Copolymerization of ethylene and in situ-generated α-olefins to high-performance linear low-density polyethylene with a two-catalyst system supported on mesoporous molecular sieves

摘要

The manufacture of linear low-density polyethylene (LLDPE) is of great significance in academia and industry. The employment of a single monomer, i.e. ethylene, to produce LLDPE by introducing two catalysts into one reactor to conduct ethylene copolymerization with in situ-generated α-olefins has proved to be an effective way in this case. Moreover, immobilization of catalysts affords LLDPE with better morphology and improved physical properties. An iron-based diimine complex immobilized on methylaluminoxane (MAO)-treated mesoporous molecular sieves was used to oligomerize ethylene to α-olefins with improved selectivity to lower molar mass fractions. Based on this, zirconocene compound was also supported on mesoporous molecular sieves to comprise a two-catalyst system to produce LLDPE from a single ethylene monomer. Copolymerization performed at both atmospheric and high pressure produced LLDPE of high molecular weight and broad molecular weight distribution without using MAO during the polymerization processes. Physical and mechanical measurements evidenced significant increases in tensile strength, tensile modulus and Izod impact strength. A marked shear-thinning phenomenon and improved storage modulus of LLDPE produced using catalysts supported on MCM-41 and SBA-15 mesoporous molecular sieves indicated a stronger interfacial interaction between the molecular sieve support and the polymeric matrix.