Charakterisierung von Vulkanisaten aus bromierten Poly-(isobutylen-co-4-methylstyrol) durch Festzustand-NMR
von R. R. Eckman, I. J. Gardner u. H.-C. Wang
The curing of brominated poly-(isobutylene-co-4-methylstyrene) was studied using solid-state magic-angle-spinning NMR, a technique which is uniquely suited to investigate cured or crosslinked polymers. This brominated copolymer contains 4-bromomethylstyryl and 4-methylstyryl functional groups and was compression cured with pure ZnO. It was proposed that a precomplex is formed between zinc and the 4-bromomethylstyryl group, which generates a benzylic carboationic intermediate. Crossslinking predominantly occurs by alkylation of the phenyl ring of another 4-bromo-methylstyryl group by the benzylic intermediate. The ZnO brings the two bromides of these groups into proximit. The dependence of the cure chemistry on the concentration of 4-bromomethylstyryl functional groups was studied. Conversion of some 4-bromomethylstyryl groups to oxygenated species upon curing was also observed.