A theoretical study of the competition between ethylene insertion and chain transfer in cationic aluminum systems

The ability of density functional models in dealing with polymerization mec hanisms has been investigated by comparison with high level post-Hartree-Fo ck methods. Ethylene insertion and chain transfer reactions have been compa red for a model of the active species suggested for the Jordan aluminum cat alyst [{R'C(NR")(2))}AIR](+). Conventional density functional approaches (B P86) show a strong bias in favor of chain transfer reactions via hydrogen t ransfer. The B1LYP model provides improved energy barriers. The aluminum mo del used strongly favors chain transfer over insertion, this preference bei ng further enhanced by lengthening the growing polymer chain. These finding s cast some doubts about currently accepted models of the active species in the Jordan catalyst. (C) 2000 Elsevier Science B.V. All rights reserved.