ISSN:
0449-2951
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The polymerization of 1,3-butadiene with several catalytic CoCl2-AlCl3 compositions is described. Blue solid products of the reaction of CoCl2 with AlCl3 in which Co is coordinated in an octahedral configuration, are ineffective as stereospecific catalysts, unless they are treated with an aromatic hydrocarbon to yield a solution of a mixture of a green catalytic Co(AlCl4)2 complex, in which the Co coordination has a square planar configuration, and AlCl3 which is comparatively inert under polymerization conditions. This mixture forms regardless of the resulting (and frequent varying) molar ratio of Al to Co in solution, and regardless of whether the solid products contain AlCl3 that is not complexed with Co. Similar solutions result from the reaction of CoCl2 with AlCl3 in an aromatic hydrocarbon. In the absence of a modifier a benzene solution of a Co(AlCl4)2 complex catalyzes stereoregular and nonstereoregular polymerizations to about an equal extent. However, the addition of thiophene favors cis polymerization at the expense of the nonstereoregular polymerization, and a quantitative yield of polybutadiene with 94-99% of its unsaturation in the cis configuration and a sulfur content corresponding to one thiophene endgroup per polymer molecule was thereby obtained. Cis content and conversion reached a maximum at thiophene levels of 300 mole-% based on AlCl3. At lower thiophene levels, conversion, unlike cis content, passed through a minimum before reaching a maximum. Polymers with a similarly high cis content were also obtained in the absence of thiophene by preparing oily catalyst compositions in toluene or xylene in the presence of traces of aluminum, magnesium or zinc powders which are believed to serve mainly as proton scavengers. The stereospecificity of the catalytic solutions was essentially independent of the ratio of Al to Co in solution. A possible mechanism consistent with polymerization data is discussed. It is suggested that stereoregular polymerization involves the attachment of thiophene and butadiene to one aluminum atom of the Co(AlCl4)2 complex in which Co is coordinated in a square planar configuration, by displacement of chloride ions from this aluminum atom to vacant coordination positions about the cobalt atom, resulting in an octahedral configuration about cobalt, followed by a cycloalkylation reaction between the coordinated thiophene and butadiene and subsequent insertion of butadiene into the polymer chain by a sequence of similar cycloalkylation reactions.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1964.100020721
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