Secondary syndiotactic-specific propene insertion in the presence of homogeneous V-based catalysts

This paper shows, by terminating the polymerization through deuterolysis wi th CF3CH2OD, that the propyl end groups of-syndiotactic polypropylene obtai ned in the presence of homogeneous catalysts,based on vanadium salts and al kylaluminium halides, such as VCl4-Al(C2H5)(2)Cl-Anysole, arise, at least m ostly, from termination, thus confirming the Coleman-Fox type of the statis tical model of the propagation already proposed in previous papers. Direct evidence is also provided that secondary insertion of propene is the only s yndiotactic specific polymerization step. In view of this, the early hypoth eses concerning the structure of the active species promoting syndiotactic specific polymerization are critically reconsidered. (C) 2000 Elsevier Scie nce B.V. All rights reserved.