Miscibility and segmental mobility in hydrogen-bonded polymer blends

Water vapour was used as a diffusional probe to study the interaction and segmental mobility in hydrogen-bonded polymer blends. Modified polystyrenes containing p-(hexafluoro-2-hydroxylisopropyl) groups as hydrogen-bond donors were blended with poly(methyl methacrylate) and two styrene-acrylonitrile copolymers. Interaction parameters, estimated from solubilities of water vapour in the blends, were negative in all cases. Positive excess volumes were found for several pairs and were believed to be the result of poor chain packing of styrene and methyl methacrylate or acrylonitrile segments, which were inherently immiscible with each other. In a number of blends, the diffusion coefficients were higher than the ‘average’ values for the component polymers. The deviation in diffusion coefficient was opposite in sign to the deviation in the activation energy of diffusion from its ‘average’ value. The residual activation energy was proportional to the excess volume. Furthermore, an excellent correlation was found between diffusion coefficient and specific free volume.