Stretching, packing, and thermodynamics in highly branched polymer melts

Within the framework of the polymer reference interaction site model (PRISM) theory, we formulate a simplified method for enforcing conformational self-consistency associated with screening of intrapolymer excluded-volume interactions. It is built on a utilization of the Flory ideality concept, preaveraging of site inequivalency, and the insensitivity of equation-of-state properties of chemically identical polymers to global architecture variation at constant temperature and pressure. The approach allows calculation of the influence of chain branching on average macromolecular stretching under meltlike conditions. Nonideal conformational swelling, intermolecular pair correlation functions, and the cohesive energy as a function of architectural variables have been studied for a variety of star and regular comb models. Predictions for a specific highly globular comb melt are in good agreement with a recent experiment. The relatively weak influence of the nonuniversal local aspect ratio and melt compressibility on polymer stretching is also established. Implications for the χ parameter in isotopic star or comb blends, and the miscibility of mixtures of linear and branched polymers, are briefly discussed.