Homo- and Copolymerization of 4-Methyl-1-pentene and 1-Hexene with Pyridylamido Hafnium Catalyst

As a new generation of olefin polymerization catalyst, pyridylamido hafnium catalysts have unique ligand-modified activation mechanism and high isoselectivity for alpha-olefins polymerization. In this study, polymerizations of 4-methyl-1-pentene (4MP) and 1-hexene (Hex) catalyzed by classic pyridylamido hafnium catalyst were investigated, especially for the copolymerizations of 4MP and Hex. The pyridylamido hafnium catalyst showed high activity toward homo- and copolymerizations of 4MP and Hex. Isoselective homopolymerization of 4MP afforded narrowly polydispersed poly(4-methyl-1-pentene) (PMP) with high melting temperature up to 239 degrees C, while homopolymerization of Hex produced amorphous poly(1-hexene) with a bimodal distribution. Random copolymers of 4MP and Hex with different compositions were synthesized by adjusting the feed ratio of monomers. With decreasing feeding ratio of 4MP/Hex, monomer conversion and copolymerizataion activity increased because the hex-inserted hafnium active species was more active than the 4MP-inserted hafnium active species. Besides, decreasing feeding ratio of 4MP/Hex also led to a decrease in molecular weight and melting temperature of copolymer but caused a broadening in molecular weight distribution. H-1- and C-13-NMR spectrocopies clearly proved the resultant random copolymers were highly isotactic ([mmmm]>99%). The analysis results of differential scanning calorimetry (DSC), and wide-angle X-ray diffraction (WAXD) of polymers showed that the insertion of Hex unit into PMP changed its melting temperature and crystallization property.