EFFECT OF ABC TRIBLOCK COPOLYMERS WITH AN ELASTOMERIC MIDBLOCK ON THEADHESION BETWEEN IMMISCIBLE POLYMERS

The effect of tyrene-block-poly(1,2-butadiene)-block-poly(methyl metha crylate) triblock copolymers (SBM) and their hydrogenated analogs bloc k-poly(ethylene-co-butylene)-block-poly(methyl methacrylate) (SEBM) on the fracture toughness of the interface between immiscible polymers h as been studied by using an asymmetric double cantilever beam fracture test. The fracture energy G(I) has been investigated as a function of the copolymer interfacial areal density Sigma and elastomer content a s well as the temperature at which the samples were fractured. No rein forcement of the interface was found for a nide range of Sigma for all investigated triblock systems at room temperature. In fact, for a ran ge of Sigma values the triblock was found to weaken, rather than stren gthen, the interface. In addition, it was found that mixing just 25% o f triblock into polystyrene-block-poly(methyl methacrylate) diblock co polymer was sufficient to remove the interfacial toughening effect of the diblock. The triblock copolymers were found to toughen, rather tha n weaken, the interface when the sample was fractured at a temperature below the glass transition temperature of the elastomer. These result s are in agreement with a model that is based on the assumption that i t is impossible to transfer enough stress across a plane glass-rubber interface to initiate crazing in the glassy polymers.