Phenyl acetylene thermal polymerization

Attempts to elucidate the polymerization or copolymerization kinetics of ethynyl and maleimide-functionalized monomers have been undertaken via vibrational spectroscopy (137). The thermal polymerization of A-(3-ethynyl-phenyl) maleimide (the structure is given in Fig. 48) was studied via IR and Raman spectroscopy. This model compound is interesting because it carries maleimide and ethynyl groups attached to the same aromatic ring. Kinetic studies indicate that both the acetylene and maleimide group react at the same rate, which strongly suggests the formation of a copolymer rather than a mixture of homopolymers. 

The most interesting application from an industrial point of view is the cobalt-catalyzed one-step synthesis of 2-vinylpyridine from acetylene and acrylonitrile (eq. (10)). In this way the fine chemical can be manufactured using equal amounts by weight of the comparatively inexpensive components, acetylene and acrylonitrile. The 2-vinylpyridine synthesis must be carried out in pure acrylonitrile below 130-140 °C, otherwise acrylonitrile and the product 2-vinylpyridine undergo thermal polymerization [34]. Therefore only very active catalysts can be applied in the reaction of eq. (10). The best results were obtained using i/ -l-phenyl-borininatocobalt cod as the catalyst (productivity 2.78 kg 2-vinylpyridine per g cobalt [5 ej. 

Monomers Not Polymerizable by Plasma Initiation. When styrene and a-methy1styrene were subjected to plasma treatment, the monomers became yellowish and only trace amounts of insoluble films were formed. The discoloration was intensified and extensive formation of dark films were observed if carbon tetrachloride was added as the solvent. No post-polymerization was detectable for these monomers. Generally styrene and a-methylstyrene readily undergo thermal polymerization. However, no thermal polymerization was possible for these monomers after having been subjected to plasma treatment for one minute or less. It has been demonstrated from the emission spectra of glow discharge plasma of benzene (6) and its derivatives (7 ) that most of the reaction intermediates are phenyl or benzyl radicals which subsequently form a variety of compounds such as acetylene, methylacetylene, allene, fulvene, biphenyl, poly(p-phenylenes) and so forth. It is possible that styrene and a-methylstyrene also behave similarly, so that species from the monomer plasma are poor initiators for polymerization. 

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