PROCESSING AND MORPHOLOGY OF POLYSTYRENE ETHYLENE-PROPYLENE RUBBER REACTIVE AND NONREACTIVE BLENDS/

The difference between reactive and nonreactive polymer blends in term s of processing and morphology has been investigated. The glassy phase s for the blends are an oxazoline functional polystyrene (PS-Ox) and a similar non-functional polystyrene (PS). The rubbery phases are an et hylene-propylene rubber (EP) and a similar ethylene-propylene rubber ( EP-MA) with 0.7% grafted maleic anhydride. In the case of PS-Ox/EP-MA blends, the oxazoline group may react with the grafted rubber function ality at the interface between the two immiscible components during bl ending to form a compatibilizing agent in-situ. The nonreactive blend systems of PS-Ox/EP and PS/EP-MA were used for comparison to the react ive system. The blend components are theologically matched to simplify the interpretation of the process and morphological data, The blends were prepared in a batch mixer with roller blades. The torque required for mixing was measured during the blending process. The torque trace s for the reactive blends exhibited a peak in torque, attributed to th e chemical reaction at the interface. The weight fraction of gel in th e blends was used to measure the extent of reaction. It correlates wel l with the mixing torques and theological properties. The nonreactive PS-Ox/EP and PS/EP-MA. blends show poor interfacial adhesion between t he two phases. In contrast, the reactive PS-Ox/EP-MA blends show excel lent adhesion and smaller dispersed domain sizes. The stability of the morphology during annealing is also much greater for the reactive ble nds. Varying the functionality concentration in the PS phase shows tha t the dispersed phase rubber particle size is reduced by increasing th e concentration of oxazoline in the matrix. Blends with no or small am ounts of functionality in the PS phase exhibit yield behavior in tensi on. However, a level of concentration of reactive functionality may be reached where the material becomes brittle.