Critical molecular weight for block copolymer reinforcement of interfaces in a two-phase polymer blend

Abstract

The effect of a small addition of poly(styrene-b-2-vinylpyridine) block copolymer on the microstructure and mechanical properties of phase-separated blends of polystyrene (PS) and poly(2-vinylpyridine) (PVP) was investigated. Only copolymers whose PVP block degree of polymerization was above 200 were found to be effective in preventing failure at the interface. This critical value corresponds roughly to the molecular weight between entanglements M e , suggesting therefore that at least one average «entanglement» between the PVP bhlock and the PVP homopolymer is necessary to have good stress transfer at the interface