REACTIVE REINFORCEMENT OF POLYSTYRENE POLY(2-VINYLPYRIDINE) INTERFACES/

The effect of reactive compatibilization on adhesion at the interface between the immiscible polymers polystyrene and poly(2-vinylpyridine) was investigated. Reactivity was incorporated into the system by light ly sulfonating the polystyrene component, providing acid functionality which is coreactive with the basic pyridine nitrogen. The interaction between sulfonic acid and pyridine groups generates interchain cross- links and therefore compatibilizing graft copolymers. The reinforcing effects of in-situ copolymer generation on the interface were quantifi ed by evaluating interfacial adhesion through measurement of interfaci al fracture toughness using the asymmetric double cantilever beam test . Interfacial properties were assessed as a function of the concentrat ion of sulfonic acid groups present. The results show that the toughne ss of the interface is dramatically improved by the incorporation of r eactivity, increasing from similar to 2 J/m(2) in the unreactive syste m up to >150 J/m(2) in the reactive system. At long reaction times, th e toughness of the reactive interface approaches that of pure polystyr ene. Approximately 5-7% sulfonation was found to produce optimum mecha nical reinforcement. Scaling relations between the amount of compatibi lizer formed at the interface and interfacial fracture toughness sugge st that the copolymers formed act to initiate interfacial crazing duri ng failure, accounting for the enhanced adhesion.