Temperature and Rate Effects on Crystalline Transitions in cis-1,4-Polybutadiene as Measured by DTA

Abstract

The crystallization temperature, Tc, and the crystalline melting point, Tm, of cis-polybutadiene are strongly affected by the rate of sample cooling and heating. Cooling at rates of five to several hundred °C/min and subsequent heating at rates less than about 20 °C/min results in two distinct crystalline melting peaks. Outside this range of cooling and heating a single crystalline melting peak is observed. One of the peaks is at —9° C, which is the value generally reported in the literature, while the second peak was found to decrease with increasing cooling rate to a value of —35° C for a cooling rate of about 200 °C/min. When the cooling rates are increased, the crystallization temperature is also observed to decrease. The lowest value of Tc detected was — 61° C, at a cooling rate of 65 °C/min. This is in contrast to the literature value of — 35° C. These data are interpreted in terms of the rate processes of crystallization reported by Wood and Bekkedahl on natural rubber.