Reference

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz carbon-13 n

Studies of the stereospecific polymerization mechanism of propylene by a modified Ziegler-Natta catalyst based on 125 MHz carbon-13 n.m.r. spectra. Inoue, Yoshio; Itabashi, Yuichi; Chujo, Riichiro; Doi, Yoshiharu (Dep. Polym. Chem., Tokyo Inst. Technol., Tokyo 152, Japan). Polymer, 25(11), 1640-4 (English) 1984. CODEN: POLMAG. ISSN: 0032-3861. DOCUMENT TYPE: Journal CA Section: 35 (Chemistry of Synthetic High Polymers) The mechanism of stereospecific polymn. of propylene [115-07-1] (catalyzed by a modified Ziegler-Natta system, TiCl4-MgCl2-C6H5COOC2H5 [93-89-0]-Al(C2H5)3 [97-93-8]), has been analyzed using the values of triad and pentad tacticity detd. using 125 MHz 13C NMR spectroscopy. The well-known single active-site models, such as the Bernoullian, first- and second-Markovian, and enantiomorphic models, were found to be inadequate to describe the obsd. tacticity. A two-sites model, in which at one site the stereospecific polymn. proceeds by means of a Bernoullian model and at the other by an enantiomorphic-site model, is proposed. It was found that the pentad tacticities of both sol. and insol. (in boiling heptane) fractions of polypropylene agreed well with the two-sites model.

Transition metal alkyl polymerization - progress and development

Transition metal alkyl polymerization - progress and development. Tait, Peter J. T.; Eid, Maher Abu (Dep. Chem., UMIST, Manchester M6O 1QD, UK). Actas Simp. Iberoam. Catal., 9th, Volume 1, 163-82. Soc. Iberoam. Catal.: Lisbon, Port. (English) 1984. CODEN: 52TUAU. DOCUMENT TYPE: Conference CA Section: 35 (Chemistry of Synthetic High Polymers) Transition metal catalysts for the polymn. of ethylene and a-olefins were reviewed, and recent kinetic and active center concn. detns. were reported for the polymn. of 4-methyl-1-pentene [691-37-2] by catalysts of the type d-TiCl3.0.33AlCl3-Al(iso-Bu)3 [100-99-2] and supported catalysts of the type MgCl2-Et benzoate [93-89-0]-TiCl4-Al(iso-Bu)3. Variables studied included aluminum alkyl concn., Et benzoate concn., and milling time. The much higher activities obtained with MgCl2-supported catalysts were attributed to increases in the concn. of active centers and in the propagation rate.