Side-chain liquid crystal copolymers(SCLCPs), which have a spirooxazine derivative(S) as a photochromic unit and a cyanobiphenyl derivative(M) as a mesogenic unit, were synthesized to study the possibility of optical memory storage applications. The synthesized spirooxazine and the mesogenic monomers were identified using mass spectrometry and elemental analysis. Random copolymers were synthesized using the following mole ratios of M to S : 100/0, 95/5, 90/10, 85/15, and 80/20. This was done by solution polymerization using 2,2'-azobisisobutyronitrile(AIBN) as an initiator and tetrahydrofuran as a solvent. The composition of the SCLCPs were determined by nuclear magnetic resonance spectroscopy(NMR), and the results showed the reactivity of the S was lower than that of the M. Synthesized SCLCPs showed liquid crystal behavior, which was identified by the differential scanning calorimetry(DSC) and the polarizing optical microscopy(POM). The DSC results showed a decrease of the smectic-to-isotropic transition temperature(T_SI) and the transition enthalpy(ΔH_SI) as the S content in the SCLCP increased. Moreover, at 8.4 mol% of S, the ΔH_SI was almost zero, indicating the disappearance of the liquid crystalline phase at this S content. This effect of S on the liquid crystalline phase was also supported by the POM results.

우수한 광 피로 저항성을 나타내는 spirooxazine을 광 변색성 단위(S), cyanobiphenyl을 mesogenic 단위(M)로 가지는 측쇄액정 고분자를 중합하여 광 저장 용도로의 사용 가능성에 대하여 연구하였다. 단량체들의 합성은 질량분석법, 원소분석법을 사용하여 확인하였으며, 불균일 공중합체는 AIBN을 개시제로 사용하여, THF에서 용액 중합하였다. 불균일 공중합체중의 S 및 M의 조성은 NMR을 사용하여 결정하였으며, S의 반응성이 M의 반응성 보다 낮음을 확인하였다. 중합된 공중합체의 상거동은 DSC 및 편광 현미경을 사용하여 확인하였으며, 공중합체중의 S의 함량이 증가할 수록, smectic→isotropic 전이 온도(T_SI) 및 엔탈피 (ΔH_SI)의 하강이 일어나고, S의 함량이 8.4 mol%에서 공중합체의 액정성이 거의 소멸됨을 관찰하였다. 편광 현미경 상에서는 S의 함량에 따른 texture의 변화가 3.8mol% 까지는 큰 변화가 없다가, 4.9mol% 부터 큰 변화가 나타났다.

Keywords: side-chain liquid crystal; optical storage; phase behavior