Diolefins, free radical polymerization

It is evident that the tendency for free radical polymerization is a function of the monomer. Natta (287) stated that these radicals can initiate polymerization of styrene and diolefins to high molecular weight products but not that of aliphatic alpha olefins. North (339) showed that the decomposition of phenyl tri-isopropoxy titanium initiates radical polymerization of styrene but not of ethylene. 

Catalysts of the Ziegler type have been used widely in the anionic polymerization of 1-olefins, diolefins, and a few polar monomers which can proceed by an anionic mechanism. Polar monomers normally deactivate the system and cannot be copolymerized with olefins. However, it has been found that the living chains from an anionic polymerization can be converted to free radicals in the presence of peroxides to form block polymers with vinyl and acrylic monomers. Vinylpyridines, acrylic esters, acrylonitrile, and styrene are converted to block polymers in good yield. Binary and ternary mixtures of 4-vinylpyridine, acrylonitrile, and styrene, are particularly effective. Peroxides are effective at temperatures well below those normally required for free radical polymerizations. A tentative mechanism for the reaction is given. 

Historically, the development of the intra-intermolecular polymerization can be traced back to early studies on free-radical polymerizations and copolymerizations of diolefinic monomers. According to Staudinger 150), the polymerization of nonconjugated dienes should yield cross-linked polymers. However, studies of the free radical-initiated copolymerizations of methyl methacrylate with ethylene dimethacrylate, and of vinyl acetate with divinyl adipate 165) have shown the existence of a delay in reaching the gel point. In other words, for some unexplained reason the gel point was reached at... 

Addition polymerization is employed primarily with substituted or unsuhstituted olefins and conjugated diolefins. Addition polymerization initiators are free radicals, anions, cations, and coordination compounds. In addition polymerization, a chain grows simply hy adding monomer molecules to a propagating chain. The first step is to add a free radical, a cationic or an anionic initiator (I ) to the monomer. For example, in ethylene polymerization (with a special catalyst), the chain grows hy attaching the ethylene units one after another until the polymer terminates. This type of addition produces a linear polymer ... 

Vinyl-type addition polymerization. Many olefins and diolefins polymerize under the influence of heat and light or in the presence of catalysts, such as free radicals, carbomum ions or carbamons. Free radicals are particularly efficient in starting polymerization of such important monomers as styrene, vinylchloride, vinylacetate, methylacrylate or acrylonitrile. The first step of this process—the so-called initiation step—consists in the thermal or photochemical dissociation of the catalyst, and results in the formation of two free radicals-. 

Medvedev has reported work on the kinetics of polymerization of diolefins and other compounds, as influenced by the number of free radicals in the reaction (230). In the polymerization of styrene, two chain reactions are thought to take place the reaction of free radicals with oxygen leads to oxidation, and the reaction with styrene to polymerization (231). 

Geomelrical isomerism of polymers made from conjugated diolefins can be regulated in some anionic polymerizations. The tacticity of vinyl polymers is, however, not always controlled in anionic reactions. The products of anionic vinyl polymerizations are usually atactic, as in free-radical syntheses. 

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