Propene polymerization with MgCl2-supported catalysts: Effects of using a diether as external donor

C-13 NMR analysis of poly(propylene) fractions of different tacticity, obtained using a catalyst system of type MgCl2/TiCl4/diisobutyl phthalate - AlEt3 - diether, has provided further evidence that the active species in this system are similar to those in which the ether is used as ''internal'' rather than ''external'' donor. Chain-end analysis of relatively low molecular weight polymer fractions indicated, for polymers of similar molecular weight, similar proportions of butyl-terminated chain-ends, indicative of chain transfer with hydrogen following regioirregular (2,1-) insertion. The relatively high hydrogen response of diether-containing catalyst systems can therefore be largely ascribed to this phenomenon, irrespective of whether the diether is used as internal or external donor. At relatively low hydrogen concentrations, chain transfer to hydrogen takes place predominantly after the occasional secondary insertion, while the additional presence of vinylidene chain-ends in certain xylene-soluble fractions indicates that chain transfer via beta-H transfer takes place mainly after primary insertion.