Computation of Heat Capacities of Liquid Polymers

The liquid heat capacities at constant pressure of a series of linear polymers have been computed as the sum of vibrational, external, and conformational contributions. Most of the heat capacity of liquid macromolecules arises from vibrational motion. The external contribution is assumed to approach zero at constant volume. The conformational contribution, finally, is calculated using a fit of experimental heat capacities, as available from the ATHAS data bank, to a one-dimensional Ising-type model with two discrete, degenerate states. A stiffness and a cooperativity parameter permit the representation of the experimental data for polyethylene, polypropylene, poly(methyl methacrylate), poly(n-butyl methacrylate), and polystyrene. Agreement between computation and experiment lies within a few percent, close to the experimental precision.