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Gas Phase Polymerization Of Conjugated Dienes With Supported Rare Earth Catalyst: Kinetics And Molecular Weight Control

Posted on:2003-05-18Degree:MasterType:Thesis
Country:ChinaCandidate:J F LiFull Text:PDF
GTID:2121360062475847Subject:Polymer Chemistry and Physics
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It has been known that rare earth coordination catalysts are much effective for the polymerization of conjugated dienes, such as butadiene or isoprene. The obtained polymer has very high cis-l,4 structure content (>95%). For a long time the polymerization of butadiene or isoprene has been carried out in solution or bulk mode. These multi-step processes are energy and labor intensive and require many solvent separation steps. Additionally, such processes have a number of environmental concerns associated with them.In recent ~'ears, gas phase polymerization has been used successfully in the manufacture of polvolefxns. It has been proved that gas phase po]vmerizaton is a good means for polymerization with dramatic reduction in capital investment and energy usage, and can be minimizing environmental contents. Therefore gas phase polymerization causes a revolution in producing diene rubber. But up to now there are on] a few patents on this field and the activity of catalysts these patents mentioned are very low or the cis-content is not high enough.n this thesis. Si02 supported rare earth catalyst composed with Nd(naph)3-Al2Et3Cl3- Al(iBu)3 and/or Al(i-Bu).,H was prepared for the gas phase polymerization of butadiene with fairly high catalytic activit and cis-1.4 selectivity. The effects of Al/H molar ratio, Al/Nd molar ratio, reaction time, polymerization temperature on catalyst activity and molecular weight of polvbutadiene were studied. The results indicate the molecular weight of the polymers decreased significantly with increasing Al/Nd or A](i-Bu)2H ratio in co-catalyst, but polymerization conditions have little effect. Note that the molecular weight (Mw) of polvbutadiene by gas phase polymerization can be controlled in a wide range from 40>< l0~~-~ I00X 104g/mol by changing the molar ratio of Al/Nd or Al/H. We also find that Al/Nd, Al/H and reactor time have much effect on the molecular weight distribution (MWD) of polvbutadiene. When the catalyst system containing Al(i-Bu)3 and AIH(i-Bu)2. the MWD of polymers is broader than that onl using Al(i-Bu)3 or AIH(i-Bu)2 as co-catalyst, and the catalytic activity is higher also. This indicates there is interaction effect between Al(i-Bu)3 and A1H(i-Bu)2. It has been proved that two different sites are generated in Nd-basedIIIcatalyzed polymerization, one is fast but short lived center and the other is slow growing but stable. The formation of these two active sites is determined by co-catalyst component.Rare earth catalysts were also applied to the gas phase polymerization of isoprene, proceeding to give high cis-content. Experiments were performed with various rare earth elements and ligands. The catalytic activity sequence of rare earth elements and ligands is Nd"Gd>Er>Sm and naph>P507>acac> CF3COO-, respectively. The inferences of polymerization temperature, reaction time, catalyst concentration, the molar ratios between the components of catalysts were also discussed. As a result, the best conditions for gas phase polvmerzation of isoprene are AlINd=l00~-l20, CL'Nd=4~-5, A]IH=7/Y-6/4, 50C, with the high catalytic efficiency of about 1200 Kg PJP/mol Lwh after 1 hour and molecular weight (Mw) of the PIP obtained about 50 X 1 O4glmol.The kinetic behavior of gas phase polymerization of isoprene with Si02-[Nd(naph)3-Al-,Et3CJ3-Al(i-Bu)3/AIH(i-Bu)2] catalyst system was studied. The reaction rate increases significantly and reaches a maximum values after 5- 10 minutes, then decreases slowly.The same supported catalyst systems. Si02-[Nd(naph)3-A12Et3C13-Al(i-Bu)3/A1H(i-Bu)2]. has been also firstly uti]ized in the gas phase copolymenzation of butadiene and isoprene. Copolymer was obtained by feeding butadiene and polymerizing for certain time, after vacuumed, isoprene was feeded and polymerizied for certain time. The copolymer was proved to be block-copolymer by DSC and GPC analysis. JR spectrum indicates the block copolymer with high cis-content of both polybutadiene and polvsoprene unit, which particular microstructu...
Keywords/Search Tags:supported rare earth catalyst, butadiene, isoprene, gas phase polymerization, block copplymerization, molecular weight controlled, kinetics
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