SPHERULITES OF LONG-CHAIN BRANCHED CIS-1,4-POLYBUTADIENE

Morphological features of melt crystallized cis-1,4-polybutadiene (cPBD) were examined by means of polarized light microscopy. Three samples of similar molecular weight characteristics but different levels of long-chain branching were studied. The two low-branching samples exhibited typical spherulitic morphology. The spherulites were of banded texture at higher crystallization temperatures (T(c)); the band period decreased with decreasing T(c) and eventually became unidentifiable at T(c) < ca. -40-degrees-C. The spherulitic growth rate decreased significantly with the increasing level of branching. The effects of long-chain branching were most dramatically manifested by the surge of small (''dwarf'') spherulites in the highly branched cPBD; the dwarf spherulite stopped growing at a size of several microns and induced new dwarf spherulites among its periphery. The process repeated itself to the apparent end of crystallization. The melting temperature of slow-cooled or cold-crystallized samples decreased with the increasing level of branching. These observations were discussed in terms of the entanglement concept.