Copolymers ring-opening reactions involving

Several important assumptions are involved in the derivation of the Mayo-Lewis equation and care must be taken when it is applied to ionic copolymerization systems. In ring-opening polymerizations, depolymerization and equilibration of the heterochain copolymers may become important in some cases. In such cases, the copolymer composition is no longer determined by die four propagation reactions. 

Free radical polymerization of cyclic ketene acetals has been used for the synthesis of polyfy-butyrolactone), which cannot be prepared by the usual lactone route due to the stability of the five-membered ring. The polymerization of 2-methylene-l,3-dioxalane at high temperatures (above 120 °C) gave a high molecular mass polyester [59,79]. Only 50% of the rings opened when the polymerization was carried out at 60 °C, and this led to the formation of a random copolymer. The presence of methyl substituents at the 4- or 5-position facilitated the reaction. The free radical initiators generally used in such polymerizations are ferf-butyl hydroperoxide, ferf-butyl peroxide, or cumene hydroperoxide. The various steps involved are described in Scheme 5 [59]. 

This copolymer is identical to the one obtained from reacting 2-oxazolone with jff-propiolactone. The acrylic acid is converted into the same repeat unit as the one that forms from ring opening of j -propiolactone shown in the previous example. The suggested reaction mechanism involves a nucleophilic attack by oxazolone on acrylic acid and is followed by proton migration ... 

A similar mechanism has been postulated for reactions involving cycloalkenes. It has been shown that a copolymer of cyclooctene and cyclopentene (labelled on its double bond with is predominantly labelled in the C5 fragment, this result being obtained by reductive ozonolysis of the polymer [9j. The radioactivity found in the C5 diol proves that ring opening polymerization also proceeds via scission on the double bonds rather than cleavage of carbon—carbon single bonds. 

This section deals with investigations specifically aimed at producing homopolymers and copolymers of furan carbonyl compounds by the selective opening of the carbonyl bond. The many reports on polymerization of 2-furaldehyde which in fact deal with complicated acid-catalysed resinification reactions which involve both the formyl group and the furan ring are reviewed in Chapter VI. 

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