Enhancing the efficiency of zinc oxide vulcanization in brominated poly (isobutylene-co-isoprene) rubber using structurally different Bismaleimides

It is a known fact that the bromobutyl rubber can form carbon-carbon crosslinks when it is heating with zinc oxide at a temperature greater than 160 °C. Generally, the rate of ZnO vulcanization is slow at this temperature. If any, attempt to enhance the rate of cure by rising the temperature will lead to an inferior state of cure. It has also been reported that heating of halobutyl rubber with ZnO at higher temperature produces conjugated diene butyl prior to the formation of carbon-carbon crosslinks. In the present work, we tried to exploit the possibility of Diels-Alder reaction between the in-situ formed diene butyl and the maleic moieties of bismaleimide to enhance the rate and extent of curing between BIIR and ZnO. For that, BIIR was heated with ZnO in combination with two types of bismaleimides such as N, N′ m-phenylene dimaleimide (HVA-2) and 1,3-Bis(citraconimidomethyl) benzene (Perkalink 900) in different concentrations from 1 to 5phr. The vulcanization studies using oscillating disk rheometer and isothermal scanning calorimetry have proved that the state and rate of curing in BIIR with ZnO have significantly enhanced in the presence of these bismaleimides. However, the efficiency of HVA-2 towards improving the state and rate of curing was considerably higher than that offered by Perkalink 900. The lowest activation energy for HVA-2 from the cure kinetic analysis confirmed the higher activity of HVA-2 over Perkalink 900.