Methylene compounds, double-bonded polymerization

Studies on the polymerization of various 4-methylene-l,3-dioxolans [94] by BF3Et20 or A1C13 showed that 4-methylene-l,3-dioxolan itself polymerises mainly through the double bond the 2-methyl and 2,2-dimethyl compounds gave polymers with a variable carbonyl content. This arises from a co-polymerization in which units of type (VII) and (VIII) are incorporated in the chain in different proportions, according to the reaction conditions ... 

The key substrates for conjugate addition are the a, 3-unsaturated carbonyl compounds. When the double bond is inside a chain or ring these compounds are available via a wide variety of routes including the aldol reaction and are generally stable intermediates that can be stored for use at wiU. When the double bond is exo to the ring or chain (exo-methylene compounds), the unhindered nature of the double bond makes them especially susceptible to attack by nucleophiles (and radicals), This reactivity is needed for conjugate additions but the compounds are unstable and polymerize or decompose rather easily,... 

Reviews on radical ring-opening polymerization include those by Sanda and Endo, " Klemm and Schultz, Cho, " Moszner e( Endo and Yokozawa Stansbury and Bailey. A review by Colombani on addition-fragmentation processes is also relevant. Monomers used in ring-opening are typically vinyl (e.g. vinylcyclopropane - Scheme 4.20 Section 4.4.2.1) or methylene substituted cyclic compounds (e.g. kctenc acetals - Section 4.4.2.2) where addition to the double bond is followed by p-scis.sion. 

Won et al. [19], have reported synthesis of polyesters with valine, leucine, isoleucine, methionine, and phenylalanine (Table 12.1). This three-step process involves synthesis of a diester and a dinitro compound that are copolymerized [19], An amino acid is first coupled with a diol (with 3, 4, or 6 methylene groups) in the presence of tosyl to yield a diester with acid salts of diamine at the terminal ends. The second monomer, di-p-nitrophenyl ester of carboxylic acids, is synthesized by a condensation reaction of adipoyl or se-bacoyl chloride with p-nitro phenol. The final polymerization step involves an arduous condensation reaction in the presence of a strong proton abstractor between acid salt of bis(amino acid-alkyne diester) and di-p-nitrophenyl ester of dicarboxylic acids. Following along the same lines, Chu and Guo [22] have copolymerized a mixture of nitro phenyl ester of succinate, adipate, or sebacate and nitrophenyl fumarate with toluenesulfonic acid salt of phenylalanine butane-1,4-diester. The addition of fumarate derivative to the monomer mixture provides an unsaturated double bond in the polymer backbone that can be functionalized for specific biomedical... 

The initiation step is similar to that described for beta-pinene as illustrated in Figure 6. Propagation through the terminal methylene group would be predicted. However, the determination of olefin content by NMR, ozonolysis and perbenzoic acid oxidation indicates that approximately one-half of the mer units have unsaturation. The endocyclic or ring double bond is thus involved in the polymerization and is consumed in some manner. To substantiate this theory, the structurally similar model compound 8,9-p-menthene was polymerized under identical conditions. Only dimer was obtained. The double bond in the ring thus permits successful polymerization of dipentene. 

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