Characterization of signals in the solution1H NMR spectrum of poly(isobutylene-co-p-methylstyrene) and their utility

Poly(isobutylene-co-p-methylstyrene) is an important precursor to Exxpro™ elastomers. A previous report detailed the characterization of both the proton and the carbon NMR spectra of the copolymer.1 However, several resonances in the proton NMR spectrum of the copolymer were not assigned. Specifically, the proton methine resonance of the BSB triad sequence is now identified and used to calculate BSB triad contribution to the copolymer microstructure. This report describes the assignment of this resonance and other resonances associated with microstructural sequence distribution around p-methylstyrene. The proton NMR signals of interest resonate at 2.8 ppm and 2.5 ppm in a typical spectrum for poly(isobutylene-co-p-methylstyrene). The nature of these resonances were determined by preparation and characterization of specifically deuterated poly(isobutylene-co-p-methylstyrene)s employing both one and two dimensional NMR techniques. The 2.8 ppm signal is assigned as the methine proton of a p-methylstyrene incorporated between two isobutylene units (the BSB triad). The signal at 2.5 ppm is assigned to the meso-BSS triad. Determination of these resonances allows for rapid evaluation of isolated p-methylstyrene units (BSB triads) present in the copolymer using only 1H NMR. The utility of this technique is demonstrated by comparing BSB triad values determined by 1H and 13C NMR analysis. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1680–1686, 2000