REGIOSPECIFICITY AND STEREOSPECIFICITY IN PROPENE POLYMERIZATION WITHMGCL2-SUPPORTED ZIEGLER-NATTA CATALYSTS - EFFECTS OF HYDROGEN AND THEEXTERNAL DONOR

Investigation of the effects of hydrogen and different external donors on the stereoregularity and chain-end distribution of polypropylene p repared using MgCl2/TiCl4/phthalate ester-AlEt(3)-alkoxysilane catalys t systems has not only confirmed the importance of regiospecificity in relation to hydrogen activation but has also indicated a significant effect of stereospecificity. Alkoxysilanes giving high isospecificity also give high molecular weight polypropylene. Polymer stereoregularit y also increases with increasing hydrogen concentration in polymerizat ion. These effects indicate that not only regioirregular but also ster eoirregular insertion slows down chain propagation. In each case the p robability of chain transfer with hydrogen is higher than that followi ng a stereoregular insertion, and in each case chain transfer with hyd rogen leads to the regeneration of isospecific propagation.