Effects of a Diblock Copolymer on Adhesion between Immiscible Polymers: 1. Polystyrene(PS)-PMMA Copolymer between PS and PMMA

Abstract

Thin layers of polystyrene (PS)-poly(methy1m ethacrylate) (PMMA)d iblock copolymers were placed at the interface between PS and PMMA homopolymers, and the samples were joined at high temperatures. Fracture testa were used to measure the interface toughness, and secondary ion ma88 spectroscopy (SIMS) was used to examine the organization of the diblock. Diblock copolymers with molecular weights of 84 OOO and above gave strong interfaces whose saturation toughness was independent of the copolymer molecular weight. Both kinetic studies and the SIMS results showed that the rate of diblock copolymer organization was a function of the layer thickness. Copolymer layers of thickness greater than about onefourth of a long period did not organize in a simple way at the interface but gave interfaces with a high toughness. For thin layers that did organize, the toughness was low and the diblock molecules broke near their junction points. Low molecular weight symmetric and asymmetric diblocks were shown to give lower toughnesses than the high molecular weight materials, probably because they were pulled out of the PS homopolymer.