甲壳素类液晶高分子的研究V.取代基个数及长度对羟乙基壳聚糖液晶性的综合影响

采用碱壳聚糖的方法合成了一系列具有不同摩尔醚化度 (DME)的新的液晶性壳聚糖衍生物羟乙基壳聚糖 (HECS) .用酸氧化蚀刻的方法 ,在扫描电子显微镜 (SEM )下证实了其胆甾型的液晶织构 .以甲酸为溶剂 ,研究了摩尔醚化度对羟乙基壳聚糖溶致液晶性的影响 .结果表明 ,在该体系中 ,摩尔醚化度能综合取代基个数及长度两个结构因素的影响 ,当DME较低时 (<～ 2 0 ) ,这种影响关系类似于取代基个数 (即取代度 )的影响 ,当DME较高时 (>～ 2 0 ) ,则类似于取代基长度的影响 .前者对液晶临界浓度的影响很小 ,而后者却有显著影响 .此外还观察到当DME >～ 2 0时出现水溶性 ,HECS的水溶液也呈现典型的胆甾指纹状织构

STUDIES ON CHITIN|BASED LIQUID CRYSTALLINE POLYMERS V. INTEGRATED INFLUENCE OF NUMBER AND LENGTH OF SUBSTITUENT ON HYDROXYETHYL CHITOSAN

A novel liquid crystalline polymer-hydroxyethyl chitosan(HECS) was synthesized in alkali system.The degree of molar etherification(DME) of HECS was controlled by both the amounts of ethylene oxide and the reaction time.DME of HECS specimens was from 0^2 to 5^4 measured by element analysis and NMR.All specimens formed typical cholesteric texture——fingerprint texture while dissolved in formic acid.HECS with DME>1^9 was water soluble,and the HECS aqueous solution also formed cholesteric phase with typical texture.The mesophase texture was detected both by polarized optical microscopy and scanning electron microscopy.Samples for SEM studies were treated by permanganic etching in order to increase the contrast.The studies were focused on the effect of DME on the critical concentration(c+·) of mesophase formation for HECS/formic acid solutions.The results indicated that c+· sharply increased with DME at first,and became independent as DME varied from 0^2 to 1.9. After that(DME>1.9),it regain obvious rise as DME continuously heightened.These results were explained by the variation of both persistence length q and molecular diameter d in Flory's semi|experience equation c+·≈8q/x(x=2q/d).The variation of DME of HECS related with two structural factors,i.e.the number and length of the substituent,the former affected c+· slightly,but the latter affected c+· evidently.