Multiple melting behavior of syndiotactic 1,2-polybutadiene

A differential scanning calorimetry study on a typical thermoplastic elastomer, syndiotactic 1,2-polybutadiene, crystallized from the melt is presented. Endotherms observed upon heating for samples isothermally crystallized from the melt exhibited a double melting profile. The peak temperature of the endotherm that appeared at a lower temperature (low endotherm) showed stronger dependence on the heating rate than that appearing at a higher temperature (high endotherm.). The results of partial melting experiments demonstrated that the high endotherm is not affected at all by melting of only the crystals responsible for the low endotherm, indicating that the double melting behavior is due to the existence of two crystalline species with different stabilities. Structures and melting mechanisms of these two different crystalline species are discussed on the basis of the observed difference in superheating behaviors upon melting. The results on overall rate of isothermal crystallization are also presented.