科研之友
微信
新浪微博
Facebook
分享链接
摘要
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 degrees 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 (similar to 30%) when M-w was increased from 122 to 934 kg/mol. At low R's (< 10 degrees 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) 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 alpha) 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.
- 出版日期2008-3-5
- 单位中国石油大学（北京）
