Self-plasticization of polymers

Abstract

Using varying proportions and different combinations of polystyrene fractions with degrees of polymerization 928, 222, 48, 39, 8, 3.3, and 2, twelve mixtures of widely varying composition were prepared. The same conclusions could be drawn from the volume-temperature curves of these mixtures as were drawn from the data for pure fractions in an earlier paper. Regarding the thermal expansion coefficients ( dv/dT) liq. and ( dv/dT) sol. and the specific volumes above the transition temperature υ liq., the mixtures behave as ideal mixtures composed of chain end and middle groups. The end groups act as plasticizers and cause the “self-plasticization” of the polymer. From the fact of an “iso-oscillation volume” at the transition temperature, a relationship between second-order transition temperature, T g , and the mole fraction of the end groups, N e , was derived. An explanation is given for the statements of Alexandrov and Lazurkin that high polymers plasticized by their monomers show softening temperatures which are independent of the molecular weight of the high polymer and depend only on the percentage of monomer.