Theoretical predictions on the configurations of polymer chains in the amorphous state

Statistical mechanical models used to treat mixtures of random-coiling polymer chains with solvents invariably lead to a partition function that can be separated into a factor for the intramolecular configurations of the chains and another factor for mixing with solvent. It follows that the average configuration of a chain should be independent of composition, and hence the same in the bulk polymer as in a dilute solution, apart from effects of excluded volume. Whether this prediction is a figment of idealized models is the issue in question. Critical examination shows the predictión to be independent of details of models, and hence lends strong support to the implications of past theory. In short, difficulties of packing chain molecules to bulk density are not alleviated by partial ordering. Hence, a chain of sufficient inherent flexibility should assume random configurations unbiased by neighboring chains. Experimental evidence from rubber elasticity, cyclization equilibria, and the thermodynamics of polymer solutions provides compelling evidence for random configurations in amorphous bulk polymers. The basis for the assertion that the effect of excluded volume on the average molecular configuration must vanish in the bulk polymer is reviewed here.