Effect of steric restrictions on the enhancement of miscibility through hydrogen bonding in blends of modified poly(α-methyl styrene) with polymers containing acceptor sites

Two series of copolymers have been prepared from a-methylstyrene and a-methylstyrene units modified by the incorporation of the hydrogen-bond donor untis, methyl carbinol and trifluoromethyl carbinol, designated PaMS (1) and PaMS (II), respectively. It has been observed that if the concentration of the donor unit exceeds 4 mol %, one-phase blends can be prepared with a series of polymers containing hydrogen-bond acceptor sites such as poly(vinyl acetate), poly(vinyl pyrrolidone), poly(4-vinyl pyridine), and some poly(alkyl acrylate)s, none of which are miscible with the unmodified PaMS. All the one-phase blends formed are stable at temperatures above the glass transition temperature, T_g, of the blend, but eventually phase separate when the temperature is increased sufficiently. These lower critical cloud-point curves have been measured for a wide range of the blends and act as an indicator of the effectiveness of the hydrogen bonds in enhancing one-phase blend formation. The T_g's of the blends are in many cases higher than those calculated from the simple rule of mixtures and reflect the reduction in chain mobility in the blends caused by extensive hydrogen bonding. The results demonstrate the effect that specific interactions have in enhancing miscibility in binary polymer blends.