EFFECT OF MONOMER STRUCTURE AND COMPRESSIBILITY ON THE PROPERTIES OF MULTICOMPONENT POLYMER BLENDS AND SOLUTIONS .3. APPLICATION TO PS(D) PVME BLENDS

Comparisons between lattice cluster theory predictions and experiment for thermodynamic properties of compressible blends are presented for the specific case of PS(D)/PVME blends. These comparisons are also used as part of a more general study of the influence of monomer structure and compressibility on the properties of polymer blends. A series of 12 different vinyl monomer structures is used to examine how monomer structure affects the effective interaction parameter, chi-eff, from extrapolated zero-angle experimental neutron scattering and the heat and volume changes upon mixing. When the effective interaction parameter is evaluated in the incompressible limit for 66 model blends that differ only in the monomer structures, the slope of the composition dependence of chi-eff is found to range over several orders of magnitude. Using one adjustable parameter, the microscopic exchange energy, only four of the model blends are in rough accord with both the temperature and composition dependences of the PS/PVME neutron scattering data of Han et al. A consideration of the heat of mixing serves to differentiate strongly between these four cases and emphasizes the need for several different types of measurements on the same system if interest lies in obtaining meaningful microscopic information concerning structure and interactions in polymer blends. The nonzero experimental values for the volume change on mixing provide a stimulus for extending the lattice cluster theory to compressible blends where the three van der Waals energies serve as the only adjustable parameters. Certain blend properties are again shown to be very sensitive to the monomer structures. Residual discrepancies between lattice cluster theory predictions and experiments provide insights into theoretical and experimental studies to unravel further the influences of monomer structure and interactions on the bulk thermodynamic properties of compressible polymer blends.