Phase Behavior of Polystyrene and Poly(n-pentyl methacrylate) Blend with Small Amounts of Symmetric Polystyrene-block-poly(n-pentyl methacrylate) Copolymers

Abstract

The phase behavior of polystyrene and poly(n-pentyl methacrylate) (PS/PnPMA) blends with small amounts of symmetric PS-block-PnPMA copolymer (PS-b-PnPMA) was studied by turbidity, light scattering, and small-angle neutron scattering (SANS). At ambient pressure, PS/PnPMA with lower molecular weights exhibited both the upper critical solution transition (UCST) and the lower critical solution transition (LCST), and with increasing molecular weights of PS, an hourglass type of phase behavior was observed. When a very small amount (∼0.5 wt %) of symmetric PS-b-PnPMA is added to the blend, LCST increases but UCST decreases. This indicates that the miscibility window is expanded, and the PS-b-PnPMA acts as an effective compatibilizer in the PS/PnPMA blend. However, when the amount of symmetric PS-b-PnPMA is larger than a critical amount which depends on the molecular weight of block copolymers, the turbidity temperatures (Tb) for the LCST are essentially the same regardless of blend compositions. Thus, the turbi...