Bromo Butyl Rubber Cross-linked by Bismaleimide Resins, Curing Kinetics and Properties

Bromobutyl rubber (BIIR) was cross-linked with three bismaleimides(BMI), viz. 4,4'-diphenylmethane bismaleimide (DMB), 4,4'-diphenyloxy bismaleimide(DOB) and 2,2'-bis-4-(4-maleimidephenoxy)phenyl]propane (BMP). The cure kinetics, as studied by isothermal Theological measurements revealed a first order kinetics. The activation energy was the lowest for BMP possessing a flexible backbone. The Ene-reaction between the maleimide and the rubber was facilitated further in this case as it provided a polar medium. The cross-link density was a direct function of the molar concentration of the BMI and the mechanical properties of the vulcanized rubber were dependent on the cross-link density. BMP led to an apparently tougher rubber system by providing a relatively longer spacing between the cross linking chains. The BMI-vulcanized systems showed poor compatibility to corrosive propellants like liquid N2O4 and hydrazine derivatives. Contrary to expectation, the compatibility decreased with increased cross-linking.