旋光性聚{(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯}的合成与表征

SYNTHESIS AND CHARACTERIZATION OF OPTICALLY ACTIVE POLY{(+)-2,5-BIS[4'-((S)-(2-METHYLBUTOXYPHENYL)]BENZYL METHACRYLATE}

设计、合成了一个带有横挂三联苯侧基的手性乙烯基单体——(+)-甲基丙烯酸-2,5-二[4′-((S)-2-甲基丁氧基)苯基]苄酯,进行了普通自由基和原子转移自由基聚合反应.所得聚合物具有比单体低30°左右的比旋光度,且在侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明其主链可能形成了具有相反旋光方向的螺旋构象.在所研究范围内,聚合条件对聚合物的旋光度没有明显的影响.在分子量较小时,聚合物的比旋光度随着分子量的增加而降低,说明主链螺旋构象的贡献在增大,而当分子量达到一定值后,聚合物的比旋光度不再随分子量的增加而显著变化.

A chiral vinyl monomer, （ ＋ ）-2, 5-bis[4＇-（（ S）-（2-methylbutoxyphenyl）] benzyl methacrylate, was synthesized and polymerized via both conventional radical polymerization and atom transfer radical polymerization. The monomer showed a specific optical rotation [ α ]365^25 （ c = 0.2 g/dL） of 59.5° in THF,while the corresponding polymer displayed its [ a ]365^25 value less than that of monomer for about 30°. In the UV-Vis absorption regions of ester and p-terphenyl side-groups, the monomer exhibited very weak Cotton effects. In a sharp contrast, the polymer gave negative and positive Cotton effects centered at 302 and 270 nm, respectively. These results suggested the formation of a chiral secondary structure of polymer backbone, the optical rotation of which was opposite to that of monomer. For a vinyl polymer like poly { （ ＋ ）-2, 5-bis [4＇-（ （ S ）-（2-methylbutoxyphenyl） ] benzyl methacrylate / （PBPBMA） ,the most possible chiral structure was helical conformation of main-chain with an excess helix sense The reaction temperature and solvent were varied to study the effect of polymerization condition on the [ a ]36525 value of the polymer. It was found that the [ a 136525 value of the polymer was independent on the polymerization conditions employed. The specific optical rotations of polymers decreased with increasing molecular weight at beginning and then leveled off, consistent with the speculation of helical conformation generation. The content of mm dyads of PBPBMA was only about （PMMA）, which was co 10% as estimated with 1H-NMR by converting the polymer to poly（methyl methacrylate） mparable to that of PMMA obtained via conventional radical polymerization. This might account for the lower optical activity of PBPBMA compared to that of poly I （ ＋ ）-2, 5-bis [ 4＇-（ （ S ）-2- methylbutyloxy） phenyl] styrene}, an optically active helical vinyl polymer with similar structure.