Abstract
The effect of weight‐average molecular weight (M~w~) on the nonisothermal crystallization kinetics of linear metallocene polyethylene (m‐PE) was studied with modulated differential scanning calorimetry. Six linear m‐PEs of molecular weights in the range 122–934 kg/mol were prepared by gas‐phase polymerization. The cooling rate (R) was varied in the range 2–20°C/min, and it significantly affected the crystallization behavior. M~w~ had a weak influence on both the peak crystallization temperature and the crystallization onset temperature. All m‐PEs showed primary and secondary crystallizations. At both low and high R's, the crystallinity showed a significant drop (∼ 30%) when M~w~ was increased from 122 to 934 kg/mol. At low R's (< 10°C/min), the rate parameters in the modified Avrami method [primary rate constant (k~R~)] and Mo method [F(T)] of analyses agreed in suggesting that an increased M~w~ slowed the rate of crystallization. The M~w~ dependency of k~R~ followed the Arrhenius type (k~R~ = k~Ro~e^281^/M~w~, where k~Ro~ is a rate‐dependent constant). However, at higher R's, k~R~ approached a constant value. The order parameters obtained by the different methods of analysis (n and α) were independent of M~w~, which suggests that the crystal type remained the same. Hoffman–Lauritzen theory was used for data analysis, and activation energy per segment showed a significant decrease, from 225.0 to 11.8 kJ/mol, when M~w~ was increased from 152 to 934 kg/mol. Finally, all methods of analysis suggested a significant effect of M~w~ on slowing the overall crystallization process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008