Isothermal crystallization of syndiotactic poly(propylene-co-olefin)s

Isothermal crystallization of syndiotactic poly(propylene-co-olefin)s (olef in = ethylene, I-butene, I-pentene, l-hexene, 4-methyl-1-pentene) was studi ed. The melting behavior of isothermally crystallized polymers was investig ated by differential scanning calorimetry, and the equilibrium melting temp erature (T-m(0)) was determined by Hoffman-Week's plot. Crystallization rat e and Avrami exponent of isothermally crystallized copolymers from the melt were measured by depolarized light intensity technique. The half time of c rystallization (t(1/2)) was found to be dependent on the degree of supercoo ling (Delta T), but independent of the comonomer. The Avrami exponents (n) of copolymers were detected by the Avrami plot and the average n ranged fro m 2.0 to 2.8 for the primary crystallization process in any copolymer. The effect of isothermal crystallization temperature (T-c) on the crystalline s tructure of copolymers was studied by wide-angle X-ray diffraction (WAXD). The WAXD patterns of all the copolymers were similar to the pattern of Cell II in the syndiotactic polypropylene. The WAXD pattern of I-butene copolym er with small amount of I-butene indicated the existence of Cell III. (C) 1 999 Elsevier Science Ltd. All rights reserved.