LABORATORY STUDY OF LOW RATIO BUTADIENE–STYRENE COPOLYMERS

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Abstract
The copolymerization of styrene and butadiene in ratios in which the styrene equals or predominates over the butadiene on a mass basis is essentially similar to copolymerization in the presence of a predominance of butadiene. However, the rate of reaction and the length of the induction period is increased. Increasing the amount of the dodecyl mercaptan regulator results in a slight increase in rate and diminution of the induction period. The dodecyl mercaptan reacts at a lower rate than during the production of GR–S. The regulating index as defined by the ratio of the logarithm of the residual mercaptan over the conversion is 1.53. The bound styrene and increment styrene curves seem to be normal and indicate reactivity ratios r1 (butadiene) equal to 1.4 to 2.2, r2 equal to 0.5 to 0.7. If these reactivity ratios are corrected for the bifunctional nature of butadiene then the constants for butadiene monomer are Q equal to 0.9 and e equal to − 1. Likewise the gel–viscosity data are similar to those observed with GR–S except that the pre-gel rise in viscosity, the formation of gel, and the slope of the viscosity conversion curves diminish with increasing styrene in the charge. The chain transfer action of styrene is increasingly evident with increasing styrene content in the charge but in all cases the regulating effect of dodecyl mercaptan is still apparent.

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