The In Situ Copolymerization Of Ethylene To Prepare High Performance LLDPE

Ethylene in situ copolymerization is a way of producing LLDPE with ethylene as the sole monomer by combining of ethylene oligmerization and copolymerization catalysts. At present, the oligmerization catalysts employed in in situ copolymerization catalytic systems are ethylene dimerization catalysts, wide range ethylene oligomerization catalysts and ethylene trimerization catalysts. However, the properties of the LLDPE which is produce by 1-octene as the comonomer is better than the LLDPE produced by 1-butylene and 1-hexene as the comonomers. In this thesis, the PNP/Cr(Ⅲ) ethylene tetramerization catalyst was employed as oligmerization catalyst and metallocene catalyst was employed as copolymerization catalyst to produce hexyl-branched high performance LLDPE.The thesis was composed in two parts: (1) the performance of the catalyst for tetramerization of ethylene; (2) the in situ copolymerization of ethylene to produce hexyl-branched LLDPE by ethylene tetramerization catalyst and metallocene catalyst.In the first part, the highly selective bis(diphenylphosphino)cyclopentylamine ligand for the synthesis of 1-octene was synthesized. Cr(acac)3 was employed as main catalyst, MAO was employed as cocatalyst and carbon tetrachloride was employed as accelerant. We have researched the effects of molar ratio of ligand and main catalyst, reaction temperature, reaction pressure and cocatalyst amount on ethylene tetramerization activity and 1-octene selectivity.In the second part, we have researched the effects of molar ratio of tetramerization catalyst and metallocene catalyst, reaction temperature, and cocatalyst amount on the activity of in situ copolymerization and the properties of productions. The results show that the obvious positive comonomer effect was exist in in situ copolymerization catalytic system. The thermal stability of in situ copolymerization catalytic system is better than ethylene polymerization catalyst. With the increase of temperature from 30℃to 80℃, the activity is increased. The amount of cocatalyst affect the properties of productions largely. When the amount of cocatalyst is increased, the molecular weights of copolymers are decreased. The melt points and densities of productions are also decreased with the increase of the amount of cocatalyst. 13C-NMR was used to determine the composition and chain structure of the copolymers. The results show that the obtained copolymers are branched PE. The amount of hexyl is largest in all branched chains. The proportion is 64.97%. There are also exist some butyl (27.39%) and a few ethyl (7.64%).