含非常规侧链结构的液晶聚合物的合成及其超分子柱状相与柔性间隔基的关系

Synthesis of Liquid Crystalline Polymer Containing Unconventional Side Chain and the Effect of Flexible Spacer on Supramolecular Columnar Phase Formation

设计合成了一类具有非常规侧链结构的聚苯乙烯液晶聚合物PS-n(n=2,6,8,10,12),并研究了该类聚合物形成的超分子柱状液晶相与柔性间隔基之间的关系.所有聚合物表现出稳定的双向性液晶性质.当柔性间隔基较短(n≤6)时,聚合物形成超分子平行四边形柱状相(Colob)有序结构,该结构源于侧链中双液晶基元的取代位置引起的侧链层状堆积结构的周期性波动形成的二维有序堆积,且随着温度升高有序度有所增加.随着间隔基长度增加(n≥8),聚合物可形成2种不同晶胞参数的Colob相,其中在室温附近的Colob(I)相表现出波动层状相的特点,随着温度升高,聚合物进入有序度更高的Colob(Ⅱ)相,表现出高温组装的特殊性质.所有聚合物在继续升高温度后从Colob相进入层状相,最后进入各向同性相.由于柱子在聚合物薄膜内平行排列,PS-n薄膜表面可形成条纹状图案,在剪切力诱导下条纹图案可沿剪切方向发生宏观取向.

A class of polystyrene liquid crystalline polymer PS-n(n=2,6,8,10,12)with unconventional side chain structure was designed and synthesized.The influence of flexible spacer on the supramolecular columnar liquid crystalline phase formation was systematically studied.All polymers exhibit enantiotropic thermotropic liquid crystalline phase behaviour.When the flexible spacer is short(n≤6),the polymer forms a two-dimensional supramolecular ordered oblique columnar(Colob)phase structure,which results from the periodic fluctuation of the one-dimensional layered structure caused by the ortho substitution of two biphenyl mesogens per side chain.As the spacer length increases(n≥8),the polymer can exhibit two Colob phases with different lattice parameters at different temperatures.The Colob(I)phase with relatively small lattice parameter appeared near room temperature shows a characteristic undulated lamellar structure with oblique symmetry.With the increase of temperature,the polymer enters a higher ordered Colob(Ⅱ)phase with larger lattice parameter,showing the specific self-assembly behaviour at high temperature.When further increasing temperature,all polymers exhibit Colob to lamellar phase transition before entering isotropic state.The existence of long spacer length tends to promote the self-organization behaviour of side chain,which makes the appearance of highly ordered mesophase.Due to the parallel orientation of columnar structure,the fingerprint-like morphology can be found on the surface of thermal annealed PS-n thin film,and the macroscopic orientation can occur along the shear direction under shear induction.