Control of morphology and properties in multicomponent polymers based on polystyrene/polyester block copolymers

The morphology and properties of multicomponent polymers based on polystyrene/polyarylate block copolymers (PS-b-PAr) are investigated. The PS-b-PAr molecule was synthesised by a novel procedure using carboxy terminated polystyrene. The architectures of the PS-b-PAr copolymers were predicted by a kinetic simulation model. Based on the results of the simulation and analysis of morphology, both the optical and mechanical properties of the PS-b PAr are explained. The domain size, which dominates the transparency, was found to be sensitive to the purity of the block copolymer, while the birefringence was determined not only by the PS/PAr ratio but also by the length of each segment. On the basis of the experimental analyses, conditions were designed for the synthesis of PS-b-PAr copolymers with high transparency and low birefringence. The mechanical properties of the PS-b-PAr were controlled by modification of the miscibility between the PS and PAr segments. Acrylonitrile was introduced into the PS chain as a miscibility modifier. The volume fraction of the interfacial layer increased with the increase in miscibility. In particular, around the acrylonitrile concentration at which the miscibility reaches a maximum, the flexural strength was dramatically improved, changing the fracture behaviour from brittle to ductile. Furthermore, the PS-b-PAr copolymer was used as a compatibiliser for several immiscible polymer blend systems, including high impact polystyrene-polycarbonate and polyamide 6-acrylonitrile/butadiene/styrene. In these applications the PAr unit was used not as a macromolecular anchor but as a reactive unit. The experimental results showed that PS-b-PAr could compatibilise these blend systems effectively via an in situ reaction between the PAr chain and either polycarbonate or polyamide 6 during the melt mixing process.