4566
C. G . OVERBERGER, D. TANNER AND ELI X. PEARCE [COSTRIBUTIONFROM
THE
DEPARTMENT O F CHEMISTRY, P O L Y T E C H N C ISSTITUTE
Vol. 80 O F BROOKLYN]
Ionic Polymerization. Copolymerization of Nuclear and Side-chain Alkyl-substituted Styrene Monomers1 BY
c. G. OVERBERGER,D. T.LNNER~ AND ELI h1. PEARCE' RECEIVED
FEBRCARI:
1i, 19\58
Cor~'~lyiiierizatioii of nuclear arid side-chain alkyl-substituted styrene monomers has been used as a method for determining the relative steric effect for the addition of a n ion pair t o a n olefinic double bond. Monomer reactivity ratios are reported for the copolymerization of C Y - , 8- and p-alkyl-styrenes with a reference monomer (p-chlorostyrene) and show the following order of reactivity: a-methyl > p-methyl > p-ethyl > styrrne > trans-@-methyl> cis-@-methyl> @-ethyl. - I n iriterr~retatiiiiiof results in terms of steric factors, li~-perconjugatioiland liroxinlity to the reaction site is given.
Most 1 , l da- and l,%"-disubstituted ethylenes show a reluctance to add to themselves during attempted free radical polymerizations. This is generally attributed to steric effects which are clearly demonstrated in copolymerization studies. In contrast to free radical polymerization, steric effects have not received any extensive study in cationic polymerization. Recent kinetic studies on the cationic polymerization of a-methylstyrene showed an abnormally low propagation rate due to steric factors..' P-hkthylstyrene polymerized less rapidly than a-inethylstyrene under the influence of acids and this may be attributed to enhanced steric effects.> The successful cationic polymerization of these methylstyrenes probably is due to the ability of the methyl group to sufficiently activate the double bond toward reaction with an electrophilic carbonium ion so that steric effects play a small role. The purpose of this research has been to correlate the size and location of the alkyl groups on the styrenes with the extent of steric domination of their reactivities during cationic polymerization. To investigate these steric effects quantitatively, cis- and trtzns-,~-methylstyrene,P-ethplstyrene (predominantly the trans isomer), 3-n-propylstyrene and p-ethylstyrene were copolymerized with p chlorostyrene as the reference monomer and stannic chloride as the cationic catalyst. X convenient synthesis of isomer-free a- and 8alkylstyrenes from the acetates of appropriate carbinols has been reported in a separate paper.O
Experimental Solvents and Catalyst.-Carbon tetrachloride, uitroberizene and stannic chloride were purified and ampules of the latter prepared according t o procedures described previo~sly.~ Monomers.-0-hlethyl-, @-ethyl- and 0-n-propylstyrenes were prepared by pyrolysis of t h e acetates of t h e appropriate carbinols.6 cis- and trans-p-methylstyrene were (1) This is t h e 11th in a series of papers concerned with ionic polymerization. For the 10th paper in this series, see C. G. Overberger, 1- A n g a n d 11. Mark, J . Pniyinri, S r i . , 111 press (1958). ( 2 ) .4 portion uf theses uf I1 l'anner and E. 31. Pearce submitted 111 partial fulfillment of the requirements for the degree of Doctix r>f I'hilosophv in the (:r;rduate Schonl crf the Polytechnic Institute c ) f Arooklyn. (3) 1. Alfre?, Jr., J. J . Bohrer and W AIark, "Copul?merizati(Jn." Interscience Publishers, Inc., S e w York, K , 17., lY5'2, (a) p. 7 i j . ( b ) 1). 49. (4) D . J. Worsfold and S. Bywater, THISJ O U R K A L , 79, 4917 (19.57). ( 5 ) J . XT. Van der Zanden and T . R. Rix, Rec. t?av. chiin., 75, l l l i i i iIiJ.5tj). lii) C . (: Overherper anrl I1 Tanner ' T F t I S 1 1 7 1 - n N A l . . 77, R e i ) 1B,j5) ( 7 ) C. G. Clverberger. L . H . .Arond and J . J . Taylor, i b i d , 73. 5.541
,
(1991).
heparated 1))- distillation through a spinning baud coluriin of over ,50 the{iretical plates; cis-S-methylstyrene, b.p. %Xio (15 miii.), U ~ 1.5430, ~ D 15:; yield of olefin mixture obtained, A,,,;,, 242 n i p , log E 4.12, A ,,,:, 280 m p , log E 2.51 (57yc yield, b.p. 52.1" (12 rrim.),7zZ0~ 1.543U,d2u,0.902,by decarboxylation of ti.a~zs-2-methyl-:',-phenylprr~penicacid)*; trans-8rnethylst)-renc, b.p. 71' ( 2 5 mm.),~ i 2 5 1 1 1..%80, 85'p of olefin iiiisturc obtained, A,,,,, 2-19 nip, log E 4.222; A,,:, 283 mp, log e 3.01 (Tc; yield, b . p . 53' (8 mln.), n S 0 D 1.%(17, ciaO? 0.902,115- dehydration of l-phen?-l-l-propariol).fi )-Ethylstyretie was prepared from p-ethylbenzene using the Perrier n1odificatim of the Friedc.1 arid Crafts reaction tu obtain the ketone,g reducing the latter with lithium duiiiirium hydride and dehydrating the resulting carbinol wiih piitassiurn hisulfate.10 From 80 g . of p-ethylphenylinetliylcarbinol was obtained 45 g. (MyG)of p-ethplstyrerle, 1).p.4O0 (1 min.), 1125,511 1.5349 ()-ield 8 5 r i , b.p. 68' (10 inin.). I Z ~ ~1.5350, D prepared by vapor phase dehydratllnl over activated alumina) .g ,b-Chlcirv~tyrenewas purified as previously described Polymerization Technique.~--The polymerization teclitiique throughout \vas identical t o that described by Overherger, Ehrig atid Tanner.l1 Coriversioiis were calculatetl from the weight of p(~lyll1er olitained. The following formula was used to correct .\I: for conversions above 6c;
.'
.if2 = ' 1.-
+
11,' ~
,)
lii.1
- --
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