| The copolymers of ethylene with 1-butylene,1-hexene and 1-octene are important polymer materials. Introduction of longer a-olefins to the polyethylene chain leads to decreased chain regularity, and in consequence to lower crystallinity, melting temperature and density, which improve the properties of the polyolefins obtained in application area. In fact, the properties of the copolymers which are produced by 1-octene and 1-hexene as comonomers are better than the copolymer produced by 1-butylene as comonomer. Basing upon the opinions mentioned forgoing, in this thesis, we report that the modified supported Ziegler-Natta catalysts, that prepare by two methods, are for the copolymerization of ethylene with longer a-olefins(1-hexene and 1-octene) to obtain high performance ethylene copolymers.The thesis is composed in two parts:The investigation of ethylene/1-octene copolymerization catalyzed by (iso-PentylO)TiCl3 /MgCl2/Et3Al (Ⅱ) and (BzO)TiCl3/MgCl2/Et3Al (Ⅲ) and ethylene/ 1-hexene copolymer catalyzed by TiCl4/ROH/MgCl2/Et3Al. In the first part, the two modified supported Ziegler-Natta catalysts (iso-PentylO)TiCl3/MgCl2/Et3Al (Ⅱ) and (BzO)TiCl3/MgCl2/Et3Al (Ⅲ) are employed in study on ethylene/1-octene copolymerization. The structure and properties of ethylene/1-octene copolymer obtained are characterized with 13C NMR, WAXD and DSC. The influences of the ligand structure of the catalyst, Al/Ti molar ratio, temperature and ethylene/1-octene feeding molar ratio on the catalytic activity, molecular weight of the copolymer obtained, comonomer incorporation and the copolymer microstructure have been discussed in detail. It is found that the incorporation of 1-octene in the polymer increased with the increasing of the concentration of the comonomer in the feed. Comparison with the traditional supported Ziegler-Natta system for ethylene/1-ocene copolymerization with comonomer incorporation of 0.34%, the comonomer incorporation in the copolymers synthesized by the modified supported Ziegler-Natta systems (iso-PentylO)TiCl3/MgCl2/Et3Al (Ⅱ) and (BzO)TiCl3/MgCl2/Et3Al (Ⅲ) show an improved copolymerization activity and an enhanced comonomer incorporation up to 2.26 mol% and 7.46 mol%, respectively. Based on the 13C NMR result, the comonomer reactivity ratios are calculated, respectively, rE=55.00 for ethylene and rO =0.023 for 1-octene with rE·rO=1.27 for (iso-PentylO)TiCl3/MgCl2 (Ⅱ) catalyst; rE=17.15 for ethylene and rO=0.055 for 1-octene with rE·rO= 0.93 for (BzO)TiCl3/MgCl2(Ⅲ) catalyst. The value of rE·rO are close to 1, reflecting a pronounced tendency for the random distribution of the comonomers in the copolymer chain.In the second part, the synthesis of copolymer featured high comonomer incorporation and broaden molecular weight distribution from ethylene with 1-hexene catalyzed by TiCl4/ROH/MgCl2, AlEt3 used as co-catalyst, is described. The influences of the catalyst system composition and the polymerization conditions on the behavior of ethylene/1-hexene copolymerization, and the structure, molecular weight and molecular weight distribution of the copolymers obtained have been discussed in detail. The copolymerization is performed under the optimum conditions:n (Ti)/n(Mg) of 10/1, n (ROH)/n (MgCl2) of 1.5/1, n (Al)/n (Ti) of 100/1, ethylene pressure of 0.12 MPa, polymerization temperature of 70℃, polymerization time of 1 h and the comonomer concentration in feed of 0.25mol/L, the catalytic activity reaches 0.76 Kg/g cat.h. The catalyst particle shape and the structure and properties of the ethylene/1-octene copolymer obtained are characterized with 13C NMR, SEM, WAXD, DSC and GPC. These results show that the catalytic activity, molecular weight distribution and higher 1-hexene incorporation are considerably improved when 1-octanol (ROH) adds into the catalyst system. Adding ROH in the catalyst system, Ti concentration of the catalyst is increased, up to 4.8 wt%; the MWD of the copolymer becomes broader, ranging at 15 to 20; 1-hexene incorporation within the copolymer chain is higher, up to 2.6 mol%.
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