ABSTRACT:The radical telomerization of methyl methacrylate (MMA) was carried out at 50-90oC using bromotrichloromethane (BTCM) as a chain transfer agent, and the n[MMA]: [BTCM] adducts, that is, the n-mers, where, n= 1-3, were separated by silica-gel column chromatography. The tacticities of two dimers and three trimers were estimated by 1 H NMR spectroscopy. Syndiotactic diastereoisomers were formed preferentially, and no isotactic trimer was found. The most stable conformations of the syndiotactic-and isotactic-dimers were presumed from the results of induced reactions.

ABSTRACT: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 estO!r 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· 1 H 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.

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The radical telomerization of isopropyl (IPMA) and t-butyl (TBMA) methacrylates was carried out using bromotrichloromethane as a telogen at 50, 70, and 90°C, and compared with that of ethyl methacrylate (EMA). The telomerization behavior of these monomers and reactivity of the resulting telomers were greatly dependent on the kinds of alkyl substituents in the ester groups. The average degree of telomerization decreased, whereas the yield of lactones increased, with increasing degree of branching in the alkyl chain. The telomerization of IPMA gave the syndiotactic (st) dimeric telomer in preference to the isotactic one in a ratio around 85: 15, which was almost identical with the value in the telomerization of EMA. In the telomerization of TBMA, however, all the dimeric telomer which was produced at reaction temperature below 70°C, was the st one. Furthermore, the formation of carboxylic acid compounds was observed only in the telomerization of TBMA. The lactonization of dimeric-and trimeric-telomers was induced by the catalytic action of silica gel and heat. The IPMA telomers resembled EMA ones in the reactivities of lactonization. On the other hand, the TBMA telomers were greatly subject to lactonization in comparison with others. Lactones resulting from the TBMA telomers were further transformed into corresponding carboxylic acids. The carboxylation of TBMA lactones was promoted by the catalytic action of t-butyl bromide.