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Synthesis Of High Cis-1,4Polydienes With Narrow Molecular Weight Distribution Using Nd-based Catalyst Systems

Posted on:2014-01-21Degree:MasterType:Thesis
Country:ChinaCandidate:X G LiuFull Text:PDF
GTID:2231330395998819Subject:Polymer materials
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Catalytic systems based on lanthanides especially neodymium (Nd) have attracted a great deal of attention for the polymerization of conjugated dienes in both academia and industry due to their high catalytic activity and high cis-1,4selectivity. The resultant polydienes show excellent properties which are suitable to the use as tires and other elastic materials.In particular, Nd-based polydienes with a narrow molecular weight distribution (MWD) is desirable for high abrasion resistance, low heat build-up and high tensile properties. In this study, three Nd-based catalysts were examined in the polymerization of1,3-dienes (butadiene and isoprene). These catalysts displayed high activity and cis-1,4selectivity, giving polybutadiene and polyisoprene with high cis-1,4content, high molecular weight, and relatively narrow MWD. The effects of [Al]/[Nd](or [Li]/[Nd]),[Bd]/[Nd] and [Cl]/[Nd] ratios, alkylaluminum type, polymerization temperature and solvents on1,3-diene polymerization were investigated in detail, the results are as follows:(1) Butadiene polymerization with Nd(vers)3/HAl(i-Bu)2/AlEt2Cl catalyst. Polybutadienes with high cis-1,4content of98.3%and narrow MWD of1.47were prepared at50℃using catalyst aged at60℃for2h at [Bd]/[Nd]=50,[Al]/[Nd]=10, and [Cl]/[Nd]=3.0, respectively. The increment of butadiene addition amount in catalyst preparation resulted in the higher catalytic activity and narrower molecular weight distribution of the polymer. As the polymerization temperature increasing, higher catalysts activities, decreasing of Mn, and broader MWD (still less than2.2) were observed. Regardless of reaction conditions, the micro structure of the polymer hardly changed, indicating the high stability of the formed active species.(2) Butadiene polymerization with Nd(vers)3/n-BuLi/AlEt2Cl catalyst. Nd(vers)3/n-BuLi/AlEt2Cl catalyst exhibited high activity and cis-1,4selectivity towards butadiene polymerization. The highest catalyst activity were obtained at [Li]/[Nd]=12and [Al]/[Nd]=15, the polymer yield reached99.5%at30℃for4h in cyclohexane. The polymer produced at low temperature of0℃had high cis-1,4content of97.6%and narrow molecular weight distribution of1.23. The increment of polymerization temperature led to the increased catalyst activity and the decreased molecular weight ranging from112.3×104to28.0x104and cis-1,4content ranging from97.6%to88.9%of the polymer.(3) Isoprene polymerization with NdCl3-xTBP/MAO (x=3,4and6) catalyst. NdC13·3TBP activated by MAO worked effectively for isoprene polymerization. The polymer yield was up to97%at [Al]/[Nd]=100. The produced polymer features high cis-1,4stereoregularity, high molecular weight and narrow MWD. Compared to HA1(i-Bu)2and Al(i-Bu)3systems, MAO-based catalyst afforded polymer with higher molecular weight, narrower MWD, and higher cis-1,4content. The activity of catalyst increases with the polymerization temperature increasing, and the cis-1,4content decrease slightly ranging from98.1%(0℃) to96.2%(50℃).
Keywords/Search Tags:Rare earth catalyst, Polymerization, Polybutadiene, Polyisoprene
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