Crystallization in stretched polymer networks. I. trans‐polychloroprene

Measurements are described of the rates of crystallization of uncrosslinked trans‐polychloroprene over a range of temperature and of three crosslinked samples over a wide range of extension and temperature. The large increases in rate with extension are attributed to corresponding increases in the equilibrium melting temperature and hence degree of supercooling. The rise in melting temperature has been measured and is found (1) to account satisfactorily for the observed changes in rate, and (2) to be in good agreement with Flory's treatment of oriented crystallization in stretched networks. The form and magnitude of the changes in tensile stress are also in accord with the formation of oriented crystallites, and seem incompatible with folded‐chain crystallization. When reduced to a condition of constant segmental mobility, the rates of crystallization are shown to follow a common dependence upon the degree of supercooling. This relation is compared with the predictions of nucleation theory.