Polymer blend miscibility
A number of quasi-binary homopolymer blends have been investigated with regard to their miscibility. The blends consisted of poly(epichlorohydrin) (PEPC) mixed with a range of poly(methacrylate) polymers:- poly(methyl methacrylate); poly(ethoxyethyl methacrylate); poly(tetrahydrofurfuryl methacrylate) and poly(glycidyl methacrylate) (PGMA). It was found that the state of mixing of the systems varied with the structure of the ester side chain, embracing a number of miscibility states. It has been postulated that the observed miscibility in the system PGMA/PEPC is due to the presence of a small specific interaction between the species. A second category of blend investigated comprised of a homopolymer (PEPC) and a random copolymer. In two cases the copolymers (styreneco- methacrylonitrile; methyl methacrylate-co-methacrylonitrile) were chosen such that the cohesive energy density of PEPC lay between those of the comonomers. This led to the observation of a number of miscibility states for the systems, depending upon the copolymer composition. Analysis of these systems and similar examples in the literature was conducted using the mean-field approach. A reasonable accord between theory and experiment was found when the role of both specific interactions and free-volume terms was negligible. A third type of copolymer (glycidyl methacrylate-co-methyl methacrylate) was found to be only partially miscible with PEPC. This was due to the small GMA/PEPC interaction and the tendency of the copolymer to diverge from the copolymerisation equation at high GMA concentrations. The experimental probe for miscibility has been the glass transition temperature. This was determined using Differential Thermal Analysis, Dynamic Mechanical Thermal Analysis and to a lesser extent, Dielectric Relaxation. The phenomenon of partial miscibility, in which phase composition varies with overall blend composition, has been discussed. It has been postulated that this widely observed behaviour is due to a non-equilibrium phase separation process. The inadequacy of existing relationshi in describing the variation of the glass transition temperature of a miscible blend with composition has been highlighted. Furthermore, the importance of the transition width as an indicator of miscibility has been stressed.