Cross-Linking of Polymers: Kinetics and Transport Phenomena

The cross-linking process of a complex system was studied at elevated temperature. Partially hydrogenated poly(acrylonitrile-co-1,3-butadiene)/dicumyl peroxide compound was selected as a representative complex polymer/cross-linking agent system. On the basis of the mechanisms of cross-linking reactions, an expression relating reaction rates and population balance equations with rheologically determined concentration of cross-links was applied. Consequently the Eyring equation reflecting the effect of the self-diffusion on reaction rate constants was utilized and was further integrated into the classical Arrhenius equation for reaction rate constants. Diffusion coefficients acknowledging the mutual diffusion were estimated according to the free-volume theory, whereas thermodynamic properties governing the heat transfer, i.e. density, heat capacity, and thermal conductivity, were determined from independent measurements. Plateau storage modulus variation was monitored within the linear viscoelastic regime by dynamic mechanical analysis. Compounds with different initial peroxide concentrations were chosen for the study of the correspondence between model predictions and experimental observations, which proved to be very good.