基于2,5-二(4′-甲酰基苯基)苯乙烯的螺旋链光学活性聚合物的合成与表征

通过2,5-二溴苯乙烯与对甲酰基苯硼酸的Suzuki偶联反应得到2,5-二(4′-甲酰基苯基)苯乙烯.在催化剂量的冰乙酸存在下,与光学纯的(S)-(-)-α-甲基苄胺或(R)-(+)-α-甲基苄胺发生缩和反应,得到了一对手性非外消旋单体,(+)-2,5-二{4-′(N-(S)-α-甲基苄亚胺基)次甲基]苯基}苯乙烯和(-)-2,5-二{4′-(N-(R)-α-甲基苄亚胺基)次甲基]苯基}苯乙烯.以偶氮二异丁腈(AIBN)或过氧化苯甲酰(BPO)为引发剂,经自由基溶液聚合得到光学活性聚合物.比旋光度、紫外-可见吸收光谱以及圆二色光谱研究表明,聚合物主链可能形成了某一方向占优的稳定螺旋构象,且该螺旋构象的旋光方向与单体的旋光方向相反.聚合条件对聚合物的光学活性有很大影响,在极性较大的芳香族溶剂和较高温度下得到的聚合物具有和单体相差更大的比旋光度.侧基的手性基团脱除后,聚合物仍具有一定的旋光性,说明聚合过程中形成的螺旋手性具有一定的记忆效应.

SYNTHESIS AND CHARACTERIZATION OF OPTICALLY ACTIVE HELICAL POLYMERS BASED ON 2,5-DI(4′-FORMYLPHENYL)STYRENE

2,5-Di(4′-formylphenyl)styrene was synthesized via Suzuki cross-coupling reaction of 2,5-dibromostyrene and p-formylphenylboronic acid.In the presence of catalytic amount of glacial acetic acid,a pair of chiral nonracemic vinyl monomers,(+)-2,5-di {4′-(N-(S)-α-methylbenzylimine)methylene]phenyl}styrene(M 1)and(-)-2,5-di {4′-(N-(R)-α-methylbenzylimine)methylene]phenyl}styrene(M 2),was synthesized through the condensation reaction between 2,5-di(4′-formylphenyl)styrene and optically pure α-methylbenzylamine.Optically active polymers were prepared via free radical polymerization of M 1 and M 2 initiated by AIBN or BPO depending on polymerization temperature.The results from specific optical rotation,UV-Vis absorption spectra and circular dichroism spectra indicated that the polymer obtained might adopt a helical conformation with a predominance of one helical screw sense.The polymerization condition had pronounced effects on the chiroptical properties of the polymers.Polymer with larger helical chirality was obtained when the polymerization was carried out in more polar aromatic media at higher temperature.Due to the steric hindrance of the bulky p-terphenyl groups,the main chain helical chirality formed during polymerization was thermally stable and displayed memory effect.