Synthesis, Bromination and Cure of Isobutylene/Isoprene/P-Methylstyrene and Isobutylene/Isoprene/Styrene Terpolymers

Abstract

Abstract High molecular weight isobutylene/isoprene/p-methylstyrene and isobutylene/isoprene/styrene terpolymers containing up to 10.6 mol% p-methylstyrene and 3.6 mol% styrene were synthesized using “H2O”/AlCl3 as an initiator/coinitiator system in methylchloride at -95 °C. p-Methylstyrene was found to be uniformly distributed in the chains due to its similar reactivity to isobutylene. In contrast, styrene had a lower reactivity than isobutylene or even isoprene, resulting in low conversion of the styrene monomer. The reactivity ratios obtained were in good agreement with the published values. Up to about 3 mol% styrenic monomer content, the Tg of the terpolymers showed no significant increase. The isoprene units of the terpolymers were brominated by the conventional bromination technique. During bromination, some of the aromatic rings also underwent bromination. The extent of this reaction was found to be much lower in the case of p-methylstyrene than in the case of styrene. The brominated terpolymers were cured using ZnO. The brominated terpolymers displayed much faster cure, higher maximum torque and modulus at the same brominated isoprene concentration than brominated copolymers of isobutylene and isoprene, indicating that the aromatic rings participate in the cure. The brominated terpolymers showed an increased resistance to hot air aging, compared to brominated polymers containing no styrenic termonomer.