Microtacticity of polypropylene fractions produced by different active sites of heterogeneous Ziegler–Natta catalyst

✍ Scribed by Junting Xu; Yiqing Yang; Linxian Feng; Xiangming Kong; Shilin Yang

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 389 KB
• Volume: 62
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19961031)62:5<727::aid-app2>3.0.co;2-y

✦ Synopsis

Polypropylene (PP) prepared with the MgC1z/TiC1,-A1Et3/PhzSi(OMe)2 catalyst system was fractionated by a preparative temperature rising elution fractionation (TREF) technique in the wide temperature range of room temperature to 13OoC. The results of fractionation showed that there were plural active sites in this heterogeneous catalyst. Some key fractions were selected for characterization of 'Hand 13C-NMR. 'H-NMR results suggested that the fractionation takes place according to tacticity. Based on analysis of 13C-NMR, it was concluded that the polymerization mechanism proceeding on highly stereospecific active sites was active site-controlled and nonstereospecific active sites were able to convert into syndiotactic active sites during the polymerization, which led to the formation of a syndiotactic block.