INTERFACIAL MODIFICATION OF POLYMER BLENDS - THE EMULSIFICATION CURVE.1. INFLUENCE OF MOLECULAR-WEIGHT AND CHEMICAL-COMPOSITION OF THE INTERFACIAL MODIFIER

The effect of several parameters such as molecular weight, chemical co mposition and architecture of the interfacial agent on the dispersed p article size is investigated in polystyrene/ethylene-propylene rubber blends. The study is based on the dependence of the dispersed phase si ze versus the concentration of interfacial modifier, the so-called emu lsification curves. A critical concentration value of interfacial agen t based on the volume of the minor phase was determined beyond which n o further changes in particle size were observed. These results show t hat block copolymers also display an emulsification curve. The influen ce of the molecular weight (from 50 x 10(3) to 174 x 10(3) g mol(-1)) of the saturated triblock oly(styrene-block-ethylene-butylene-block-st yrene) interfacial modifier is demonstrated to have little effect on e mulsification phenomena. The influence of the chemical composition of the interfacial modifier on the shape of the emulsification curve appe ars to be a critical consideration. The presence of double bonds in th e copolymer modifier significantly diminishes its emulsification capab ility. It is interesting to note that, once the emulsification phenome non has been significantly reduced due to the presence of double bonds , imposing a conformational restriction (star-shape architecture) has little effect on the emulsification curve.