- o 0004 (0.4% POSS)
:3 J o DDOO
(D
:9 0.4-4
X
o .
Q.
3 0.3-
0 O
c .
.9 , ' a
g 0.2- . g D

O. D
E!
. I 0 °
D

o 01— 3‘9

0.0 ’7 I l I ' I I I I I l l I

0 200 400 600 800 1000 1200
Time (min)

DDOO= DGEBA I DytecA/0%trisilanol phenyl POSS; DD04= DGEBA/ DytecA / 0.4% trisilanol phenyl
P088

50

known that the curing kinetics can be accelerated by strong acidic catalysts, such as BF3,
phenolic acid. Even though the acidity of trisilanol phenyl POSS could be close or
superior to phenolic acid, the presence of POSS in the epoxy resin, however, did not
revoke catalyzed reaction. To further quantitatively investigate this result, the conversion
rate of epoxide was presented in Figure 4-2. The conversion of epoxide was calculated
using the area of epoxide (914 cm") at different curing time divided by the area of
epoxide immediately after mixing the DGEBA and DytecA. As seen, the conversion of
epoxide showed rapid increase in the ﬁrst 15 mins. After that, the conversion of epoxide
followed a decreased increasing rate. After 1020 min, the total conversion of epoxide
was 28% in sample DGEBA/DYTECA/O% POSS and 22% in sample
DGEBA/DYTECA/O.4% POSS. This conversion value is considerably low due to two
facts: the curing temperature was 30°C lower than the Tg of the ﬁnal product, and the
DytecA actively reacted with DGEBA at room temperature initially during the process of
mixing. Nevertheless, the calculation shows that the conversion of epoxide was lower for
DGEBA/DYTECA/O.4% POSS in the total time frame, which supported our argument
that the trisilanol phenyl POSS was not catalyzing the curing of epoxy resin. In a
separate measurement, the conversion rate of epoxide showed no difference in
DGEBA/DYTECA/0% POSS and DGEBA/DYTECA/0.4% POSS cured at 100°C (about
10°C higher than the Tg of the ﬁnal product). Thus the slightly lower conversion rate in
DGEBA/DYTECA/O.4% POSS is attributed to the increasing chain entanglements in the
presence of POSS molecules at temperatures lower than Tg, where the epoxy network has

much less mobility. This observation was in contrast to the ﬁlled silica system, where the

51

curing kinetics was accelerated by a hypothesized free volume effect22'23. The researchers
hypothesized that the presence of ﬁlled silica decreased the free volume of the system
and thus increased the local concentration of epoxy monomers. In the epoxy-POSS
system, however, we believe that the presence of nanosized POSS molecules did not
signiﬁcantly decrease the free volume. Furthermore, because the POSS molecules were
much smaller than the conventional silica when dispersed at the molecular level, the
interface between monomers and the POSS (the place where the catalysis effect is
believed to take place) should be small. Thus, the ﬁller effect, which hypothesized to
cause high concentration of monomers at local area, should be minimum in this study.
The FTIR results on TGDDM based epoxy resin further supported the above
argument. Two samples were subjected to the FTIR analysis:
TGDDM/DYTECA/0%POSS and TGDDM/DYTECA/0.4%POSS. The curing
temperature was 100°C (approximately 100°C lower than Tg) and 150°C. Figure 4-3
shows the FI‘ IR results of these two samples after curing for 900 min at 100°C. As seen,
there is no signiﬁcant difference between these two samples. Quantitative calculation
shows that sample TGDDM/DYTECA/0.4% POSS shows barely observable increase in
hydroxyl peak at 3450 cm". Similar observations were also found in samples cured at

150°C for 900 min.

52

 

Figure 4-1 FI‘IR results of TGDDM epoxy resin with DytecA

 

 

 

 

 

_J
.4
A J
E - TDO4(0.4% P088)
3 -1
e’ 1
3 JW w
g _
w -
c
513 -
E .1
d T000
.1
W
.11
l ' Ill ' l ' l ' l ' l ' l
3500 1750 1500 1250 1000 750 500

Wavenumber (cm'1)

TDOO= TGDDM / DytecA / 0% trisilanol phenyl POSS; TD04 = TGDDM / DytecA / 0.4% trisilanol
phenyl POSS

53

CHAPTER 5

SUNIMARY

The Glass transition temperature from the tan5 peak is used to characterize the
cure state and its development during cure of an epoxy resin using trisilanol phenyl POSS
as a promoter in the curing reaction. It is seen that there are signiﬁcant increases in the
glass transition temperatures for systems that are cured much below their glass transition

temperatures.

Normally epoxides are cured with amines to improve speciﬁc properties or
applications such as pot life, flexibility, speed of cure, lower toxicity, and lower exotherm
in large castings. Though epoxies cured with aromatic amines form better cross linked
systems than the aliphatic systems they require elevated temperatures to cure, also %

amine reacted is very less compared to that of aliphatic amines.

In this study, we demonstrated that the addition of small quantities of trisilanol
phenyl silsesquioxane (trisilanol phenyl POSS) molecules could induce a promoted
network in epoxy resins. Dynamic Measurement Analysis (DMA) results showed that the
trisilanol phenyl POSS containing POSS had a uniformly higher Tg than the neat epoxy
amine system, only 0.2% trisilanol phenyl POSS showed a marked improvement in the
glass transition temperature compared to the neat epoxy amine system and also this
promotion of Tg was found to be independent of the POSS concentration. This suggests

that the ﬁller effects did not cause the increase in Tg. The increase in Tg was due to the

54

 

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acid catalyzed reaction by the acidic phenyl silanol groups present in the Silsesquioxane

(trisilanol phenyl POSS).

It was postulated that phenyl silanols promoted the reaction of the secondary
amine to form an improved network, since the later stage of the curing process between
epoxy and amine is diffusion controlled, the size of POSS and the acidity of the phenyl
trisilanol were the two main reasons for the epoxy amine system to form an improved
network connectivity, even though the total mobility of the epoxy network might be
retarded somewhat because of the presence of POSS molecules, the diffusion-controlled
secondary amine reaction can still gain better local mobility around the POSS molecules
to form a more balanced network. This observation is considered to have industry uses
for ensuring better end use properties of the epoxy aliphatic amine systems at much lower

temperature cures than their glass transition temperatures.

55

8.

9.

REFERENCES & NOTES

. The pKa of the cyclopentyl POSS trisilanol is reported to be 7.6. R. Duchateau, U.

Cremer, R. J. Harrnsen, S. I. Mohamud, H.C.L. Abbenhuis, R.A. van Santen, A.
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Organometallics 18,5447 (1999).

May, Clayton A. Epoxy resins: chemistry and technology, New York: M. Dekker,
(1988)

O’Neil, LA. and Cole C.P., J. Appl. Chem., 6:356 (1956)

Smith, I.T. Polymer 2:95 (1961)

Ingberman, AK. and Walton, R.K. J .Polymer Sci, 28:468(l958)

Allen, R]. and Hunter, W. M., J. Appl. Chem., 7286(1957)

. Goh, Y.; Iijima, T.; Tomoi, M, J. Polym. Sci., Polym. Chem, 40,2689 (2002)

Kim, W. G.; Yoon, H. G.; Lee, J. Y., J. Appl. Polym. Sci., 81,2711 (2001)

Baney, R.H., Itoh, M., Sakakibara A., and Suzuki, T. Chem. Rev. 95,1409(1995)

10. Lamela, C. P. et al., Analusis, 21(9), 367 (1993)

ll.

12.

13.

14.

15.

16.

Henry Lee; Kris Neville, Epoxy Resins: their application and technology,
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Lichtenhan, Joseph, D. Comments Inorg. Chem., 17(2), 115-130 (1995)

Feher, F. J. et al., Organometallics, 10,2526 (1991)

Feher, F. J. et al., J. Am. Chem. Soc., 116, 2145 (1994)

Feher, F. J. et al., J. Am. Chem. Soc., 113, 3618 (1991)

Miller, M. L., The Structure of Polymers, Reinhold Book Corporation, New York

(1966)

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17. a) T. Kakurai and T. Noguchi, J. Soc. Org. Syn. Chem. Jpn., 18, 485 (1960).
17.b) T. Kakurai and T. Noguchi, Kogyo Kagaku Zasshi, 63, 294 (1960)‘
17.c) T. Kakurai and T. Noguchi, Kogyo Kagaku Zasshi, 64, 398 (1961)‘
17.d) T. Kakurai and T. Noguchi, Kogyo Kagaku Zasshi, 65, 827 (1962):.

18. S. Komori and T. Karaki, Kogyo Kagaku Zasshi, 62, 538 (1959f

19. Y. Oshiro, T. Tsunoda, and S. Komori, Kogyo Kagaku Zasshi, 64, 2132 (1961).
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21. J. F. Harrod, J. Polymer Sci., 1A, 385 (1963)

22. Paz-Abuin et al., J. Polym. Sci. Part A, 36, 1001 (1997)

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(2001)

‘ The references cited were not read but the content of which was translated and was
referred by May, Clayton A. Epoxy resins: chemistry and technology, New York: M.

Dekker, (1988)

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