V. Busico, R. Cipullo, Carmen Polzone
Mar 20, 2003
Citations
0
Influential Citations
54
Citations
Journal
Macromolecules
Abstract
The propene/ethene-[1-13C] copolymerization method has been applied to measure precisely the regioselectivity in propene polymerization of the “simple” MgCl2/TiCl4 catalyst (activated with Al(iBu)3), which can be viewed as the ancestor of all present-day MgCl2-supported industrial catalysts containing Lewis bases as selective modifiers. It has been found that the average content of 2,1-regiomistakes in the polypropylene produced is fairly high (ca. 0.7 mol %), althoughnot unexpectedly, due to the multisite catalyst naturethese are distributed rather nonuniformly throughout the polymer. The difficulty in detecting the 2,1-units, despite their relatively high concentration, in the 13C NMR spectra of homopolymer samples at natural 13C abundance has been traced to their occurrence in a variety of stereochemical environments, which leads to splitting and broadening of the corresponding resonances. The fraction of “dormant” polypropylene chains with a 2,1-last-inserted unit was estimated to be in the 20−50% ran...