Variation of polymer density with molecular weight and consequences in dilatometric studies of addition polymerization

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Abstract
Evidence is presented to show that the molar volumes of a series of liquid oligomers can be adequately represented as linear functions of their degrees of polymerization. This is explained by assuming that the end groups and repeat units make their own independent contributions to the molar volume. On this basis, the density of a linear polymer in the liquid or liquid-like state is determined by the weight fraction of end-groups and the densities characteristic of the high-molecular-weight material and the substance formed by the combination of the two end-groups. In dilatometric studies of addition polymerization reactions in which the average molecular weight of the products increases with time, only the densities of the monomer and high molecular weight polymer are required in the computation of the amount of monomer converted to polymer from the observed volum e change.

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