Divinylbenzene cyclopolymerization

It has been suggested that certain 1,5-dienes including o-divinylbenzene (23),156 vinyl acrylate (24, X 11) and vinyl methacrylate (24, X CH )120 may also undergo cyclopolymerization with a monomer addition occurring prior to cyclization and formation of a large ring. However, the structures of these cyclopolymers have not been rigorously established. 

It is noteworthy that the formation of cyclic structures is not confined to diallyl esters. For example, Haward and Simpson found evidence for cyclopolymerizations at low conversion of solutions of divinylbenzene in styrene [48]. Diallyl ammonium halides were among early examples of cyclopolymerizations [49]. Two reviews of interest are Marvel [50] and Butler [51]. 

Further examples of cyclopolymerization have been cited. Divinyl ether gives polymers containing bicyclic units. The polymerizations of 1,4-divinylbenzene and 1,3,5-trivinylbcnzene have been investigated. Ring-opening radical polymerizations for derivatives of vinyl cyclopropane have been described... 

More examples have been quoted of special growth reactions for molecules having two carbon-carbon double bonds. Cyclopolymerization occurs for diallylaminomethyl phenols, allyl esters of unsaturated acids, 2-(2-vinyl-phenoxy)ethyl methacrylate and acrylate, 2-divinylbenzene and some silicon-containing monomers. - Polymerizations of p-xylylene and its derivatives have been considered further. - The radical polymmzation of some disubstituted vinylcyclopropanes has been represented as shown in equation (2), where X and Y=CN or COjEt. The involvement of the ring must be connected with stabilization by the substituents of the product radical. 

Anionic polymerization of o-divinylbenzene was examined by Aso et al. [294]. The authors used n-BuLi, phenyllithium, and naphthalene/alkali metal in THF, ether, dioxane, and toluene at temperatures between —78 and 20 °C. Generally, it was found that as with radical and cationic initiators, a competition between cyclopolymerization and conventional 1,2-polymerization occurs, with the tendency for cyclization to be lower than with the other mechanisms. The polymerization initiated with the lithium organic compounds resulted in polymers with up to 92% double bonds per monomer unit (THF, 20 °C). Polymerization with lithium, potassium, and sodium naphthalene also showed a rather weak tendency for cyclization. In THF at 0°C and 20 °C the cyclization tendency increased with decreasing ionic radii of the counter cation, while in dioxane the reverse effect was observed, and in ether still another dependence was found (K > Li > Na). Nitadori and Tsuruta [299] used lithium diisopropyl amide in THF at 20 °C to polymerize m- and p-divinylbenzene. The authors obtained soluble products with molecular weight up to 100 000 g/mol (GPC) and showed the polymers to contain pendant double bonds by IR and NMR spectra. It seemed to be important that a rather large excess of free amine (the initiator was formed by reaction of -BuLi with excess diisopropylamine) was present in the polymerization mixture. In later studies [300,301] a closer view was taken on polymerization kinetics and the steric course of the polymerization reaction. 

Polymerization of divinyl compounds (e.g., divinylbenzene) under usual acidic conditions results in cross-hnked insoluble polymers. By selecting reaction conditions, however, it is possible to obtain non-cross-linked, soluble polymers in which cyclic repeating units are incorporated into the main chain. One of these processes is the so-called cyclopolymerization (Eq. (9)) that involves an intramolecular cycliza-tion of the propagating species. Abundant examples of this, both radical and ionic, are known... 

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