Abstract
| - The high pressure (incompressible), high molecular weight limit of the lattice cluster theoryis derived as a first approximation to describe the influence of monomer molecular structure andnonrandom mixing effects on the thermodynamic properties of binary polymer blends. In particular, thenoncombinatorial free energy of mixing and the small angle neutron scattering effective interactionparameter χexp emerge in this limit as rather simple, compact analytical expressions that depend on asingle microscopic energy and on two geometrical indices obtained easily from the monomer united atomstructures. These analytical expressions, in conjunction with the geometrical indices summarized in atable for a wide range of vinyl monomer structures, enable the rapid use of the theory with minor additionaleffort than the application of Flory−Huggins theory. Our theory is applied to a few polyolefin blends inorder (a) to illustrate a new mechanism for the occurrence of lower critical solution temperature (LCST)phase diagrams in incompressible systems, (b) to provide a partial explanation of why blends of poly(isobutylene) with other polyolefins often yields LCST behavior, and (c) to explain the rather large negativeentropic portions of χexp observed for many binary polyolefin blends.
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