The Investigation Of Living Radical Polymerization Of Styrene And Copolymerization Of Styrene With Ethylene Promoted By Metallocene Complexes

Linear and multi-arms atacticpolystyrene with functional group -OH was synthesized via living free radical polymerization promoted by metallocene complexes, in the presence of glycidyl-4-methoxyphenyl ether(I₁), 1,4-butanediol diglycidyl ether(I₂), 4,4'-Methylenebis(N,N-diglycidylaniline) (I₄) and Poly(phenylglycidyl ether)-co-Formaldehyde (I_S) as initiators, Sn as reducing agent in this catalyst system. The polymerization mechanism was expatiated. In this article, for the first time, titanocene complexes, for example CpTi (â…£)Cl₃ was treated with Sn to form primary free r2adical CpTi(â…¢)Cl₂ at room temperature, this radical reacted with epoxide(initiator) to give the chain radical which initiated styrene to propagate successfully. The effect of polymerization conditions, such as the structure of the initiator and metallocene complexes, as well as the ratio of initiator to monomers on the performance was investigated. The properties of the obtained polymer were also characterized by GPC. These results showed that the structure of initiator had little influence on the conversion of monomer, the molecular weight and molecular weight distribution of the obtained polymer. Compared with (n-BuCp)₂TiCl₂ and SiMe₂(Ind)₂TiCl₂, half-titanocene, CpTICl₃ was favorable for the polymerization of styrene via radical mechanism. The monomer conversion was more than 80%, the molecular weight of the polymer was higher than 1.0?0⁵ and the molecular weight distribution was at the range of 1.08 to 1.42. However, (n-BuCp)₂TiCl₂ and SiMe₂(Ind)₂TiCl₂ used as catalyst, the monomer conversion and the molecular weight of the obtained polymer were lower. But the structure of metallocene complex had less impact on the molecular weight distribution (1.26 - 1.30). The effect of the ratio of monomer to initiator on the polymerization performance was also studied. A linear dependence of Mn of the obtained polymer on the monomer conversion was observed at the ratio of 250/1, 500/1 and 750/1. Mn of the obtained polymer increased with increasing of the ratio of monomer to initiator, and the molecular weight distribution of the obtained polymer kept at the range of 1.0 to 1.40. The obtained polymer was also characterized by ¹³C NMR to confirm that the polymer featured atactic structure. These results indicated that the polymerization mechanism was living free radical behavior. The number of arms and hydroxyl groups in each polymer molecule were both about four, which suggests that they arise from the epoxy functional groups of the initiator.By one-pot technique the copolymerization of styrene with ethylene by CpTiCl₃/BDGE/Zn catalytic system to produce S-E block copolymers has been investigated in the present of methylaluminoxane(MAO) as cocatalyst via sequential monomer addition strategy, and as well the effect of temperature, time, ethylene pressure and the ratio of Al/Ti in mol on the polymerization performance was discussed. It could notice that the yield of the copolymer and the number average molecular weight of the copolymer increased with increasing of reaction temperature at the range from 30℃to 50℃. Whereas the molecular weight distribution (MWD) of the copolymer varied slightly at the range from 1.71 to 2.11. These results indicated that the catalytic active centre was stable at the temperature range from 30℃to 50℃and the propagation rate increased with increasing of temperature. However, the number average molecular weight of the copolymer decreased and MWD of the copolymer became broad as the polymerization temperature increased from 50 to 70℃, it was possible that the active species deactivated easily and the chain transfer reaction was enhanced as the temperature increased, and the concentration of ethylene in solvent decreased at higher temperature. Independently from the feed composition, basically S-E block copolymers are obtained, together with some polyethylene and syndiotacticpolystyrene, from which the former can be separated by solvent extraction. The CHCl₃-soluble product was determined by GPC, DSC, WAXD and ¹³C NMR. The DSC results show that the copolymers has a glass transition temperature (Tg = 86℃) and melting temperature (Tm=118℃) which is attributed to Tg of aPS chains and Tm of PE chains, respectively. The block structure of the aPS-b-PE copolymer is further confirmed by WAXD and ¹³C NMR.