掺杂光敏分子对环氧树脂光定向材料的性能影响

分别将肉桂酸和对正辛氧基肉桂酸进行酰氯化,与环氧树脂先驱聚合物(BP-AN)发生官能化反应,合成以肉桂酸酯和对正辛氧基肉桂酸酯为侧基的两种感光高分子(BP-AN-H和BP-AN-C8),然后合成了两种感光分子,对苯二酚双肉桂酸酯和对苯二酚双对正辛氧基肉桂酸酯,利用1H-NMR、FTIR进行了表征.最后将对应感光高分子与感光分子按不同比例掺杂,利用线性偏振光聚合(LPP)技术制备光定向层,组装成液晶盒.在偏光显微镜下观察液晶盒的定向效果,并测定其透过率-旋转角曲线.发现在一定的掺杂比例以下,增大掺杂感光分子的比例能够提高体系的定向效果,而且掺杂对苯二酚双对正辛氧基肉桂酸酯对定向能力的提高效果更为明显.

The effect of doping photo-sensitive molecules on the properties of epoxy-resin based photo-alignment materials

Epoxy-based photosensitive polymers with two different cinnamoyl side groups (cinnamoyl group and 4-octyloxy cinnamoyl group) were prepared by functionalization of the polymer precursor (BP-AN).Two kinds of photo-sensitive molecules including cinnamoyl groups were also prepared:hydroquinone dicinnamate obtained by reaction between hydroquinone and cinnamoyl chloride,while hydroquinone di(4-octyloxyl)cinnamate synthesized through reaction between hydroquinone and 4-octyloxy cinnamoyl chloride.All chemicals were characterized by necessary spectroscopic methods including ~1H-NMR and FTIR,which indicated their accurate molecular structures had matched our target molecules.The photo-sensitive molecules were doped into corresponding photo-sensitive polymers in different proportions respectively,and photo-alignment layers were prepared based on the spin-coated films of the polymers,which were irradiated under LPUV (linearly polarized ultra violet) and then used to assemble LC cells filled with nematic liquid crystal 5CB.The photo-alignment behavior of the doped polymers was characterized by the microscopic observation and comparing the numerical value of T_ max /T_ min in sinusoid-curves of LC cells.The results showed that,below a certain doping point (about 10%),increasing the concentration of the photo-sensitive molecules would result in a better photo-alignment performance.Since the photo-dimerization reaction of cinnamoyl groups happens only when two cinnamoyl groups stand in properly spatial positions to form a tetra-atomic ring.Doped molecules greatly added up the amount of cinnamoyl pairs with adequate steric relations,thus created greater chance for cinnamoyl groups to crosslink and improved the LC-alignment performance.By doping different amount of photo-sensitive molecules we found the ideal doping point would be around 10%(n_p∶n_m).Doping content going up higher than that would lead to a worse alignment effect,with the presence of irregular patterns and luminous points under light microscope,and decreased contrast too.Luminous points were probably caused by the limited compatibility between the polymer and the doped molecules,and doped photo-sensitive molecules cumulated and became crystallized.As for irregular patterns,they are surely caused by the weak photo-alignment ability of the doped polymer.On one hand,tiny crystals would disturb the uniformity of the surface;on the other hand,it is possible that the existence of excess amount of cinnamoyl groups would both enhance photo-dimerization and photo-isomerization reactions,which are competitive reactions and lead to opposite alignment directions:photo-dimerization would align the LC molecules parallel to the polarization direction of LPUV,while photo-isomerization would align them perpendicular to the polarization direction of LPUV.At the same time,we found that LC cells doped with 4-octyloxy cinnamoyl groups showed a higher increase in photo-alignment performance,which indicated that the effect of doping varied for different systems,and this method could be rather useful for certain polymers.In a word,we've synthesized two novel photo-sensitive molecules and doped them into epoxy polymers to enhance the alignment ability of the material with success.In our case,the contrast could be doubled or even tripled by doping adequate amount of photo-sensitive molecules.The optimum doping amount found is around 10%,regardless of the assortments of epoxy polymers.