THE POLYMERIZATION OF ISOPRENE AND 2, 3-DIMETHYLBUTADIENE AND COPOLYMERIZATION WITH STYRENE AT −18 °C. IN EMULSION

The rate of polymerization increased with purification of the monomers. It was possible that the dienes formed cyclic compounds or dimers in side reactions. The 1,2 addition of the monomer decreased with decreasing polymerization temperature. A study was made of the copolymerization of isoprene and dimethylbutadiene with styrene at −18° C. From analyses of bound diene in the product at various conversions and initial diene to styrene ratios the reactivity ratios for these diene-styrene systems were calculated to be r1 = 1.30 ± 0.02 and r2 = 0.48 ± 0.01 for isoprene and styrene and r1 = 0.92 ± 0.02, r2 = 0.42 ± 0.02 for dimethylbutadiene and styrene (styrene always being considered monomer 2). Q and e values from the Alfrey-Price equation were calculated as Q = 119 and e = −0.112 for isoprene and Q = 1.09 and e = −0.181 for dimethylbutadiene relative to Q = 1.0 and e = −0.8 for styrene. Fom these and the values previously determined for butadiene, reactivity ratios for all combinations of the three dienes were calculated. The chain transfer reaction between dienyl radicals and mixed tertiary mercaptans was studied and it was found that isoprenyl and dimethylbutadienyl radicals were much more reactive than butadienyl. The effect of this was illustrated by number and viscosity average molecular weights. Intrinsic viscosities of homo- and copolymers formed in a mercaptan-free recipe were measured and compared.