Poly(styrene- b-methyl methacrylate) block copolymers as compatibilizing agents in blends of poly(styrene- co-acrylonitrile) and poly(2,6-dimethyl-1,4-phenylene ether): 1. Location of block copolymers in ternary blends — compatibilization versus micelle formation

Abstract

The compatibilizing effect of the symmetric narrowly distributed block copolymer poly(styrene- b-methyl methacrylate) (P(S- b-MMA)) in blends of high-molecular-weight poly(styrene- co-acrylonitrile) containing 20 wt% (PSAN20) or 43 wt% acrylonitrile (PSAN43) with poly(2,6-dimethyl-1,4-phenylene ether) (PPE) was investigated by dynamic mechanical spectroscopy and transmission electron microscopy. In blends with the PSAN43, P(S- b-MMA) forms spherical micelles in the PPE phase with no dispersing efficiency. In contrast to this, for blends with PSAN20, the block copolymer is located at the phase boundary, causing an extremely fine dispersion of the components. Depending on the location of P(S- b-MMA), the PPE glass transition is altered by the PS blocks to different degrees. Even for block copolymer concentrations as high as 20 wt%, in ternary blends with PSAN20 and PPE no micelles could be detected. The results suggest that A/B blends compatibilized with a C-D block copolymer, in which the copolymer components show an exothermic heat of mixing with the bulk phases A/B, are superior to systems A/A-B/B with respect to emulsifying efficiency. Owing to the high tendency of the block copolymer to locate at the phase boundary, micelles do not compete at concentrations of practical interest.