Abstract Both static and dynamic thermomechanical techniques have proved to be useful in elucidating effects of molecular structure and morphology on the behavior of poly(vinyl chloride). Indeed, such methods are sometimes sensitive to rather small differences in, for example, crystallinity. In this paper, the current literature is reviewed, with emphasis on the relation between stereoregularity, crystallinity, and mechanical relaxation behavior. In order to interpret results of recent studies, simple models are then proposed for the typical morphologies encountered. Most experimental facts are consistent with the existence of very small plate-like crystallites, with intercrystallite spacings being inversely dependent on crystallinity, and, in turn, inversely dependent on polymerization temperature.