TOUGHENING OF POLYSTYRENE AND POLY(PHENYLENE OXIDE) MATRICES WITH ELASTOMERIC STYRENE-BASED BLOCK COPOLYMERS - ROLE OF MOLECULAR ARCHITECTURE

The effects of the molecular architecture of elastomeric styrene-based block copolymers on efficiency of toughening a brittle (polystyrene) and a ductile [a miscible blend of 80% phenylene oxide copolymer and 20% polystyrene (80PEC)] polymer were explored experimentally. Toughening appears to be mainly controlled by the blend morphology, which is determined by the rheological characteristics of the block copolymer relative to that of the matrix. The formation of dispersed particles during melt blending in a Brabender Plasticorder is strongly influenced by the ratio of the matrix and block copolymer viscosities (estimated here by Brabender torque). The size of the dispersed particles was found to be proportional to the 1.77 power of the torque ratio when this ratio is greater than unity. Thus, to a first approximation the effect of block copolymer architecture on toughening efficiency is related to how this structure affects the rheological behavior of the copolymer. Excellent toughness of polystyrene was achieved when the particle size was larger than 1-2-mu-m. The 80PEC resin is best toughened by block copolymers that form a cocontinuous phase morphology. The extent of toughening of this matrix appears to be a strong function of the styrene block molecular weight, whereas this structural feature seems to have no significant effect in toughening polystyrene.