Synergistic effect of 4,4′‐bis(maleimido) diphenylmethane and zinc oxide on the vulcanization behavior and thermo‐mechanical properties of chlorinated isobutylene–isoprene rubber

It is well known that the vulcanization of chlorinated isobutylene–isoprene rubber (CIIR) with ZnO alone is very slow and the resulting vulcanizate shows low crosslinking density as well as poor mechanical and thermal properties. For these problems to be addressed, 4,4′‐bis(maleimido) diphenylmethane (BMDM) has been applied along with ZnO to cure CIIR. The curing behavior was investigated using oscillating disk rheometer and differential scanning calorimetry analysis. The crosslinking densities, mechanical, dynamic mechanical, and thermal properties of the vulcanizates were also evaluated as a function of BMDM content. From the rheometer and differential scanning calorimetry analysis, it has been confirmed that the rate of curing, as well as the extent of curing between CIIR and ZnO, has remarkably increased in the presence of BMDM. The Diels–Alder reaction between the in situ formed conjugated diene butyl from CIIR/ZnO with the maleic moieties of BMDM has been identified as a primary reason for the higher rate and state of cure. The crosslinking densities of the vulcanizate CIIR/ZnO have significantly increased with increase in the content of BMDM. As a result, the compression set of the vulcanizate was remarkably decreased at elevated temperature. Moreover, the vulcanizates contain BMDM that has exhibited high thermal degradation temperature and good retention of the mechanical properties even after 7 days of thermal ageing. Copyright © 2016 John Wiley & Sons, Ltd.