Single-site polymerization catalysts: branched polyethylene and syndiotactic poly(alpha-olefins)

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Title: Single-site polymerization catalysts: branched polyethylene and syndiotactic poly(alpha-olefins)
Author: Schwerdtfeger, Eric Dean
Abstract: Utilization of methylaluminoxane (MAO ) activated metallocene and constrained geometry (CGC ) olefin polymerization catalysts containing fluorenyl or octamethyloctahydrodibenzofluorenyl (Oct ) moieties has yielded three series of syndiotactic copolymers of propylene with higher a -olefins . The melting temperatures of these polymers were analyzed , and found to correspond directly with the mole percent incorporation of comonomer , as well as with the frequency of stereoerrors in the polymers . Further analysis indicated that rmrr stereoerrors , a result of site epimerization , occur in close proximity to the incorporated comonomers . The MAO -activated fluorenyl /Oct -containing metallocene and CGC catalysts were further utilized to produce syndiotactic samples of poly (1 -butene ) (s -PB ) and poly (1 - pentene ) (s -PPe ) . The syndiotacticity of the samples was quantified by 13C NMR and the melting temperatures determined by DSC . The samples of s -PB and s -PPe produced by Me2Si ( h1 -C29H36 ) ( h1 -N -tBu )ZrCl2 ?OEt2 (Oct -CGC ) were found to melt at higher temperatures (55 .9 and 43 .1 ?C , respectively ) than any previously reported samples . The MAO -activated Oct -CGC was also used to produce polyethylene samples at a variety of polymerization temperatures and pressures . All of the samples were found to contain an unprecedented degree of branching (13 -65 total branches per 1000 carbon atoms ) for an early transition metal single -site catalyst . The branches were found to be almost exclusively of two or greater than five carbon atoms in length , and the levels of the longer branches could be controlled by varying the polymerization conditions . The number of ethyl branches was roughly 5 per 1000 carbon atoms for all samples . Finally , a binary catalyst system comprising the Oct -CGC and a chromium -based ethylene trimerization catalyst , ( (tBuSCH2CH2 )2NH )CrCl3 , was developed . This MAOactivated catalyst system could be tuned to produce polyethylene samples with 17 -49 total branches per 1000 carbon atoms . Between 4 and 16 of these branches were found to arise from incorporation of 1 -hexene produced by the chromium oligomerization catalyst . Adjusting the ratios of oligomerization catalyst , polymerization catalyst , and activator was found to allow rational control over the branch content of the polymers . The branching levels could also be varied by altering the time between injection of the oligomerization and polymerization catalysts into the system .
URI: http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2453
Date: 2009-05-15


Single-site polymerization catalysts: branched polyethylene and syndiotactic poly(alpha-olefins). Available electronically from http : / /hdl .handle .net /1969 .1 /ETD -TAMU -2453 .

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