以聚乳酸为侧链的光学活性聚苯乙炔的合成与表征

SYNTHESIS AND CHARACTERIZATION OF OPTICALLY ACTIVE POLY(PHENYLACETYLENE) WITH POLYLACTIDE SIDE CHAINS

通过4-溴苯甲醇和三甲基硅基乙炔的Sonagashira偶联反应与三甲基硅基的脱除反应,合成4-乙炔基苯甲醇.以4-乙炔基苯甲醇为引发剂,以有机氮杂环化合物DBU为催化剂,常温常压下进行丙交酯的活性开环聚合反应,采用1H-NMR和GPC对产物结构、分子量与分子量分布进行表征分析,结果表明,合成以了苯乙炔为端基的聚乳酸大分子单体PA-PLLA-3k、PA-PLLA-4k、PA-PDLA-3k和PA-PDLA-4k,实现了分子量的有效控制.以[Rh(nbd)Cl]2/Et3N为催化剂,实现了大分子单体的均聚,得到以聚乳酸为侧链的聚苯乙炔poly-(PA-PLLA)-3k,poly(PA-PLLA)-4k,poly(PA-PDLA)-3k和poly(PA-PDLA)-4k.采用GPC、GPC-MALLS和1H-NMR对聚苯乙炔进行表征分析,结果表明poly(PA-PLLA)和poly(PA-PDLA)均具有较高的分子量,分子链呈线形柔性链形态.CD和UV-Vis光谱分析表明poly(PA-PLLA)和poly(PA-PDLA)主链均形成了螺旋构象,而且Cotton效应的方向受大分子单体手性的影响,大分子单体的手性相同,聚苯乙炔主链Cotton效应的方向相同,大分子单体的手性相反,聚苯乙炔主链Cotton效应的方向相反;在不同溶剂中聚苯乙炔主链螺旋构象的规整程度不同;聚苯乙炔螺旋构象的稳定性随着温度的提高而降低.

Sonagashira coupling reaction between 4-bromobenzyl alcohol and trimethylsilylacetylene was carried out and then the trimethylsilyl group was removed to give 4-ethynylbenzyl alcohol. Living ring-opening polymerization of lactide was performed under normal pressure and temperature by using DBU as a catalyst and 4-ethynylbenzyl alcohol as an initiator. ^1H-NMR spectra and GPC were employed to characterize the chemical structure of the products and analyze the molecular weight and polydispersity. The results indicated that polylactide macromonmers bearing 4-ethynylbenzyloxy end group （ PA-PLLA-3k, PA-PLLA-4k, PA-PDLA-3k, and PA-PDLA4k） were successfully synthesized, and the molecular weight of the macromonmers was controlled effectively. Homopolymerization of the macromonomers was carried out by using [ Rh （nbd） C112/ Et3N as the catalyst to give poly （phenylacetylene）s with polylactide side chains （poly （PA-PLLA）-3k, poly- （PA-PLLA）-4k, poly（PA-PDLA）-3k and poly（PA-PDLA）-4k）. The poly（phenylacetylene） s were characterized by GPC, GPC-MALLS and X H-NMR. The results indicated that poly （PA-PLLA） and poly （PA- PDLA） possess linear flexible chain with high molecular weight. CD and UV-Vis spectra of the poly- （phenylacetylene） s showed that poly（PA-PLLA） and poly（PA-PDLA） main chains assuredly possess predominantly one-handed helical conformations, and the direction of Cotton effects was affected by the chirality of macromonomers. The direction of Cotton effects of the poly（phenylacetylene） s was the same when the chirality of macromonomers was the same, Cotton effects of the poly（phenylacetylene） s were reverse when the chirality of macromonomers was reverse. The intensity of Cotton effects was various in different solvents, this meant that the regularity of helical conformation of the poly （phenylacetylene） main chain was variable in different solvents. Moreover,the stability of helical conformation of poly （phenylacetylene） decreased with the increasing temperature.