Nonisothermal crystallization of s-PP fractions

✍ Scribed by Junting Xu; Linxian Feng; Zhengxi Liu; Linshen Chen; Yi Deng; Chunming Cui; Wei Chen

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 120 KB
• Volume: 71
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19990207)71:6<897::aid-app5>3.0.co;2-9

✦ Synopsis

Syndiotactic polypropylene (s-PP) was prepared by metallocene catalyst and was fractionated with the temperature rising elution fractionation (TREF) technique. The nonisothermal behavior of the obtained fractions was investigated. Fractions was first cooled at different rates and then heated at a constant rate. The parameters such as the peak crystallization temperature (T c ), the onset crystallization temperature (T on ), the difference between T on and T c (⌬T 1 ϭ T on Ϫ T c ), the crystallization enthalpy (⌬H), the peak melting temperatures (T m1 , T m2 ), and the difference between the T m1 and T m2 (⌬T 2 ϭ T m2 Ϫ T m1 ) were obtained. The dependence of these parameters on cooling rate, syndiotacticity, and molecular weight was discussed. It is found that T c , T on , ⌬H, T m1 , and T m2 systematically increase with increasing syndiotacticity and are depressed on increasing the cooling rate. Cooling rate, syndiotacticity, and molecular weight show different influences on ⌬T 1 . In the melting process of s-PP, double peaks were observed.