The influence of monomer structure on the thermodynamic properties of polymer melts and solutions is explored in Monte Carlo computations. The internal energy, the specific heat, and the chemical potential are determined for united atom lattice models of polyethylene, polypropylene, polyethylethylene, and polyisobutylene, all with M=60 united atom groups. Computations are performed for a range of melt volume fractions 0<φ⩽0.7 and effective temperatures 3.3⩽T*⩽∞. The results reveal fine differences between the internal energies of the four different melts (solutions) and a pronounced influence of monomer structure on the specific heat and the chemical potential. The computed thermodynamic quantities are confronted with the analytical results of the lattice cluster theory (LCT). It is shown that for most thermodynamic states the LCT correctly predicts the qualitative effect of monomer structure on the thermodynamic quantities. However, large errors observed in the LCT values for the specific heat, and a qualitative departure between simulation and theory for the difference between the internal energies of polyethylethylene and polyethylene, stress the need both for improvements in the analytical solution of the LCT and for further tests of its accuracy.

Topics
Lattice models, Thermodynamic states and processes, Thermodynamic properties, Monte Carlo methods, Polymers, Chemical compounds
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2002
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