Copolymers of Butadiene with Halogenated Styrenes C. S. MARVEL, G. ESLER INSKEEP, AND RUDOLPH DEANIN C'niversity of Illinois, Urbana, I l l .
A. E. JUVE, C. H. SCHROEDER, .iND AI. M. GOFF The B . F . Goodrich Company, Akron, Ohio Some twenty halogenated styrenes have been copolymerized with butadiene in a typical emulsion polymerization formula. Based on laboratory evaluations of small samples, the quality of most of the copolymers was approximately equivalent to that of GR-S. There were indications that the copolymers containing 2,Sdichlorostyrene, 3,4-dichlorostyrene, and p-cyanostyrene were superior to GR-S in several respects.
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S S E E K I K G nen copolymers of butadiene nhich night show rubberlike properties superior to those of the styrene copolymer, the authors were led by numerous reports on chlorostyrene derivatives ( 4 ) t o make a study of halogenated styrenes. The chlorostyrenes are potentially available in quantity and should be reasonablj cheap. The present work was undertaken to obtain fundamental information on the copolymerization of these halogenated styrenes n i t h butadiene as well as to learn what relative advantages and disadvantages the various copolymers nould have as substitutes for rubber. I n addition to various halogenated styrenes the copolymerization of p-cl-anostyrene and some derivatives is included in this report. The methods of preparation of the new halogenatcd s t l iencs have been reported elsewhere (13). The known compounds were made by the standard methods The mixed mono-, di-, tri-, and tetrachlorostyrenes were furnished by the Electrochemical Department of E. I. du Pont de Kernours R: Company, Inc. The 2,5dichIorostyrene was furnished by the Monsanto Chemical Company. POLY MER1 ZATION
Most of the monomers were charged a t a 25:75 w i g h t ratio with butadiene in a t,ypical emulsion polymerization recipe and polymerized as nearly as possible to 7 7 5 conversion. -k fen of the more promising styrenes n-ere also tested a t a 15: 85 rat,io and a t a rat,io of x:75, whcre x is the molar equivalent of 25 parts of styrene. Halogen analysis showed to what extent the styrene had entered the copolymer. Table I s h o w that some of t,he monohalogenated styrene copolymerizations went at a slightly slower rate than did the control. Thus o- and p-chlorostyrenc, vi- and p-fluorostyrene, and nr-bromostyrene gave a slou-er over-all ratc ; on the other hand, 7%-chlorostyrehe, the mixed chlorostyrenes, and 0- and pbromostyrenc gave a normal conversion in 11 hours. It is pOSsible that traces of inhibiting impurities in the monomers Tvere responsible for some of these anomalous results. hniong the dichlorostyrenes the 2,3-, 2,4-, and mixed isomers had a normal rate; the 2,B-isomer slowed tbc polymerization considerably; and &he 2,s- and 3,4-isomers (on the basis of data not shown) copolymerized somewhat more rapidly than styrene. The triand tetrachlorostyrenes gave progrcssirely slorver polymerization rates. Very little pentachlorostgrciie appeared in the
copolymer. p-Cyanost yrene copolymerized normally. a-Chlorostyrene caused the emulsion t o break, perhaps because the halogen alpha to the ring was no longer protected by its position on an olefinic carbon atom once polymerization had begun, so that it. was h>-drolyzcd to give hydrochloric acid; in any event, the breaking of the emulsion prevented any appreciable polymer formation. Thc ratio a t n-hich the two niononiers enter a copolymer is quite significant in relation to the properties of the product', for it dcterniines whether there is homogeneity of structure from one molecule to the next. Wall (15) has defined the value CY as the exponent in the equation:
%
=
(Z)"
where n2 and nyare the nuniber of unpolynierized inoleculeb of two monomers, x and y, after a given time of polymerization has elapsed, when n: and 11," molecules of the two monomers were present at the beginning of the reaction. Wall points out that only in an ideal copolymcrization, \vtiei
