熱刺激去極化電流法研究液晶聚合物分子運動現象

Abstract

本研究係以熱刺激去極化電流及緩和圖譜分析(TSC/RMA)研究側鏈型及主鏈液晶聚合物之分子運動行為。在第一系列的側鏈液晶共聚矽氧烷中,本研究以 TSC/RMA探討此類聚合物雙玻璃轉移溫度行為，並研究側取代基、高分子主鏈以及柔軟間距對於主鏈及側鏈分子運動之影響，結果顯示柔軟間距愈長，高分子主鏈愈柔軟及無側取代基，液晶之分子運動較容易。在第二系列的鐵電性側鏈液晶聚環氧丙烷中，本研究以 TSC/RMA探討其玻璃轉移溫度及側鏈液晶基分子運動以及聚合物之鐵電性，結果證實 TSC 無法測得此聚合物之鐵電性。對於第三與第四系列側鏈液晶共聚甲基丙烯酸酯及共聚丙烯酸酯，本研究 TSC/RMA 可以很清楚的觀察到玻璃轉移溫度和側鏈液晶基縱向分子運動波峰，研究結果顯示所合成共聚物只有一個玻璃轉移點，而液晶共聚甲基丙烯酸酯之玻璃轉移溫度比純聚甲基丙烯酸酯低，至於液晶共聚甲基丙烯酸酯之玻璃轉移溫度溫度卻比純聚丙烯酸酯高，顯現側鏈團基對於玻璃轉移分子運動有相當程度的影響。 一般主鏈液晶聚合物以微差掃描卡計(DSC)不容易觀察到其玻璃轉移點，本研究第二部份以TSC/RMA探討主鏈液晶聚合物之分子運動行為，在第五系列含4-羥基-3,5-二溴苯甲酸單體之液晶共聚酯中，TSC可以很清楚的測量到其玻璃轉移溫度，研究結果顯示導入4-羥基3,5-二溴苯甲酸單體於棒狀液晶聚酯中，可以有效的降低所合成聚合物之熔點及玻璃轉移溫度。 至於第六系列液晶聚酯，TSC可以明顯的偵測到DSC無法測得的玻璃轉移溫度，對於液晶聚酯和聚醚硫風共聚合物，DSC所偵測到的玻璃轉移溫度範圍非常寬廣，TSC/RMA則可以很準確的觀測到其玻璃轉移溫度，顯示TSC是測量主鏈液晶聚合物的良好工具。

Thermally stimulated current and relaxation map analysis (TSC/RMA) are used to study the molecular dynamics of main-chain and side-chain liquid crystalline(LC) polymers. In the frist series of side-chain liquid crystalline copolysil-oxanes, the dual glass transitions as well as effect of spacer length, polymer backbone and lateral substitution on the molecular dynamics, are investigated byTSC/RMA. The results demonstrate that a longer spacers, a more flexible polymerbackbone and a smaller lateral subsitituent will lead easier moving of the sidegroup molecules. In the second series of ferroelectric side-chain LC polyoxetanes , the glass transition, side-chain motions as well as ferroelectric propertiesof the obtained polymers are studied by TSC/RMA. The results demonstrate that ferroelectric mode, i.e. Goldstone mode, can not be observed in the TSC measure-ment. TSC/RMA are used to study the third and forth series of side-chain LC poly-methacrylates and polyacrylates. All of the LC polymethacrylates and polyacrylatesreveal a glass transition and a depolarization peak which is attributed to the motions of the longitudinal components of the dipole moment of the longitudinalcomponents of the dipole moment of the mesogenic side groups on the TSC curves. All obtained LC polymethacrylates show a glass transition temperature lower than that of poly(methyl methacrylate) and all obtained LC polyacrylates presenta glass transition higher than that poly(methyl acrylate). The results indicatethat the side group has prominent effect on the glass transition temperature. The glass transition is generally difficult to be observed in the DSC measure-ments. The glass transition as well as molecular dynamics of some main-chain LCpolymers are investigated by TSC/RMA also. In the fifth series of LC polyesterswhich containing the 4-hydroxy-3,5-dibromobenzoic acid monomer, their glass tran-sition are observed on the TSC curves. The results demonstrate that introducingthe 4-hydroxy-3,5-dibromobenzate unit into the rigid-rod polyesters decreasesthe melting points and glass transition temperatures of the obtained copolyesters. The TSC is also used to study the glass transition of a series of LC polyestersand their block copolymers with polyether sulfone. The LC polymers which displayno glass transition on the DSC scans, however, reveal very clear glass trasition on TSC curves. The block copolymers of LC polyesters and polyether sulfone whichdisplay very broad glass transition DSC curves, show very sharp glass transitionpeaks on the TSC curves. The results indicate that TSC is a very useful techniqueto study the glass transition of the main-chain LC polymers