Synthesis and Characterization of Multi-block Polymers Consisting of Polyethylene/Ethylene-propylene Random Copolymer via [N,P]-type Non-metallocene Catalysts

Eight [N,P]-type non-metallocene catalysts were synthesized successfully via the reaction between two kinds of ligands carrying different electronic effect groups and chloride compounds of transition metals Ti, Zr, Ni and Pd. Catalyst Cat. L2-Ti exhibited the highest catalytic activity toward ethylene/propylene copolymerization thanks to the combined effects exerted by ligand structure, central atomic species, and polymerization conditions on copolymerization behavior of ethylene with propylene. The copolymer product achieved a high M-w up to 2.75 x 10(5) g/mol as measured by GPC, and C-13-NMR test suggested that the content of propylene insertion within copolymer backbone reached 11.5 mol%. Characterization with C-13-NMR, DSC, and WAXD demonstrated that macromolecular chains of the obtained copolymer were composed mainly of ethylene units existing as long-chain segments, while some other ethylene units formed random segments with copolymerized propylene monomers. Melting point of the copolymer decreased along with the increasing amount of propylene insertion, and so did the peak intensity in crystal diffraction of polyethylene segments. At the greatest insertion amount of propylene of 11.5 mol%, the melting peak could hardly be noted on DSC curve, and the peak intensity in crystal diffraction weakened markedly as well. Moreover, neither the characteristic peak in FTIR spectra nor the diffraction peak on WAXD patterns showed up for the long segments of polypropylene. Together with the missing melting peak of isotactic polypropylene on DSC curve, it was inferred that polypropylene hardly existed in the long-chain form basically. All these results confirmed the effective role played by [N,P]-type non-metallocene catalysts in the preparation of multi-block copolymers PE-b-P(E/P).