聚酰亚胺主链结构对液晶取向膜性能的影响

采用一步法,以N,N-二(4-氨基苯基)-4-(十二烷氧基联苯基)-4’-氨基苯醚(C12-BAAPE)为控制预倾角的功能性二胺,2,2’-双三氟甲基-4,4’-联苯二胺(TFDB)或4,4’-二氨基二苯醚(ODA)为辅助二胺,分别与2,2’-双(3,4-二羧苯基)六氟丙烷四羧酸二酐(6FDA)和4,4’-联苯醚二酐(ODPA)聚合,得到三种主链结构不同的聚酰亚胺(PI-1、PI-2和PI-3)。利用NMR、FT-IR、DSC、TGA、偏光显微镜和预倾角测试仪对聚合物的结构、热性能以及制备的液晶盒的取向性进行了表征,同时测试了3种PI的溶解性能。结果表明,PI-2液晶取向膜的耐摩擦性能明显优于PI-1和PI-3,且具有更高的玻璃化转变温度(Tg)和分解温度(Td),更好的溶解性能。分子模拟(MS)表明,由于PI-2分子主链垂直构象的存在,增加了分子链的刚性,因而提高了取向膜的耐摩擦性能。

Properties of polyimide liquid crystal alignment layer with different backbone structure

A series polyimides (PIs) were prepared by one-step method. These PIs were comprised of a functional diamine N,N-bis(4-aminophenyl)-4-(dodecylo-xy-biphenyl)-4'-amino-phenylether (C₁₂-BAAPE), one of two commercially available diamines 2,2'-Bis(trifluoromethy-l)-4,4'-diaminobiphenyl (TFDB), 4,4'-Oxydianiline (ODA) and one of two dianhydride 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 4,4'-Oxydiphthalic anhydride (ODPA) in order to get different backbone structures. The structures and thermo properties of these PIs were characterized by NMR, FT-IR, DSC and TGA. Pretilt angles and alignment abilities were carried out by pretilt angle tester and polarization microscope. Solubility of PIs was tested by dissolving PIs in various organic solvents. DSC and TGA curves showed that PI-2 had higher glass transition temperature (T_g) and decomposition temperature (T_d) than PI-1 and PI-3. Three PI films presented vertical alignment before mechanical rubbing and only PI-2 maintained it after rubbing process. Conformations of these PIs were simulated by Material Studio (MS). The vertical conformation existed in PI-2's backbones improved rubbing resistance and showed vertical alignment ability after rubbing.