Modification of polyethylene by sequential homo- and copolymerization of ethylene and alpha-olefins over homogeneous zirconocene catalysts

Ethylene was sequentially homopolymerized (35°C, 15-90 min) and copolymerized (35°C, 25-30 min) with 1-hexene or 1-octene over a Cp2ZrCl2/MAO or a C2H4(Ind)2ZrCl2/MAO catalyst in toluene as solvent; a-olefin conversions were 55-60 mol %. The preliminary homopolymeriza-tion of ethylene was found to affect only slightly the composition and the MW and MWD property data of the resulting ethylene-hexene (CEH) and ethylene-octene (CEO) copolymers. HDPE/CEH and HDPE/CEO reactor mixtures (RM) were synthesized, containing various proportions of the copolymers (Table 2). The RM components were found to cocrystallize during the polymerization process. Mechanical property data were determined for pure and for modified HDPE (Table 3). With the copolymer endowed with desired properties and introduced into HDPE in an appropriate amount, high-strength and simultaneously high-MFR materials can be prepared.