Influence of block composition on crack toughness behaviour of styrene-b-(styrene-random-butadiene)-b-styrene triblock copolymers

The deformation and fracture behaviour of symmetric and asymmetric styrene-b-(styrene-random-butadiene)-b-styrene (S-SB-S) triblock copolymers with variations in their molecular architectures in terms of their outer PS block and the random SB middle block composition ratios have been investigated using essential work of fracture approach based on post yield fracture mechanics concept. The present investigations on crack resistance behaviour of these S-(S/B)-S triblock copolymers where effective interaction parameter (χ_eff) is systematically varied through the variation of block compositions and architecture is in continuation to our earlier communicated short article highlighting the phase behaviour-morphology and mechanical property interrelation. The crack initiation and propagation behaviours are correlated to morphology and dynamic mechanical properties as obtained from TEM, SAXS and DMA measurements. The influence of interaction parameter (χ-parameter) space which has been manipulated through the variation of block compositions has clearly manifested in their morphologies and in their mechanical properties. Further the kinetic aspects of fracture mechanical response have also been investigated where all the materials have clearly revealed block composition dependence. SEM analysis was carried out to understand the fracture modes prior to failure.