Novel observations on morphological changes in polyesters induced by blending with small concentrations of polymer diluents.

Unexpected morphological changes have been found in a number of aliphatic polyesters (poly(epsilon-caprolactone) and the suberate, azelate and sebacate polyesters of ethylene glycol) upon blending with small concentrations (~1%) of polar polymeric diluents, notably poly(vinyl butyral) and poly(vinyl chloride). Among these changes are striking reduction in frequency of nucleation of spherulites, marked enhancement in regularity of lamelar organization in banded spherulites (also manifested by improved regularity of banding), modification of lamellar thicknesses and melting behavior, and modification of molecular packing in crystals. It is believed that adsorption of diluent on crystal boundaries (growth faces and fold surfaces of lamellae) underlies most of these effects. Possible implications with respect to other polymer blends are discussed briefly.