Effect of catalyst isospecificity on olefin copolymerization

Copolymerizations of ethylene with propene, ethylene with 1‐hexene, and propene with 1‐hexene were performed at 40°C under atmospheric pressure by using the aspecific catalyst composed of TiCl3/MgCl2 and Al(C2H5)3 and the isospecific Solvay‐type catalyst composed of TiCl3 and Cp2Ti(CH3)2. In case of ethylene‐propene copolymerization, the catalyst isospecificity affects neither the monomer reactivity ratios nor the monomer distribution in poly(ethylene‐co‐propene). The thermal properties of poly(ethylene‐co‐propene) are, however, not the same for the two catalysts due to the different tacticity of long propylene sequences contained in the copolymers. In the copolymerizations of ethylene and 1‐hexene and of propene and 1‐hexene, the monomer reactivity ratios differ to some extent between the two catalyst systems. The aspecific catalyst facilitates incorporation of 1‐hexene both in poly(ethylene‐co‐1‐hexene) and poly(propene‐co‐1‐hexene). The monomer distributions are also different in these copolymers. The aspecific and isospecific catalysts show a tendency to give random and blocky copolymers, respectively.