The Hydrogen Effect on the Molecular Structure of Polyolefins, Produced over Supported TiCl4/MgCl2 Catalysts
Hydrogen is the most effective chain transfer agent, which is widely used to reduce molecular weight of polyolefins (polyethylene (PE), polypropylene (PP)) produced over Ziegler-Natta catalysts, especially over TiC4/MgCl2-supported catalysts (TMC). The activity of catalysts changes also with introduction of the hydrogen to the polymerization: activity decreases in ethylene polymerization1-5 and increases in propylene6-8 and hexene-19 polymerization.
Present work contains the data on the hydrogen effect on the molecular weight and molecular weight distribution of PE, PP, polyhexene (PH) and ethylene/propylene (EPC), ethylene/hexene copolymers (EHC), produced over TMC of different composition.
Introduction of hydrogen results in considerable decrease in the MW of all polyolefins under study (Figure 1). The molecular weight distribution (the Mw/Mn ratio) does not change in the case of polyethylene and narrows for polypropylene, polyhexene and copolymers of ethylene with α-olefins. The possible reasons of such phenomenon were discussed.