Melting Temperature of Mixed-Microstructure Polybutadiene

Polymerization of butadiene with lithium alkyls in hydrocarbon media produces a chemical microstructure with roughly equal amounts of 1,-cis and 1,4-trans units and a lesser amount (~8%) of 1,2 (vinyl) units. The high molecular weight versions of those polymers appear to be amorphous at all temperatures. For example, no calorimetric evidence has been reported for a phase transition from the glass temperature, T_g~ -99 °C, to temperatures in excess of 100 °C. This absence of crystallinity seems reasonable in view of the mixed microstructure and similar results for other copolymer-like systems such as stereoirregular polystyrene. The purpose of this note is to report some observations on low molecular weight polybutadienes with this microstructure which suggest the occurrence of crystallization at low temperatures.