Intermolecular packing of freely jointed branched polyalkene melts: a microscopic approach

Abstract

Polyalkene melts are modelled using a freely jointed chain model. Intermolecular correlations are investigated for different chain architectures using polymer reference interaction site model (PRISM) theory. A three-site model is used to represent local monomer structures in which the CH₂ and CH sites on the backbone, and the CH₂ and CH₃ sites on the side chains, are considered as hard spheres. For 200 monomer chains of various architectures, we have calculated the six radial distribution functions at a packing fraction of 0.5. The side-chain sites are found to hinder the interchain approaching of backbone sites. These shielding effects are found to be reduced upon adding more backbone sites between the branches. The cohesive energy and isothermal compressibility were calculated for various monomer structures. It is found that the cohesive energy decreases with increasing linearity of the molecular structure. The symmetry of the branching with respect to the backbone is found to play a crucial role in lowering the cohesive energy.