INSIGHTS INTO THE CURE CHEMISTRY OF BROMINATED BUTYL RUBBER

Abstract

ABSTRACT The importance of dehydrobromination to the cure chemistry of brominated butyl rubber (BIIR) is demonstrated through a combination of cure rheometry studies and model compound experiments. These data show that, while HBr elimination to give an exomethylene conjugated diene is inevitable, subsequent reactivity is highly sensitive to acidity within the mixture. As a result, formulations containing acid scavengers such as epoxides or MgO produce cure dynamics and yields that differ markedly from those of unstabilized analogues. These differences in allyl cation reaction pathways underlie much of the known behavior of BIIR + ZnO compounds and have a substantial effect on the progress of sulfur-based cure formulations. In this report, allyl cation fragmentation and electrophilic addition mechanisms are developed from 1H nuclear magnetic resonance (NMR) and mass spectrometry analysis of model compounds, and their implications for sulfur, ZnO, and sulfur + ZnO vulcanization chemistry are detailed.