Spherulites of cis-1,4-polybutadiene: molecular weight effects

Abstract

Morphological features of melt crystallized cis-1,4-polybutadiene were examined by means of polarized light microscopy. Samples similar in branching characteristics but different in molecular weight ( MW) were studied. High MW samples exhibited features of dwarf spherulites. Samples of lower MW formed spherulites of radial texture at low crystallization temperatures ( T c), spherulites of banded texture at intermediate T c, and spherulites of complex birefringence at the high T c end. Microscopic observations during subsequent heating of the latter spherulites indicated that they were composed of a mainframe of the banded texture and interstitial crystallites with different orientation. The interstitial crystallites melted at a lower temperature range whereas the mainframe persisted to higher temperatures. The melting temperature of slowly cooled or cold-crystallized samples decreased first but then remained approximately constant with increasing MW. These observations are discussed in terms of the entanglement effects during melt crystallization.