Effect of crosslinking on block and random copolymers of styrene and butadiene

The effect of crosslinking on the molecular dynamics of two triblock copolymers and a random copolymer is investigated and compared. Dynamic-mechanical measurements were done to evaluate both real and imaginary parts (J′, J″) of shear compliance in wide temperature and frequency windows. -95 to 120°C and 10-4 to 10 Hz, respectively. Moreover, DSC as well as stress-strain measurements were carried out. The materials used in this study are two triblock copolymers, mainly styrene-butadiene-styrene, (SBS) triblock copolymer, in addition to styrene-butadiene-rubber (SBR) random copolymer. The materials were crosslinked by means of dicumylperoxide (DCUP) up to 10 parts per hundred of rubber (phr) to obtain different crosslinking concentrations. Complete master curves were constructed for all samples and analyzed using Cole-Cole processes. It is shown that crosslinking of block copolymers has a much stronger effect on the dynamics of the polybutadiene (PB) phase in block copolymers than in random copolymers having the same styrene content. The results were discussed using the meander model of Pechhold, and the Mooney-Rivlin and Mullins equations.