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

Morphological features of melt crystallized cis-1,4-polybutadiene (cPB D) were examined by means of polarized light microscopy. Three samples of similar molecular weight characteristics but different levels of l ong-chain branching were studied. The two low-branching samples exhibi ted typical spherulitic morphology. The spherulites were of banded tex ture at higher crystallization temperatures (T(c)); the band period de creased with decreasing T(c) and eventually became unidentifiable at T (c) < ca. -40-degrees-C. The spherulitic growth rate decreased signifi cantly with the increasing level of branching. The effects of long-cha in branching were most dramatically manifested by the surge of small ( ''dwarf'') spherulites in the highly branched cPBD; the dwarf spheruli te stopped growing at a size of several microns and induced new dwarf spherulites among its periphery. The process repeated itself to the ap parent end of crystallization. The melting temperature of slow-cooled or cold-crystallized samples decreased with the increasing level of br anching. These observations were discussed in terms of the entanglemen t concept.