Cocatalyst On The Copolymerization Of Ethylene And Styrene

In the past decade, great interest has been devoted to the synthesis of well-defined ethylene-styrene copolymers. Depending on the polymerization conditions and the catalysts, random, alternating, block, and pseudorandom ethylene-styrene copolymers have been synthesized.The copolymerization of ethylene and styrene has been performed using supported N catalyst activated with Et2AlOAlEt2 and AlEt3 at the presence of diphenyldimethoxysilane(DDS). Especially, we study the influence of cocatalysts on the copolymerization of ethylene and styrene. The optimum copolymerization conditions of Al/Ti ratios, styrene concentrations and Si/Ti ratios were investigated. Copolymerization products were fractionated by successive solvents extraction with boiling methyl ethyl ketone (MEK) and boiling tetrahydrofuran (THF). The experimental results indicated copolymerization products include atactic Polystyrene(aPS), ethylene-styrene copolymer, and polyethylene(PE). Based on the experiments, we have made the following conclusions.When Al/Ti ratio varied between 50 and 400,the Et2AlOAlEt2 catalyst system exhibit an increase polymerization activity with the increase of Al/Ti ratio followed by a small decrease. For AlEt3 catalyst system, the catalytic activity has no obvious change. With the increase of Al/Ti ratio, the amount of aPS fraction of the product prepared by Et2AlOAlEt2 catalyst system will decrease, PE will increase and ethylene-styrene copolymer also will decrease. For AlEt3 catalyst system, the change of amount of aPS and PE fraction exhibit the same rules, but ethylene-styrene copolymers have no significant change.The ethylene-styrene copolymers were characterized by 13C-NMR, DSC and GPC. The measurement of I3C-NMR indicate that copolymers have some S-S sequenc -es, that is to say, styrene block exist in ethylene-styrene copolymers. For Et2AlOAlEt2 catalyst system, we also found the styrene contents in ethylene-styrene copolymers will increase with the decrease of Al/Ti ratio, but AlEt3 catalyst system has no such variation. The results of DSC measurement indicate the distribution ofstyrene unit of copolymers prepared by Et2AlOAlEt2 is homogeneous, leading to a single melting point (Tm). However, the heterogeneous distribution of styrene unit in copolymer generated by AlEt3 catalyst system results two close melting points. GPC curves of some copolymer produced by Et2AlOAlEt2 show an inverse peak in addition to a normal positive peak, which could be attributed to the intermolecular heterogeneity. The copolymer with low molecular weight contains low amount of styrene unit, while copolymer with high molecular weight contains high amount of styrene unit.The feed ratio of styrene also affects the composition, monomer distribution and molecule weight of the copolymer together with catalytic activity of the copolymerization.It is concluded that cocatalyst not only affects copolymerization activity of N-catalyst, but also influences the ratio of different fractions in copolymerization products, especially, the melting point and the glass transition temperature of ethylene-styrene copolymers in the presence of DDS.