SPHERULITES OF CIS-1,4-POLYBUTADIENE - MOLECULAR-WEIGHT EFFECTS

Morphological features of melt crystallized cis-1,4-polybutadiene were examined by means of polarized light microscopy. Samples similar in b ranching characteristics but different in molecular weight (MW) were s tudied. High MW samples exhibited features of dwarf spherulites. Sampl es of lower MW formed spherulites of radial texture at low crystalliza tion temperatures (T-c), spherulites of banded texture at intermediate T-c, and spherulites of complex birefringence at the high T-c end. Mi croscopic observations during subsequent heating of the latter spherul ites indicated that they were composed of a mainframe of the banded te xture and interstitial crystallites with different orientation. The in terstitial crystallites melted at a lower temperature range whereas th e 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 crysta llization.