Financial support was provided by the University of Minnesota (start up funds) and the ACS Petroleum Research Fund (54225-DNI3). Equipment purchases for the Chemistry Department NMR facility were supported through a grant from the NIH (S10OD011952) with matching funds from the University of Minnesota. We acknowledge the Minnesota NMR Center for high-temperature NMR. Funding for NMR instrumentation was provided by the Office of the Vice President for Research, the Medical School, the College of Biological Science, NIH, NSF, and the Minnesota Medical Foundation. We thank John Walzer (ExxonMobil) for a gift of PEEK high-throughput stirring paddles.

Caution: Please consult all relevant material safety data sheets (MSDS) before use. Several of the chemicals used in these syntheses are acutely toxic and carcinogenic, while several are pyrophoric and ignite in air. Please use all appropriate safety practices when performing these reactions including the use of engineering controls (fume hood, glovebox) and personal protective equipment (safety glasses, gloves, lab coat, full length pants, closed-toe shoes). Portions of the following procedures involve standard air-free...

<ol>
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Rev. 100 (4), 1223-1252 (2000).</li><li>Resconi, L., Cavallo, L., Fait, A., Piemontesi, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Selectivity+in+Propene+Polymerization+with+Metallocene+Catalysts.">Selectivity in Propene Polymerization with Metallocene Catalysts.</a> Chem. Rev. 100 (4), 1253-1346 (2000).</li><li>Valente, A., Mortreux, A., Visseaux, M., Zinck, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Coordinative+Chain+Transfer+Polymerization.">Coordinative Chain Transfer Polymerization.</a> Chem. Rev. 113 (5), 3836-3857 (2013).</li><li>Sita, L. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ex+Uno+Plures+(&amp;#34;Out+of+One,+Many&amp;#34;):+New+Paradigms+for+Expanding+the+Range+of+Polyolefins+through+Reversible+Group+Transfers.">Ex Uno Plures (&amp;#34;Out of One, Many&amp;#34;): New Paradigms for Expanding the Range of Polyolefins through Reversible Group Transfers.</a> Angew. Chem., Int. Ed. 48 (14), 2464-2472 (2009).</li><li>Kempe, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=How+to+Polymerize+Ethylene+in+a+Highly+Controlled+Fashion?.">How to Polymerize Ethylene in a Highly Controlled Fashion?.</a> Chem. Eur. J. 13 (10), 2764-2773 (2007).</li><li>van Meurs, M., Britovsek, G. J. P., Gibson, V. C., Cohen, S. 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The authors declare no competing financial interest.

A methyl-substituted cationic [&#945;-diimine]NiBr2 ethylene polymerization catalyst activated with MAO was examined for its competency for ethylene chain transfer polymerizations. The reactions were monitored via gas uptake measurements to determine the rate and extent of polymerization and catalyst lifetime, and the molecular weight of the resultant polymers were determined via gel permeation chromatography (GPC). Initially, the nickel catalyst was tested over a range of et...

Polyolefins are an important class of industrial polymers with uses in thermoplastics and elastomers. Significant advances in the design of single-site catalysts for the production of polyolefins has led to the ability to tune molecular weight, polydispersity, and polymer microstructure, which leads to a wide range of potential applications.1-3 More recently, chain transfer and chain shuttling polymerizations have been developed to give an additional route to modify the properties of the polymer without having to modify the catalyst.4-6 This system employs a single-site transition metal catalyst and a chain transfer reagent (CTR), which is typically a main group metal alkyl. During this polymerization, the growing polymer chain is able to transfer from the catalyst to the CTR, where the polymer chain remains dormant until it is transferred back to the catalyst. Meanwhile, the alkyl group that was transferred to the catalyst can initiate another polymer chain. In a chain transfer polymerization, one catalyst can initiate a greater number of chains compared to a standard catalytic polymerization. The polymer chains are terminated with the chain transfer metal; therefore further end-group functionalization is possible. This system can be used to change the molecular weight and molecular weight distribution of polyolefins,7 to catalyze Aufbau-like alkyl chain growth on main group metals,8 and for the synthesis of specialty polymers involving multicatalyst systems, such as block copolymers.9,10
Chain transfer polymerizations have been observed most commonly with early transition metals (Hf, Zr) and alkylzinc or alkylaluminum reagents, although examples exist across the transition metal series.5,7,8,11-16 In typical early transition metal catalyst systems, chain transfer is fast, efficient and reversible leading to narrow molecular weight distributions. Chain transfer/shuttling has been observed in mid-to-late transition metals (e.g. Cr, Fe, Co and Ni) with group 2 and 12 metal alkyls, although the rates of transfer are highly variable compared to early metals.4,7,17-19 Two main factors are apparently necessary for efficient chain transfer: a good match of metal-carbon bond dissociation energies for the polymerization catalyst and chain transfer reagent, and an appropriate steric environment to promote bimolecular formation/breakage of alkyl-bridged bimetallic intermediates.20 In the case of late transition metals, if the catalyst does not contain enough steric bulk, beta-hydride (&#946;-H) elimination will be the dominant termination pathway and will generally out-compete chain transfer.
Herein we report on a study of bimetallic chain transfer from nickel to zinc in a bis(2,6-dimethylphenyl)-2,3-butanediimine-based catalyst system with diethylzinc (ZnEt2) through small-scale high-throughput reactions. Chain transfer will be identified by examining changes in the molecular weight (Mw) and dispersity index of the resulting polyethylene through gel-permeation chromatography analysis. Chain transfer will also be identified through 13C NMR analysis of the ratio of vinyl to saturated chain ends as a function of chain transfer agent concentration. An in-depth kinetic analysis of the rates of propagation and chain transfer will also be presented.

<table border="0" cellpadding="0" cellspacing="0" style="width:675px;" width="674">
	<tbody>
		<tr height="25">
			<td height="25" style="height:25px;width:209px;">Endeavor Pressure Reactor</td>
			<td style="width:119px;">Biotage</td>
			<td style="width:107px;">EDV-1N-L</td>
			<td style="width:240px;"></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Blade Impellers</td>
			<td>Biotage</td>
			<td>900543</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">Glass Liners</td>
			<td>Biotage</td>
			<td>900676</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">2,3-butanedione, 99%</td>
			<td>Alfa Aesar</td>
			<td>A14217</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">2,6-dimethylaniline, 99%</td>
			<td>Sigma Aldrich</td>
			<td>D146005</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">formic acid, 95%</td>
			<td>Sigma Aldrich</td>
			<td>F0507</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">methanol, 99.8%</td>
			<td>Sigma Aldrich</td>
			<td>179337</td>
			<td>ACS Reagent</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">nickel (II) bromide, 99%</td>
			<td>Strem</td>
			<td>28-1140</td>
			<td>anhydrous, hygroscopic</td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">triethylorthoformate, 98%</td>
			<td>Sigma Aldrich</td>
			<td>304050</td>
			<td>dried with K2CO3 and distilled</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">1,2-dimethoxyethane, 99.5%</td>
			<td>Sigma Aldrich</td>
			<td>259527</td>
			<td>dried with Na/Benzophenone and distilled</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">pentane, 99%</td>
			<td>Fisher</td>
			<td>P399</td>
			<td>HPLC Grade *</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">dichloromethane, 99.5%</td>
			<td>Fisher</td>
			<td>D37</td>
			<td>ACS Reagent *</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">toluene, 99.8%</td>
			<td>Fisher</td>
			<td>T290</td>
			<td>HPLC Grade *</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">methylaluminoxane</td>
			<td>Albemarle</td>
			<td>MAO</td>
			<td>pyrophoric, 30% in toluene</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">diethylzinc, 95%</td>
			<td>Strem</td>
			<td>93-3030</td>
			<td>pyrophoric</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;">1,2,4-trichlorobenzene, 99%</td>
			<td>Sigma Aldrich</td>
			<td>296104</td>
			<td></td>
		</tr>
		<tr height="26">
			<td height="26" style="height:26px;">1,1,2,2-tetrachloroethane-D2, 99.6%</td>
			<td>Cambridge Isotopes</td>
			<td>DLM-35</td>
			<td></td>
		</tr>
	</tbody>
</table>

ethylene polymerizations using parallel pressure reactors and a kinetic analysis of chain transfer polymerization

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel &#945;-diimine ethylene polymerization catalyst. Initial polymerizations with the catalyst lead to optimized reaction conditions, including catalyst concentration, ethylene pressure and reaction time. Using gas-uptake data for these reactions, a procedure to calculate the initial rate of propagation (kp) is presented. Using the optimized conditions, the ability of the nickel &#945;-diimine polymerization catalyst to undergo chain transfer with diethylzinc (ZnEt2) during ethylene polymerization was investigated. A procedure to assess the ability of the catalyst to undergo chain transfer (from molecular weight and 13C NMR data), calculate the degree of chain transfer, and calculate chain transfer rates (ke) is presented.

The ethylene gas consumption versus time is presented in Figure 1 for the different ethylene pressures tested. This data is used to determine optimized reaction conditions. The ethylene gas consumption versus time is presented in Figure 2A for the catalyst alone samples, which is used to calculate the rate of propagation (kp). Figure 2B shows gel permeation chromatography (GPC) traces for chain transfer polymerizations with 0-1,000 equivalents of diet...

Watch this Scientific Journal Video about Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization at JoVE.com

Ethylene Polymerizations Using Parallel Pressure Reactors and a Kinetic Analysis of Chain Transfer Polymerization

A protocol for the high-throughput analysis of polymerization catalyst, chain transfer polymerizations, polyethylene characterization, and reaction kinetic analysis is presented.

We demonstrate a method for high-throughput catalyst screening using a parallel pressure reactor starting from the initial synthesis of a nickel ...

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12.7K visualizações.  University of Minnesota - Twin Cities.  Um protocolo para a análise de alto rendimento do catalisador de polimerização, polimerização de transferência de cadeia, a caracterização de polietileno, e a análise cinética da reacção é apresentado. 