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The POLYMERIZATION of EPOXIDES
By MEANS of the GRIGNARD
DERIVATIVES of t-BUTYL BROMIDE

THESIS for the DEGREE of M. S.
MICHIGAN STATE COLLEGE

John Roscoe Peffer
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JSIGSB

AC “(VIEW

Th0 author wiahaa to express Ml gratitude and :pprocintion for
the help and enema-«gamut. given by Dr. Ralph L. 62111. and Dom Entru-
1tus Pulp}: C. Huston during tho courso of this investigstion.

DEDICATION

To 11w wife

ABSTRACT OF THESIS,

by
JOHN R. porn-rs

Title: The Polymerization of Epoxides by Means of the Grignard Deriva-

tives of t-Butyl Bromide.

Tertiary butylmagnesium bromide, anhydrous magnesium bromide,
and di-tertiary butylmagnesium were investigated as possible catalysts
for the polymerization of ethylene oxide, propylene oxide, butadiene
monoxide, and ‘styrene oxide.

The monomer and catalyst were combined and shaken in a closed
system. The polymers were purified by dissolving them in chloroform
and removing inorganic material by centrifugation. The high and low
molecular weight fractions were separated by precipitating the high
molecular weight material with diethyl ether from.a chloroform solu-
tion. The intrinsic viscosities of the various polymers were deter-
‘nhedd. The optimum catalyst concentrations were determined and the
effect of removing the catalyst solvent was studied.

Tertiary butylmognesium bromide resulted in high yields of low
molecular weight polymers of ethylene oxide. The proportion of high
molecular weight polymer to low molecular weight polymer increased with
decreasing catalyst concentration. An anionic mechanism of polymeri-
zation was presented. Poorer yields of polymers were obtained from
the other monomers when t-butylmagnesium bromide was used as the cat-

alyet.

Magnesium bromide caused fair yields of ether soluble, low mole-
cular weight polymers from all the epoxides used. A cationic mechanism
of polymerization was suggested.

Di-tertiary butylmagneeimn was a good catalyst for the production
of high molecular weight polymers of ethylene oxide. At the concentre-
'tione used, it was ineffective against propylene oxide and butadiene
monoxide, and caused a poor yield of low molecular weight polystyrene

oxide. A free radical mechanism wee proposed.

TABLE OF CONTENTS

3’
“3

Introduction-a-o------u---—-----------
Historical------------------------—--
Experimentaln-o---—-------------..----..
Preparation of Catalyst Solutions--.- --.. - - -- - a... .-
1. Preparation of t—hutylmngnesium bromide- --- .. q. ..

2. Preparation of anhydrous magnesium bromide etherate- -

3. Preparation of di-tobutylmagnesiuu eolution- «- - - - «-

GOQQQONP

Polymerizatione-~-ga-ug-g-ao—uua-----a-
1. The reactions of epoxides with low concentrations of
t-butylmamesiumbromide----«--—-u------- 8
2. The rmctions of epoxides with anhydrous magnesium
bromide etherate'---- nan----------.---10
3. The reactions of epoxides with varying concentrations
of dict-butylmsgmssium------------§-----m

Purification ofPolymers -..----------------11

Determination of Intrinsic Viscosity and ".olecular Weight - - 11

Tables “Experimental Results ------------- --—-13
Results-uo------ --——--------------- 23
Discussion-~---------~----..-..-....----- 26

1. Optimum conditions for polymerization - <- - - - - - - - - 26

2. Possible mechanisms of polymerization - - - - - - - - - - 29

SW17..-—o-I-bee-u—I-d-a-o-canon-oquaouo- 3’

Francis Erma. a graduate studmt in this laboratery, carried
out a reaction between two moles of premium exide and one mole e!
diptgbutylmagnesiun. He did not obtain the expected addition predict
which would Ivdrelyee te' give b.h.~dimthylp2opmtane1. Instead , be
separated a white gumy mass which was insoluble in ether . melted ever
a wide range and could net be distilled. '

This phenomenon prompted this investigation to determine the ep-
timum conditions for the polymerization at some epexides with t-butyla-
magnesium bromide and its equilibrium products , di-t-butyluglesiun and

magnesium bromide.

HISTORICAL

The polymerization of ethylene oxide, the simplest epoxide, was
accomplished and studied by Staudinger in 1928. (1) He proposed the
polymer molecule to be a linear chain with ether linkages between the
individual units. Practically the same products were obtained with
basic catalysts, (tertiary amines, alkali metals, etc.) and acid cat-
alysts, (e.g. stannic chloride). The polymers were not homogeneous
but were a mixture of various molecular weight homologs. By fraction-
al precipitation the mixture was separated into polymers varying in
molecular weight from.h50 (a viscous liquid) to h500 (a waxy solid).
The polymers were rather stable; they decomposed only above 300’ C.
They were very readily soluble in organic solvents (except petroleum
ether and diethyl ether) and water.

Soon after Standinger's publication, a series of patents (2) (3)
(h) (S) (6) (7) appeared on methods of polymerizing ethylene oxide.
Without exception, these patents involved the use of potassium hydr-
oxide or sodium hydroxide as catalysts. Witwer'a patent (5) also takes
advantage of the fact that if the solvent is a low polymer of the
monomer, (e.g. diethylene glycol) further polymerization will occur to
give a homogeneous product. In the United States, Carbide and Carbon
Chemicals Incorporated manufactured and distributed;polyethylene oxides
under the trade name "Carbowax". ("Oxydwachs", German). The two
principal forms are Carbowax 1000 and Carbowax 4000 ( the number indi-
cates average molecular weight) which are used in large tonnapes in

detergents, pharmaceuticals, and cosmetics. (8)

3.

During his studies with ethylene oxide, Standinger also investi-
gated the polymerization of propylene oxide. (9) Propylene oxide
polymerized under the influence of anhydrous stmnic chloride with
extraordinary violence. For the most part, it formed low-molecular weight
polymers which were generally liquid. By fractionating, it was poe-
sible to separate a high molecular weight product which was send-solid.
This semi-solid product melted only at a high temperature and was easily
soluble in bensene.

Butadiene nonmdde, 3,5-epozqr-lpbutem is an interesting monomer
since it contains two different polymerizsble groups. Thus three types
of polymerization are possible; (q) exclusively through the double
bond, (b) exclusively through the We head, or,_(c) a combination of

the previously suggested means.

 

 

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m (6)

However, Bleor, in this laboratory (10) showed that butadiene mon-
adds was polymerizable only under conditions much more rigorous than

its pseudo-dielefin characteristics would imply. He found that mass

polymerisation with sodium hydroxide resulted in a polymer high in
double bond content and that a sodium sand catalyst caused the formation
of a polymer high in epoxide content and relatively low in unsaturation.
Bensoyl peroxide, sodium formaldehyde sulfoxylate, tubutyl peroxide and
sine chloride were ineffective as catalysts while concentrated sulfuric
acid caused violent polymerization and decomposition. The polymers ob-
tained were soluble in ethyl alcohol, methyl alcohol and acetone and in-
soluble in ether, benzene and carbon tetrachloride.

The use of styrene oxide, 1,2-epoxyethyl benzene, as a polymeriza-
ble monomer has not been studied,

The reactions between organs-magnesium comeounds and epoxides have
been investigated extensively, ‘

The investigators have shown that ethylene oxide and Grignard reagents
resulted in primary alcohdls. (11) (12) Substituted epoxides reacted
with organs-magnesium halides to give secondary alcohols upon hydrolysis.
(11) The exception was styrene oxide which gave primary or secondary al-
cohols depending upon the order of addition. (1h)

Stevens and HoCoubrey'(15) and Huston and Branlt (16) noted that
t—butylmagnesium'bromide when reacted with an epoxide gave a very poor
yield of the alcohol. Huston and Erault obtained a fair'yield of the
bromohydrin of the epoxide and a triner of the epoxide. They also ob-
tained the bromehydrin by reacting the eooxide with anhydrous magnesium
bromide in dry ether and hydrolyzing the precipitate.

In the reaction between epoxides and dialkylmsgnesium.compounds

many workers have obtained gummy and resinous bybproducts. (17) Barb-

lett and Berry (18) reacted two-tenths of a mole of cyclohexsne oxide

5.

with an equivalent amount of diethylncgncsiuu and obtained five and
one-half grams of polymer representing twenty-two percent of the start-
ing materials. Goltmbio and Cattle (19) obtained 24henyl-l-propanol

and polymer when they hydrolyzed the reaction mixture of styrene oxide

and dimethylmagnosium. Huston and Tiefenthal (20) also isolated a
polymeric nose when they permitted propylene oxide and di~t~bdtylmagnesium
to react for a considerable length of time. .

Grignsrd reagents have been investigated as catalysts for the poly»
merizstion of monomers by Beacon (21), Landler (22), and Reedel (23).

Bruylont and coworkers (21;) (25) obtained large amts of diners
and trimers when they carried out a reaction between organs-magnesium
bromides and allyl cyanide. ‘

Bones (2].) polymerized methacrylonitrile by scans of butylaoglesius
bromide, phenylmagncsium‘bronide, triphenylnethyl sedium and sodium in
liquid amonia. He obtained, from use of the Grimerd reagent, a light
yellow solid polymer with a molecular weight estimated at 8000.

Ladler (22) pelymerised uthyl nethecrylate with butylmgnesitm
bromide containing radioactive bromine. He showed that m catalyst
initiated polymerisation by direct action on the noncom- and that ter-

. mination occurred without catalyst dissociation. Both Beam and Lsndler
proposed ionic mechanisms for the polymerizations.

Reedel (23) achieved ethylene polymersd high molecular weight and
high tensile strmgth by reacting ethylene with 0.005 ~ 51 of ergono-
metallic halides in an inert solvent such as bmcccc at 100' 0. to 250° c.

and at ethylene pressures of A00 - 1500 atmospheres.

RIVERIMHITAL

21mm.

1. Ethylene undo, b.p. 12° c./‘w.o m., obtoiuod 1:: cylinders from an
Rathooou Company.

2. Propylono oxide, 13.9. 33.1; .- 31..” C./‘7£.O 3.. Dow Chlmiool Company.
3. LHW-L-Mmg Columbio annual. Division of The Pittsburgh
Put. em: Company; magnum—.mp. 65 - 67" mm» In.

a. Styx-mo amide, Dow Chemical am (reamed); ”manner-mp.
so - 61° c./a an.

event 8
1. rerun-y M11 bromido, Enatm Rodd! Company.

2. Hagnosim turning: for (Edward reactions, Dav Chou-tool Company.
3. Anhydrous didhhyl othor, OJ. driod over sodium who for st loan
on. weak.
I». Bromine. Kaboom Chm”). Compuv.

5. Lip-Dianna. Eastman 'Proctiool' m purifiod by tho ”thud of
Flour (26). It was kept no» nitrogen-ma .ovor sodium.
6.. Silver unto“, Hannah-ooh Ola-mica}. coupon. Abolition Rupnt.
7. Sodium thiocymto, Hollinokrod‘h Chi-10a]. company. 0.9.

8. Nitrobonom, Eastman Kodak Gunpony.
9. Standard hydrochloric acid solution. 0.1781 H.
10. Standard «dim ”druid. solution. 0.0986 R.

7.

3mm .9; W W!
1. Preparation of t-butylmgnesium bromide.

‘ Thirty g. of clean dry magnesium.turningo and 100 ml. of dry di-
ethyl ether were pleced in e dry, one liter round-bottom flask equipped
with e reflux condenser, nitrogen addition tube, dropping funnel, end e
mercury-aeoled stirrer. The opporetus was swept with nitrogen, and while
oooling in en ice bath, one mole (137 g.) of tnbutyl bromide on two-hundred
ml. of dry diethyl other were poured into the dropping funnel. About five
ml. of the mixture was added to the magnesium and other in the flank end
stirring was started. The reaction initiated very easily; After'it had
etertedthe bromide solution we added very slowly over e period of two
end one-hell to three hours. The mixture was etirred in the cold for two
more hour: and then allowed to stand overnight.

The black solution mi forced bynitrogen preeeure through a tube with
e glue wool plug into e nitrogen-filled bottle “eh wee then tightly
etonpered. The reagent was titrated with otendnrd ecid_hy Gilmonfie‘nethod.
(27) on. concentration woe generally 1.2 - 1.6 u. representing e 1.0 - 50%
yield. .

2. Prepmtien of enhydroua mmeeiun bromide etherate.

Twenty-nix ml. (80 g.) of bromine was added ever 3 period of two
hours to 15.5 g. of magnuium turning: in 250 ml. of dry other. The mix-
ture was kept under nitrogen. cooled in on ice-bath, end was well etirred.
'flle- bromine was edded et suoh e rete on to pernit gentle reflux. After
addition was complete, tho mixture was left standing overnight. i two
leyer eyetem formed, the lower, darker one containing the bulk of the

.8.

neglesium bromide. There was also a small emount of solid precipitate.
The solution was removed from the excess magnesium by forcing the liquid
through I glass wool plug in a delivery tube by applying nitrogen pressure.
The concentration of the HgBrz in the lower layer was found by determining
the bromide ion concentration by mans of the‘Volhard procedure. (28) The

concentration of this lower pheae was found to be 2.5 M.

3. Preparation of di-tobutylrdegneaimd! solution. (29)

Three hundred ml. of freshly prepared tabutylmngnesiun bromide under
nitrogen was cooled in an ice bath. Seventy ml. of a solution of 50 g.
of diocxnne in 100 m1. of other was added slowly with stirring and the
mixture was permitted to reflux. After addition of the dioxene the thick
white paste was stirred vigorously for .1: to ten hourl. The nixturs
was centrifuged for fifteen minutes at 1500 rpm. If the supernatant
liquid was not cleer on testing, seven ml. of ether—dime solution was
added to each bottle, and it was recentrifuged. The supometent liquid
was titrated by the Gilmn (26) method end stored under nitrogen. The

average concentration was 0.30 - 0.35 H. (29)

W!

1. Thereoctions of epoxides with low concentrations of tohutylnagneeium
hromide.’

e. The eddition of t-butylmegzeaium bromide to propylne oxide at
atmospheric pressure (open system).

A small round-bottom flee}: equipped with e mercury—scaled stirrer,

“ppm funngl, . nitrogen inlet, end 3 condenser with I d1? ICC-MOM

 

‘ ii: moot of the polymerization: and purifications of polymers, the various
enoxideo were treated alike. Thus, the procedures described are applicable
for all muonsrs.

"finger" was cooled in on ice bath and swept with nitrogen. The re-
quired amount of propylene oxide was admitted through the dropping fun-
nel, allowed to cool, and then the catalyst was added all at once from a
pipet while the mixture was stirred vigorously. 'I‘he reaction was exo-
thermic and a white precipitate imoediately formed. {the mixture was
stirred for twenty—four to forty-eight hours. The material in the flask
was collected and the unreacted monomer use pemitted to evaporate.
Yields were very low since such or the propylene oxide was lost by
evaporation. Also, it was not possible to be sure that water end oxygen
were excluded from the reaction. Therefore , to prevent contamination and
to insure against monomer loss, it was decided to run the polymerisatione
in a closed system. The increased pressure of a closed system would favor

formation of polymer in accordance with Le Chatelier's Principle.

b. Polymerization in a closed system.

The required amount of monomer was placed in a clean. dry pressure
bottle, which was being mpt with nitrogen ltd “pt in an ice bath.

The t-butylmagaesims bmndde was added as rapidly as possible and the
bottle was imedistely capped. It was then mechanically shaken for about
thirty hours at room temperature.

The best means of excluding oxygen and water from the reaction and
of preventing evaporation of monomer was to add the monomer and catalyst
to a pharmaceutical bottle by means of hypodermic syringes. (30) To
have a true mass polymerisation, the Grignard solution was injected into
the nitrcgm-filled bottle and the ether was removed by suction through
a Moder-mic needle. Then the rumour was injected all at once inte the
catalyst containing bottle. The bottle was mechanically shaken for about

eighty hours or until polymerization was complete.

10.

Since high preee‘urea were built up in the bottles (especially when
the monomer was ethylene oxide), the mum; safety preeeutiene were
tek‘en; the fluke were well cooled during addition, glasses or gorglee
were were, screens were pieced Md the bottles when they were not in
the eheker, end 3 wire eereen lee placed over the bath eenteining the
bettlee which were being shaken. The battles were eo constructed that

the rubber diaphragm could withstand considerable preseure.

2. The fleetiene of epoaddee with anhydrous magnesium branide etherete.
The general procedure at eleeed system pelvpriution ee mentioned
preview}: was followed. The monomer was generally added to the negneeium
bromide. The reaction we vigorous.
In the eqnimolar reectiane the relieving procedure for hydrolyeie
m twee-ea (31) After may hears eheking the bottles were W m
lee end opened. They contained e flocculent preeipit ate and eupemet ent
solvent. Fifty te 75 m1. of eetureted ’ moraine bromide «solution twee
ended nicely with etirring. The ether eelutian wee decanted end the lug--
mime We. and mu s... mm with sum 25 .1. portion e! ether.
The solution end mhmgs 9mm mama and dried m. eodime mm...
The bremehydrin vaei then colleeted by vacuum distillation.

3. The reactions of epoxidee with varying Consultations of di-t-butyl-
magnesium. ‘

The previously described clued eyetem method use follmd. The re-
lation use not vigorous. A white cloudineee seen eppeered 1n the eelntion,
end if polymerization occurred it was usually evident after twelve or lose

hours of eheking. '

11.

Wfim

The polymer was removed from the reaction bottle and meterinl adher-
ing to the sides of the bottle wee moored by rinsing with chloroform,
A lerge excese of chloroform en added to the polymer until ell but the
inorganic materiel had dissolved end the solution was of e fairly low
viscosity. The ineolnble inorganic material was separated by centrifuging
the solution for fifteen minutes at 1500 rpm end decanting. The bulk ef
the chloroform was distilled off, The very viscous licpid was then added
with stirring to an ounce” of diethyl ether to precipitate the higher-
molecular weight polymer fraction. '2‘he eolid was collected by auction
filtration or centrifuging, end the ether use driven from the liquid frac-

tion.

Detemgtigg of W Yigcooitz £29. W m. (32)

Two-tenthe to 0.5 g. of polymer was eccuretely weighed in e tered
fifty milliliter volumetric flask end the flock wee diluted to volume at
20° C, with the eolvent, Aliquots ef this eolution were diluted to vari-
ous concentrations between 0.1 and 2 g,/lOO ml. of solution,

Exactly 5 ml. of polymer solution at the ebove temperature woe placed
in the Oetweld viscometer which was immersed in the constant temperature
beth, The liquid was then drawn by alight suction from en eepireter past
the top mark of the viscometer, The time required for the liquid to flw
between the nerkc woo amretely measured, Viecosity readings were token
until they were constant for the eolution being tested, The epecific

viecoeitiee 71”“ four or five concentrations of the polymer solution

were calculated from the equetiom

‘sz ' . J." OLWAEZ _"_8_0lvs_n§ t : time in eee.

~ t'oolwm'xt

12.

The intrinsic viscosityl‘n1wu ebtained by plotting Tex/cone. egeinst
concentration and ecctrepcleting te zero emcentretien.
The molecular weights of the ethylene oxide polymers were estimated

by substituting the intrinsic viscosity in the Standingger expression
[’n] * m

Kbenzene 3 h.l x 10" (9)

In those viscosity deteminatim where carbon tetrachloride was

the solvent, the following expression was used:

['71] m + K' (32)

xCCZL 3 0.833105

1;

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23.

.T-ZSULTS

1. Results from the use of Wtylmgnoeium bromide catalyst.

There was e very poor yield of e red oil not: the open system re-
action between propylene oxide end t-butylmmosium bromide. This pro-
cedure wee supplanted by the closed system method of polymrisetim.

Ethylene oxide polymerized most readily end yielded e send-solid
pesto or Van'solid depending upon the «mat of solvent end catch-t
mmtretion. This materiel was functionally precipiteted into en
unwoun- viscous liquid end en ether-insoluble waxy solid. In ben-
sene, the liquid fraction had on intrinsic viscosity of 0.02 to 0.03,
proportionel to e moleculer weight of 500 to 850. The solid fraction had
on intrinsic viscosity in hensene of 0.06 to 0.08, preportimel to e
moleculer weight of 1500 to 2000. he” poly-ere were readily soluble in
water, disco-no, elcohol, beam, end chloroform they were sparingly
soluble in acetone and carbon tetrachloride. Of course, high Iolecular
weight {motions were insoluble in diettwl other md petrolm other.

Pmpylene oxide yielded primarily on where-soluble liquid poly-er
fraction with on intrinsic viscosity of 0.015. It was sparingly soluble
in voter end dissolved reedily in nest orgenie solvents except petroleum
ether.

Mada-n. mend. {creed en enamels? viscous, dork, solid-liquid
poly-er which use soluble in ethyl elcchcl, chloroform, end eeetone,
slightly soluble in carbon tetrachloride and benzene, but insoluble in
petroleum the! aid water. The polymer was purified by dielolflng it in

ether. The mreoctod monomer was distilled from the other solution.

21¢.

Pslyoxystyrene in 25 to 30% yield with en intrinsic viscosity of
0.02 was produced-when t-mtylnagaesium bromide see used so cstalyst.
When more than 0.05 mole of catalyst was used per mole of monomer, the
reaction booms moontrollsbls. All three catalysts gave very similar
polymers of styrene oxide. They were ell very viscous yellow guns with
en intrinsic viscosity of 0.02 end were soluble in other, benzene, end
chloroform, end insoluble in water and petroleum ether. A very smell
want of higher molecular weight polymer wes'fomed from this mouse-
uhen di-t-butylmmesiun was used so cotelyst.

2. Results from the use of nemesiue brenids ostelyot.

When semesium bromide was used es s cetelyst for epoxide poly-crise-
ticn, considerable difficulty was encountered in containing the reaction
when the catalyst concentration was beyond 0.05 moles per mole .r‘ mm.

A red, viscous, other soluble liquid was obtained with ethyl-1e oxide.
The intrinsic viscosity was rather low (0. 1 - 0.03) end V" PWPOPUOfld
to e molecular weight of 300 to 700. Like the other liquid polymers forn-
ed in this work, the uteriel could not be distilledevcn «8150’ 0. end
3 m. ssrcury. lt was not very soluble in voter. A gas yield of ethyl-
.s trashydrin use obtained from equiooler reaction.

The propylene oxide polymer produced with anhydrous seguesiun bromide
etherate was. similar in appearance to the polymer from the action of t-
butylmagncsium bromide. The intrinsic viscosities were identical. A 505‘
yield of the bremohydrin was obtained free equinolar reaction of propylene
catids and magaesium bromide.

Polybutsdiene monoxide produced by means of magnesium bromide cetelyst

use siniler in sppesrence, solubility, and viscosity to those mtadiene

25-

mcnoxide polymers produced by the notion of t—butylnagnesium bromide.

The yield was increased if the solvent was removed from the catalyst.

3. Results from the use of dM—Mtylmgnesium catalyst.

Polyethylene-oxides of e very high molecular weight were obtained
in e short time when ethylene oxide was added to di-t-butylmaguesiun.

The other insoluble polymer was a tough, white, fibrous materiel resemb-
ling crude cellulose acetate. It had an intrinsic viscosity in benzene
of 0.6 - 3.6 which represents e molecular weight of 16,000 to 90,000.
The polymer was soluble in ureter, chloroform, benzene, and dioxane end
insoluble in carbon tetrechloride, acetone, diethyl other end petroleue
other. i very small encmt of other soluble liquid was obtained. Its
intrinsic viscosity was 0.05 ( molecular weight: 12%.) '

No polymers of propylene oxide were obtained when di-t-butylmagnesium
was used as e catalyst. Higher catalyst concentrations should have been
tried.

Poor yields ( 6 - 75) of other soluble polymr of butsdiene monoxide
were isolated when dint—butylmsgnesium was used es 3 catalyst.

In almost all cases it was noted that the polymer yield was increased

when the catalyst solvent was removed before monomer addition.

26.

DISC!) 3310!;

1. Optimum conditions for polymerization.

a. Tertiary butylmsgnesiun.bronide as catalyst.

The polymers of ethylene oxide most clearly illustrated the effect
of varying polymerization conditions, such as type of catalyst, catalyst
concentration, solvent effect and polymerisation time.

When t-butylmmesiun bromide in ether was used against ethylene
oxide the total yield was 66 - 68% between catalyst concentration of
0.6 - 5J1 moles per mole of monomer. However, the wt of ether-solu-
ble low molecular weight polymer increased and the amount of ether-
inseluble polymer decreased with increasing catalyst concentration.

The molecular weight of the ether-soluble polymer does not appear
to be dependent upon catalyst concentration. lie generalisation can be
made concerning the effect of catalyst concentration on the ether-in-
soluble polymers since different solvents were used for viscosity mee-
suremente.

When the monomer was added to the dry catalyst and shaken, the yield
increased considerably. When the monomer-catalyst ratie was greater than
1/0.0l the polymerization was quantitative with the higher molecular
weight polymer predominating.

Propylene oxide was polymerized by the action of t-butylmagneeiul
bromide to give a thirty to forty percent fi‘ieli’ef a viscous red oil. (9)
Preliminary experiments indicated that catalyst concentrations greater
than 0.]. sale per Isle of monomer resulted in little or no polymer.
Instead the yield appeared to increase with decreasing catalyst concen—

tration. The optimum catalyst concentration under the experimental

27.

cenditione eet forth in Table 1-8 was between 0.01. end 0.1 of e mole per
mole of monomer. The molecular weight (E ’33: 0.015) did not eppeer to be
dependent upon catalyst concentration.

The optim catalyst concentration for the polymrization of outa-
dim monoxide is about five mole percent. Higher catalyst concentra-
tione caused almost exploeive polymerizetion with comidereble decompoei-
tion. Poor yields were obtained when eolvent was present, but true moo
polymerization resulted in e quantitative Yiflldg

E'he polymers of styrene oxide obtained by moons of tumtylnegnesiun
bromide were ell other soluble end of very nearly the some intrineie
viecoeity. Since thie woe the ceoe, moleculer voight did not seem to be
e function of the cetelyet ooncmtretion. The optima: cat abet concen—
tration wound to be between 0.02 end 0.05 e! e mole of cetelyet per
mole of monomer. The reaction you very vigorous above e catalyst con-

castration of five mole percent..-

b. Anlvdroue nagneeium bromide no oetalyret.
The optima! eetelyet concentration for the production of the low

intrinsic viscosity polymer from ethylene oxide eppeore to be in the
neighborhood of three mole percent; Polymerization in the cold may have
had one effect in coming e higher mlemler-weight polymer; but einc'e
thie polymerizetioo factor woe not intensively investigated, it ie not
et e11 certain whether this in the case. The decreased voter eolubility
competed to other ethylene oxide polymer-e was probably due to bromine

nd groups on the polymer chaine. (9)
The beat catalyst concentration for the production of polypropylene

28.

oxide by means of magnesium bromide was between 0.05 end 0.]. moles HgBrz
per mole of monomer. I

A true moss polymerization and a catalyst concentration nee! five
mole percent eppesred to be the best conditions for the polymerization of

butsdiene monoxide and styrene oxide by the action of magnesium bromide.

0. Use 'of di—t-butylnegnesium as catalyst.

me highest yield of high molecular weight poly-maul.” wee eb-
teined et 0.01 or 0.05 of e mole of cetelyst per mole of monomer. when
the solvent was removed the em catalyst concentretion produced still
higher yields” The time required for polymerisation was mch shorter
then when t-hutylmgnesium bromide was used es s catalyst. A estisrectory
shaking period seemed to he eround twenty-four hours. The intrinsic vie-
coeity roughly increasedwith decreasing catalyst concentretion. Alee,

e considerable Inount of ether-soluble low moleculer weight polymer re-
sulted froze the true moss polymerization. The munt decreeeed with de-
creasing catelyet concentration.

Propylene oxide and butadiens monoxide ‘did not polymerize et the
catalyst concentrations used. Higher catalyst concentretione using the
solvent evaporating technique should be tried. _

Effective polymerizetione of styrene and. with dict-Imtylmegneoium
would require e monomerbcetolyet ratio greater than 130.05. It is in-
teresting to note that polyoxystyrene produced by the use of di-t-butylp
magnesium had the some intrinsic viscosity es polyomtyrene produced by
the use of t-butylmagnesium bromide. while the corresponding ethylene

and. polymers differed remarkably in that respect.

29.

2. Possible mechanisms of polymerization.

The strained three—nembored ring and the two lone pairs of electrons
on the oxygen atom should be expected to give the epoxide group some
chemical properties similar to those of the double bond. One of these
properties is the tendency toward polymerization.’

Thus, like uterine, epoxides should be polymerized both by free
radical and by ionic reactions. Though these two types of polymerization
reactions may be represented in quite different ways, they both operate
by bringing about the addition of a univalent group to one end of e
molecule, and thereby generate e univalent free radical, or free ion,
whereby the addition process can be continued.

Both types occur by means of a chain reaction consisting of three
main stepse initiation, propagation, and termination. The polymerisa-
tion of ethylene oxide with acid catalysts such as sulfuric acid, slump
inun chloride or atannic chloride probably proceeds as fillers: (33)

‘+
CH3 - on H -—s c - CH2
\ I 2 * "i I (initiation)
0 0‘4.
definz
ca-cn ,cn Ho-ca ecu -0!
{12’032 d 2 2 ‘ca2
O... CH:
3 (propagation)
‘* .
moon2 - “deli? ‘ 1:, mo - on, - cnz)In - o - CH2 .. on, x
2 .

(tornination)
The homolytic or free radical polymerization of ethylene oxide‘

probably occurs in a manner analogous to the polymerization of elefins.

first, a free radical is formed from the catalyst (e.g. from a metal
alkyl or organic peroxide) 3

(0235)th .J ‘ 0235' * Pb ’
CIA e
(3&1!redo—04:04:19!5 2 6‘qu + zco2

to CH2 - on2 9" mafcuz-o'

l ,. .
o (initiation)
re ‘ . d '- o
RVH2~CH2-0 + 03% .../(:H2 Ron2 euro-032.0324
O 0 (propagation)
R(CH2-CH2-O)nCH2-,-Ch20- 4- n- -—-> R(Cfl2-CH2-O)naCHZ-CH2CR
(termination)

It is evident that polymerization caused by magnesium bromide ether-
ate is ionic in nature. In the light of the work of Ribae and Topic (31.),
end Huston and Agett (35), it probably proceeds thus:

ee ( )'.
N 2C «CH .__._8 M. OCH-C

O (initiation)
we
Mg(ocuz-caz)2 4. 2n “‘0’ c112 —...\ ug[mu2-cn2.(ocarcnafl;
(propagation)
mg [00112-0324 0011241191] 1- 2 Br uiocnz-ca 2)n-ocuz-cnz.er 2
. (termination)
In cation-catalyzed polymerisation the presence of the catalyst in
the molecule attached by a coordinate palace as on ergonoxnetallic com-

pound is indicatel by Stoudinger'e observation (9) that polystyrene pre-

pared with otni'mic chloride no the'catalyst is difficult or impossible to

31.

free from catalyst by precipitation from inert solvents, but the use of
alcohol readily frees the polymer from tin and chlorine. This could
readily be accounted fOr according to this formulation!

c1 Sn ”smog! -—-*c1
l‘ 5 “Caz-Eocéns A Cthn

cargo-é a "‘

(:1 Sn on on - H --" c on an cm H + 2101
h [ 21:3 2 E “5 6::{6 “36:15

.‘h 6

%gflg :2-5HCI

since the organonetallic end group would undergo scission in a solvent
containing active hydrogen, and the SnCl3 group would be replaced by
hydrogen. (33) The difficulty encountered in purifying the msgnesium
bromide-catalysed polymers is also explainable by the preceding types of
mechanism» This cationic mechanism is further verified by the fact that
only low molecular weight polymers were produced. This is a distinguish-
ing characteristic of ionically initiated polymerizations.

Thet type of mechanism involved in the polymerization with t-butyl-
magnesium bromide and di-t-butylnsgnesiun is not so simply ascertained.
The differences in molecular weight observed in the various types of poly—
ethylene oxides indicate that the reactions must have proceeded by dif-
forent mechanisms.

Beaman (21) proy>osed an anionic mechanisn for the polymerization of

nethacrylonitrile by means of butylmagnesiun bromide, triphenylmsthyl so-

diun.end sodium in liquid auuonil.

- 3
A: + (mfg r—A MHz-g: (initiation)
. a. '
.3 g h R.—
A-CH : nC " ’ 'l" A CH -C H : (propagation)
2 m n:- ' 2 n 2 12'
‘ R R._ +, ' '
. 82—6 CH 1 -+ H __; A H - H (termination)
hi 2 O 2 i' .
e1 . flit!
¢

(A: t initiating negative fragment, e.g. PhBCz)

(R ' Electron withdrawing group)

(R' 5 H or some other substituent)

(The termination reaction may occur in some other manner,

. such as elimination of A4-.)
He assumed that the ionic nature of the Grignerd reagent and of triphenyl-
methyl sodium made it.seem highly unlikely that these reagents should re-
act by honolytic cleavage to yield free radicals in the presence of highly
polar monomers. Immediate and quantitative polymerization of methacrylo-i
nitrile in liquid ammonia offered more direct evidence for an anionic
mechanism. He also surmised that if the reuction were free radical, butc-
diene and styrene would be expected to polymerize readily. The failure te
obtain any polybutadiene and only low molecular weight polymer from.styrene
can be explained from the point of View of the anionic mechanism because of
of the relativel y'weak electronegctive character of a vinyl or phenyl
group.
Application of en inicnic mechanism to the polymerization of epoxides

with t‘butylmsgnesiun bromide seems applicable in light of the results of
this research. Ethylene oxide is particularly noteworthy. It is highly

polar with two lone pairs of electrons at the oxygen atom, This would

result in carbon atoms of en electrophilic nature. The analogous mechanism

 

33.

can be written thus!

(CH3)’C? + Wie‘ (engrcnz-cnz-o'
(Cfl3)30-;CH2-CH2-O.'P n W 4 (CH3)30(ca2-cnzgo)ncnrcu2-o’
(CH3)3C-(CH2-CH2-O)n-CH2-CHTO.+ 3*» (C}{3)30-(CH2~CH2-O)-H

The low'molecular weight of the products obtained is typical of ionically
catalyzed polymerizations. Higher molecular weight products in greater
yield than magnesium bromide catalyzed polymers is evidence egainet the
cationdtype mechanism. The less satisfactory results from.the use of the
other monomers may possibly be due to their lower polarity3

The very high molecular weight of the polymers obtained by the use of
di-t—butylmagneaium on ethylene oxide seems to indicate that polymeriza-
tion may have occurred by a mechanism different from that with the full
Grignard.

A free-radical catalysis may have been possible since the t-butyl
radical has A low free energy of formation. (36) In the absence of highp
l! ionized magnesium bromide, this free radical formation may have taken
precedence over the ionization of the elkyl. (see p. 30.)

This work is only In introduction to the subject of polymerization
of epoxides by means of Grignard reagents, The results indicate that
further intestigetions into this field should be quite worthwhile. The
effects of‘vnrying temperature, pressure, and solvent concentration should
be studied. The effects of higher concentrations of catalysts should be
determined for those epoxides which are not readily polymerized at lower

catalyst concentrations. The structure of the polymers of butadiene

3h.

monoxide would be another interesting problem (See page 3.)

Is the search for new monomers is e notch-ending project, I. the
meet for new and different polyurisution initiators i111 elm! Oeu-
time no long «the desire for poly-ere with special properties is

high.

SUPREME

1. Tertiary butylasgnesium bromide, magnesium bromide ethercte, end
dietertisry butylmsgnesiun.uere investigated as possible catalysts for
the holyuerieetion of certain epoxidee (ethylene oxide, propylene oxide,
butediene monoxide and styrene oxide).

2. Tertiary butylmagnesiun‘brouide use found to be an excellent catalyst
for the production of low molecular weight polymers of ethylene oxide.
Poorer yields of polymers were obtained when pronylene oxide, hutediene
'nenoxide, and styrene oxide were the nononere.

), Hagneeium.broaide produced fair*yields of leH'molecular weight poly»
more from :11 the epoxides used.

.h. Di-tertiary butylnsgnesiun effected the production of high molecular
weight polymers of ethylene oxide. At the concentrations used, it was
ineffective against propylene oxide and butsdiene oxide and caused e poor
yield of low molecular weight polycrystyrene.

5. The optimum cetalyst concentrations umre determined, and the effect
of solvent was studied.

5. Possible polymerization mechanisms were discussed.

(13
(2)
(3)
(u)
(5)
(6)
(7)
(8)
(9)

(to)

(11)
(12)
(13)
(1h)
(15)

(16)
(17)
(19»)
(19)
(20)
(21)

(22)

36.

131313.00va
Stoudinncr, H. and Schweitzer, 0., Ber. £1131, 25195-21405 (1929).
1.9. Parbcnind. 1.0., Brit. 3116.550 (1930).
1.0. Forbenind. 1.<:., Fr. 750,520 (1931).
Fran: Webel (to 1.6. Farbonind. 1.6.), 0.9. 1,921,37811933).
Mn Uituer (to 1.6. Fsrhenind. £43.), U.3. 1,976,678 (19310.
LG. Fan-behind. 1.11., Germ. 597,1.“ (1931.).
1.6. Ferbenind., Brit. ~06,AA3 (1931).

McClelland, C.P. end Between, R.I.., Chem. Eng. New 31, 2A? (1916).

Stmdinger, H., Koch T'olek'xlare Organ-133cm Verbindungcg, J. Springer,
331.11“; (1932) Po 287'332e

Bloor, R.R., Pogo-negation 91 Butgdiene We. Master's Thesis,
Michigan State College, 19%.

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