摘要
设计、合成了一系列含有手性烷氧基末端的乙烯基二联苯单体,进行了普通自由基、原子转移自由基以及负离子聚合反应.所有单体中,只有手性烷氧基苯基位于乙烯基邻位的聚合物的比旋光度与其单体相比有比较大的区别,且在对应于其侧基的紫外吸收处呈现明显不同于单体的Cotton效应,说明可能形成了某一方向占优的螺旋构象.在所研究范围内,聚合条件和聚合物分子量对聚合物的旋光度没有明显的影响.比较负离子聚合和自由基聚合所获得聚合物的比旋光度发现,负离子聚合有利于增加聚合物螺旋链构象的完整性.切除能形成螺旋链的聚合物侧基上的手性烷氧基,所得到的聚合物虽然不含手性原子但依然表现出光学活性,说明其具有一定的手性记忆效应.
A series of vinyl biphenyl monomers containing chiral alkoxy terminals were synthesized and polymerized via conventional radical polymerization,atom transfer radical polymerization and anionic polymerizations.Optical polarimetry and circular dichroism spectroscopy were employed to characterize the chiroptical properties of model compounds,monomers and polymers.It was found that only the monomers with chiral alkoxy phenyl located at the ortho position of vinyl group were able to yield the polymers displaying a specific optical rotation ^（25）_（365） different obviously from their precursors and model compounds.These polymers also displayed cotton effects in the UV-Vis absorption region of biphenyl side-group,in a sharp contrast to the monomers,suggesting the formation of a chiral secondary structure of polymer backbone.For vinyl polymers,the most possible chiral structure was helical conformation of main-chain with an excess helix sense.Furthermore,the helical polymer containing chiral alkoxy group at meta-position,i.e.P3M2St,showed an [α]^25 365 value larger than that of monomer,while the helical polymer containing chiral alkoxy group at para-position,i.e.P4M2St,showed less intensive optical rotation than its monomer,indicating opposite helical sense of main-chain conformation.The reaction temperature and solvent were varied to study the effect of polymerization condition on the [α]^25 365 value of polymers.It was found that the [α]^25 365 value of polymers was independent on not only the polymerization condition employed but also the molecular weight of the polymer studied.The helical polymers obtained via anionic polymerization exhibited a larger difference in ^25 365 from monomer than those resultant from radical polymerization,implying that the anionic polymerization had advantage of obtaining stereoregular structure.After removal of chiral alkoxy groups,the optically active helical polymers obtained showed optical rotations even larger than their precursor polymers although no stereogenic center was presented in the molecule,suggesting somewhat ＂memory effect＂.
出处
《高分子学报》
SCIE
CAS
CSCD
北大核心
2010年第2期222-230,共9页
Acta Polymerica Sinica
基金
国家自然科学基金(基金号20674001)
国家杰出青年科学基金(基金号20325415)
中国博士后科学基金(基金号20080440249)资助项目
关键词
旋光性螺旋链聚合物
记忆效应
自由基聚合
原子转移自由基聚合
负离子聚合
Optically active helical polymer Memory effect Radical polymerization Atom transfer radical polymerization Anionic polymerization
