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Study on Radical Telomerization of Esters of Methacrylic Acid by Using Bromotrichloromethane and Characteristics of the Resulting Telomers II. Primary Alkyl Methacrylates

Radical telomerization of methyl, ethyl, propyl, and butyl methacrylates was carried out by using bromotrichloromethane (BTCM).as a chain transfer agent at 50, 70, and 90°C. This series of primary alkyl methacrylates showed a similar temperature dependence of the telomerization behavior, but no significant effect of the alkyl chain length of the ester group was observed in the telomerization. The n[Monomer]:[BTCM] adducts, that is, the n-mers (n=1–3), were separated by silica gel column chromatography. The increase of the molecular flexibility by increasing the alkyl chain length of the ester group caused a decrease of the melting point in the homologous telomers. The stereochemistry and the reactivity of the homologous telomers were studied by comparing the 1H NMR spectra and the reactions of dimers. The elimination reaction of dimers with triethylamine gave both two isomeric unsaturated compounds and two isomeric lactones. Heating of dimers in the absence of solvent resulted in the lactonization selectively, and a similar reaction was also observed by the catalytic action of silica gel. The processes of lactonization of the telomers were mechanistically elucidated.