Crystallization in stretched polymer networks. II. Trans‐polyisoprene

Abstract

AbstractMeasurements are described of the rates of crystallization and crystal melting temperatures in stretched test pieces of trans‐polyisoprene, crosslinked to various degrees. The increase in rate with extension are attributed to the corresponding increases in melting temperature and hence degree of supercooling. The rise in the melting temperature of both the α‐ and β‐crystal forms is found to be in satisfactory agreement with Flory's treatment of oriented crystallization. The changes in tensile stress are also generally in accord with the formation of oriented crystallites. For the more lightly crosslinked materials, a pronounced rise in tensile stress occurred during the later stages of crystallization, at extensions below about 100%. Reasons are given for attributing this phenomenon primarily to the relatively large contraction in volume on crystallization, rather than to the formation of folded‐chain crystallites.