HYDROGEN ACTIVATION IN PROPENE POLYMERIZATION WITH MGCL2-SUPPORTED ZIEGLER-NATTA CATALYSTS - THE EFFECT OF THE EXTERNAL DONOR

C-13 NMR analysis of relatively low-molecular-weight polypropylenes pr epared using the catalyst system MgCl2/TiCl4/phthalate ester-AlEt3-ext ernal Lewis base has revealed the presence of up to around 20% butyl ( n-Bu) chain ends, indicative of regioirregular (2,1-) monomer insertio n followed by chain transfer with hydrogen. The effect of hydrogen on catalyst activity depends on the nature of the external donor, and the results indicate that at least part of the observed increase in catal yst activity in the presence of hydrogen can be ascribed to the regene ration of active species via chain transfer at dormant (2,1-inserted) sites.