甲壳素类液晶高分子的研究Ⅶ.N,O-苄基壳聚糖的胆甾螺旋行为

N ,O-苄基壳聚糖在浓溶液中形成胆甾液晶相 .用圆偏光二向色性谱 (CD)研究了这一聚合物的螺旋行为 ,主要包括螺距和螺旋方向 .浓度越高 ,螺距P越大 ,意味着胆甾相的扭转力随浓度增加而减弱 .CD谱图上观测到两类吸收 ,即在 5 70nm附近较宽但较强的吸收和 330nm附近较尖但较弱的吸收 .前者归属于胆甾相层片的超分子螺旋构象 ,而后者可以归属于分子链的螺旋构象 .改变浓度或溶剂性质时这两个层次的构象都会发生符号的变化 .提高浓度 (固定二氧六环为溶剂 )时两种螺旋结构先后发生反转 .以氯仿为溶剂 (固定浓度为 6 5 % )时两种螺旋结构均为左旋 (正Cotton效应 ) ,但二氧六环和四氢呋喃为溶剂时均变为右旋 (负Cotton效应 ) .溶剂的影响可能与溶剂和高分子间形成氢键的能力有关

STUDIES ON CHITIN-BASED LIQUID CRYSTALLINE POLYMERS Ⅶ. HELICOIDAL BEHAVIOR OF CHOLESTERIC LIQUID CRYSTALS FOR N,O-BENZYL CHITOSAN

N,O Benzyl chitosan formed cholesteric liquid crystalline phase in concentrated solutions.The helicoidal behavior (including mainly helix pitch and twist sense) of this polymer was studied by means of circular dichroism (CD).The higher the concentration was,the larger the pitch was,implying the twisting power decreased with the increase of concentration.Two kinds of absorption can be observed in CD spectra.A broad and strong band appeared at 570 nm,but another sharp and weak band appeared at 330 nm.The former arose from the supermolecular helicoidal structure of cholesteric layers; the latter may arise from the helical conformation of chains.Both levels of helicoidal structures changed their signs,when the concentration or solvent varied.When the solution concentration increased (using dioxane as solvent),the two levels of helicoidal structures inversed from left handed to right handed one by one.When chloroform was used as solvent and the concentration was 65wt%,the handedness of the two helicoidal structures was left handed (positive Cotton effect),but when dioxane or THF was used with the same concentration,a reversed handedness was observed.The influence of solvent may be related to the formation of hydrogen bonds between the solvent molecules and the polymer chains.