Study On The Copolymerization Of Styrene And Isoprene Catalyzed By Supported Ziegler-Natta Catalyst

In olefin catalysis and polymerization,the supported Ziegler-Natta catalyst is one the most important industry catalyst.It is widely used in the polymerization of?-olefin such as propylene and ethylene and conjugated diolefin such as isoprene and butadiene due to its high polymerization activity and high steric selectivity and low preparation cost.In this paper,the supported Ziegler-Natta catalyst[TiCl₄/Mg Cl₂-Al(i-Bu)₃]was used for the stereospecific copolymerization of styrene and isoprene.The effects of Al/Ti,tp and Ip/St on polymerization activity,catalyst efficiency,product composition and copolymer structure were investigated.The product was fractionated by solvent extraction method,and the molecular chain structure of the product was characterized by NMR,GPC,DSC and FT-IR.Based on the analysis of the copolymerization behavior and St-Ip copolymer structure,the mechanism of the stereospecific copolymerization?-olefin and conjugated diolefin by supported Ziegler-Natta catalyst were explored.A series of St-Ip copolymers with different styrene content were obtained by changing Ip/St with other conditions unchanged.The glass transition temperature(T_g),melting temperature(T_m)and melting enthalpy(?H_m)of the copolymer were observed by DSC.The copolymer structure was qualitatively analyzed by FT-IR.The structure and chain length of the copolymer were quantitatively analyzed by ¹H-NMR and ¹³C-NMR.The Mw and Mw/Mn of copolymer were observed by GPC.The results showed that the copolymer was a copolymer containing two T_g,in which the polyisoprene chain segment was highly trans-1,4-structure and the polystyrene chain segment was isotactic structure.With the increase of the amount of styrene monomer,the amount of styrene inserted into the copolymer increased,the length of styrene chain increased,the Mw/Mn of the copolymer increased,while the crystallization property decreased obviously.The effects of Al/Ti and tp on the copolymerization activity and copolymer structure were studied under the condition of fixed Ip/St.The results showed that the conversion rate,catalytic activity and styrene insertion amount reached the highest when Al/Ti was about 100 mol/mol.The conversion rate and catalytic activity decreased with tp have raised,but the amount of inserted styrene increase.And the optimum temperature of the copolymerization was 50?.According to the K-T method the monomer reaction rates were calculated(r _St=0.14and r _Ip=11.12),which indicated that the copolymerization was non-ideal copolymerization without azeotropic point,that is,the copolymer structure changed with the reaction time obviously.The copolymers with different chain structures were separated by n-hexane solvent extraction method,and the microscopic chain structures of the soluble and insoluble substances were characterized by DSC,¹H-NMR and ¹³C-NMR,and the following conclusions were drawn:The solubility of copolymer in n-hexane was related to the length of TPI and PS chain.The n-hexane soluble is the copolymer with long TPI chain and short PS chain.The insoluble is a copolymer with long i PS and short TPI chains.The chloride quenching method was used to obtain the[C^*]/[Ti]value,and the multiple Flory most probable distribution function fitting method was used to analyze the catalytic active center distribution,the XPS was used to determine the valence state of Ti.According to the results,some conclusions can be obtained.The active species catalyzed the St-Ip copolymerization was Ti³⁺.The copolymerization has two kinds active sites:C^*-2 with low steric hindrance and C^*-1 with high steric hindrance.C^*-1could obtain high trans-1,4-PI and i PS.Based on the results,the copolymerization mechanism of styrene and isoprene catalyzed by TiCl₄/Mg Cl₂-Al(i-Bu)₃ was speculated.