Article
  • Thermotropic Liquid Crystalline Behavior of Poly[1-{4-(4′-cyanophenylazo)phenoxyalkyloxy}ethylene]s
  • Jeong SY, Lee JY, Ma YD
  • 폴리[1-{4-(4′-시아노페닐아조)펜옥시알킬옥시}에틸렌]들의 열방성 액정 거동
  • 정승용, 이재윤, 마영대
Abstract
A homologous series of side chain liquid crystalline polymers, poly[1-{4-(4′-cyanophenylazo) phenoxyalkyloxy}ethylene]s(CAPETn, where n, the number of methylene units in the spacer, is 2∼10) were synthesized from poly(vinyl alcohol) and 1-{4-(4′-cyanophenylazo)phenoxy}alkylbromides (CAPBn, n=2∼10), and their thermotropic liquid crystalline phase behaviors were investigated. The CAPBn with n of 2∼5 did not show any liquid crystalline behavior, while those with n of 6 and 7∼10 showed enantiotropic and monotropic nematic phases, respectively. In contrast, among the CAPETn polymers, only CAPET5 exhibited an enantiotropic nematic phase, while other polymers showed monotropic nematic phases. The isotropic-nematic transition temperatures of CAPETns and their entropy variation at the phase transition that were higher values than those of CAPBns, demonstrated a typical odd-even effect as a function of n. These phase transition behaviors were disscussed in terms of the 'virtual trimer model' by Imrie. The mesophase properties of CAPETns were largely different from those reported for the polymers in which the (cyanophenylazo)phenoxy groups are attached to polyacrylate, polymethacrylate, and polystyrene backbones through polymethylene spacers. The results indicate that the mode of chemical linkage of the side group with the main chain plays an important role in the formation, stabilization, and type of mesophase.

폴리(비닐 알코올)과 1-{4-(4′-시아노페닐아조)펜옥시}알킬브롬들(CAPBn, n=2∼10)을 이용하여 곁사 슬형 액정 동족체들인 폴리[1-{4-(4′-시아노페닐아조)펜옥시알킬옥시}에틸렌]들(CAPETn, n=2∼10, 유연격자 중의 메틸렌 단위들의 수)을 합성함과 동시에 이들의 열방성 액정 특성을 검토하였다. n=2~5인 CAPBn은 액정 상들을 형성하지 않는 반면 CAPB6 그리고 n=7∼10인 CAPBn들은 각각 쌍방성 그리고 단방성 네마틱 상들을 형성하였다. 이러한 사실과 판이하게, CAPETn 고분자들 중에서 CAPET5만이 쌍방성 네마틱 상을 형성하는 반면 나머지 고분자들은 단방성 네마틱 상들을 형성하였다. CAPETn들의 액체 상에서 네마틱 상으로의 전이온도들 그리고 CAPBn들에 비해 큰 값들을 갖는 CAPETn들의 상 전이시의 엔트로피 변화는 n의 함수로서 전형적인 홀수-짝수 효과를 나타냈다. 이러한 상 전이 거동들을 Imrie에 의한 'virtual trimer model'의 견지에서 검토하였다. CAPETn들의 액정 상의 특성들은 폴리아크릴레이트, 폴리메타크릴레이트 그리고 폴리스티렌에 (시아노페닐아조)펜옥시 그룹들을 폴리메틸렌 유연격자들을 통하여 연결시켜 얻은 고분자들에 대해 보고된 결과와 크게 달랐다. 이러한 결과들은 주사슬과 곁사슬 그룹의 화학적 결합양식이 액정 상의 형성능, 안정성 그리고 구조에 중요한 역할을 함을 시사한다.

Keywords: poly(vinyl alcohol); cyanoazobenzene; spacer length; nematic phase; ether linkage; odd-even effect.

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This Article

  • 2009; 33(4): 297-306

    Published online Jul 25, 2009

  • Received on Dec 17, 2008
  • Accepted on Jan 19, 2009