Crystallization and Melting Behavior of trans-1,2 Syndiotactic Polypentadiene

1,2-Syndiotactic polybutadiene was synthesized at -30degreesC using the catalyst system CrCl(dmpe)(2)-MAO. The syndiotactic index of the butadiene sequences, expressed as a percentage of syndiotactic pentads [rrrr], was evaluated by C-13-NMR measurements. WAXD and SAXS techniques were employed to characterize the crystalline structure of the polymer. The thermal behavior of the polybutadiene was investigated by differential scanning calorimetry. The isothermal crystallization kinetics were described by means of the Avrami equation, which suggested a three-dimensional growth of crystalline units, developed by heterogeneous nucleation, followed by a secondary crystallization stage. Polybutadiene isothermally crystallizes from the melt according to regime 11 of crystallization described by Lauritzen-Hoffman secondary nucleation theory. Nonisothermal crystallization kinetics were elaborated using the Ziabicki and Avrami methods modified by Jeziorny. The equilibrium melting temperature was calculated.