THE COMPOSITIONAL HETEROGENEITY OF BUTADIENE-STYRENE COPOLYMERS SYNTHESIZED AT −18°C. IN EMULSION

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Abstract
A study has been made of butadiene-styrene copolymers formed at −18°C. From analyses for bound styrene in the product for various conversions and initial butadiene-styrene ratios the reactivity ratios were calculated to be r1 = 1.37 and r2 = 0.38 compared with 1.8 and 0.6 at 45°C. Q and e for butadiene were 1.38 and 0.008 relative to styrene at 1 and −0.8. Increment bound styrene curves calculated for each stage of the reaction indicated that the polymers were remarkably homogeneous at low conversions. The chain transfer reaction using mixed tertiary mercaptans as the modifier was studied. Regulating indices were found to have decreased with polymerization temperature. Number average [Formula: see text] and viscosity average [Formula: see text] molecular weights were calculated from mercaptan disappearance and vistex intrinsic viscosity data respectively. The molecular weight heterogeneity increased with increasing conversion and initial mercaptan content. The increment number average molecular weights were found to diminish with conversions, whereas the increment viscosity average increased at higher conversions as conversion increased.