Ethylene/1-hexene Copolymers Made By Tandem Polymerization Of Ethylene Using A Trimerization Catalyst Feeding Policy

Polyolefin is one of the largest classes of thermoplastics with a wide range of applications.Its technical level is often reflective of the level of science and technology in a country.Tandem catalyst system has been used to produce ethylene/a-olefin copolymer in the reactor with ethylene as the only monomer.Therefore,it eliminates the need for the production,purification,storage,and transportation of a-olefin as the second monomer,thus reducing the overall production cost.However,the copolymer produced by this system has a wide composition distribution.Polymer with high comonomer content generally possesses low melting point,which affects its thermal performance.The realization of polyolefin elastomers(POE)by ethylene tandem catalyst polymerization under high temperature and high pressure is currently not available.Control over chain structure and aggregation structure of copolymer have been demonstrated by using various monomer feeding policies in other polymerization systems.Therefore,we combined the use of feeding policy of oligomerization catalyst with ethylene tandem catalyst system to prepare ethylene/1-hexene copolymer with controlled distribution of copolymer composition,thus granting the copolymer with high melting point and low glass transition temperature.In this study,SNS-Cr was chosen as the oligomerization catalyst,CGC-Ti as the copolymerization catalyst,and MAO as the cocatalyst.Polymerization that uses the combination of these catalysts are referred here as the tandem catalyst system.The influence of polymerization pressure,temperature,and oligomerization catalyst feeding policy on the resulting copolymer composition,rheological properties,and mechanical properties are methodically investigated.We found oligomerization catalyst possesses the highest reactivity at 75? and can produce copolymer with high 1-hexene content.Under the same amount of oligomerization catalyst,increasing thefeeding times of oligomerization catalyst can improve the molecular weight of copolymer.At 75?,improvement over the thermal properties was also observed as evidenced by the higher melting point of the copolymer from oligomerization catalyst multiple feeding policy.The copolymers prepared by the tandem catalyst system under high temperature an pressure possessed 9.59-12.0 mol%of 1-hexene repeating units.This copolymers exhibited better fracture strength,elongation at break but worse elastic recovery performance compared to the commercial POE.The innovation of this study can be summarized as follows:1)We combined the feeding policy of oligomerization catalyst with ethylene tandem catalyst system,and prepared the ethylene/1-hexene copolymers.The copolymers maintain the elasticity and improve the melting point,elastic modulus,fracture strength.2)The ethylene/1-hexene copolymers with 1-hexene of 9.59-12.0 mol%were prepared by ethylene tandem catalyst system under high temperature and pressure.Compared with the commercial POE,the copolymers have better tensile properties but worse elastic recovery performance.