Article

Thermotropic Liquid Crystalline Behavior of Tri-O-[4-{4′-(cyanophenylazo)phenoxy}]alkyl Celluloses
Jeong SY, Son HM, Ma YD
트리-O-[4-{4′-(시아노페닐아조)페녹시}]알킬 셀룰로오스들의 열방성 액정 거동
정승용, 손호민, 마영대

Abstract

The thermotropic liquid crystalline behavior of the homologous series of combined-type liquid crystalline polymers, tri-O-{4-(4′-cyanophenylazo)phenoxy}alkyl celluloses (CACETn, where n, the number of methylene units in the spacer, is 2~10) have been investigated. The CACETn with n of 5 and 7 exhibited enantiotropic nematic phases, while other polymers showed monotropic nematic phases. The isotropic-nematic transition temperature(TiN) increased when n is increased up to 4, but it decreased with increasing n more than 5. The entropy change at TiN also reaches a minimum at n=5, before it increases again for n=6. The sharp change at n=5 may be attributed to the difference in arrangement in the side groups. The nematic-crystalline transition temperatures, in contrast with TiNS, exhibited a distinct odd-even effect, suggesting that the average shape of the side chains in the crystalline phase is different from that in the nematic phase. The mesophase properties of CACETn were significantly different from those reported for tri-O-alkyl celluloses and poly[1-{4-(4′-cyanophenylazo)phenoxyalkyloxy}ethylene]s. The results were discussed in terms of the difference in the chemical structures of the main and side chains and the number of the mesogenic units per repeating unit.

복합형 액정 고분자 동족체들인 트리-O-[4-{4′-(시아노페닐아조)페녹시}]알킬셀룰로오스들 (CACETn, n=2∼10, 유연격자중의 메틸렌 단위들의 수)의 열방성 액정 거동을 검토하였다. n=5,7인 CACETn은 쌍방성 네마틱 상들을 형성하는 반면 다른 고분자들은 단방성 네마틱 상들을 형성하였다. 액체 상에서 네마틱 상으로의 전이온도(TiN)는 n이 4까지는 높아지나 n이 5이상에서는 n이 증가함에 따라 낮아졌다. TiN에서의 엔트로피 변화도 n=6에서 재차 증가하기 전에 n=5에서 최소치를 나타냈다. n=5에서의 급격한 변화는 곁사슬 그룹들의 배열의 차이에 의해 초래되는 것으로 생각된다. TiN들과 달리 네마틱 상에서 결정 상으로의 전이온도들은 현저한 홀수-짝수 효과를 나타냈다. 이러한 사실은 네마틱 상과 결정 상에서의 곁사슬 그룹들의 평균적인 형태가 판이함을 시사한다. CACETn의 액정 특성은 트리-O-알킬 셀룰로오스들 그리고 폴리[1-{4-(4′-시아노페닐아조)페녹시알킬옥시}에틸렌]들에 대해 보고된 결과와 현저히 달랐다. 이러한 결과들을 주사슬과 곁사슬의 화학구조 그리고 반복단위당의 mesogenic 단위들의 차이들의 견지에서 검토하였다.

Keywords: cellulose; cyanoazobenzene; spacer length; nematic phase

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This Article

2010; 34(2): 116-125

Published online Mar 25, 2010
Received on Oct 23, 2009
Accepted on Nov 30, 2009

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