侧链密度对聚酰亚胺取向膜性能的影响

成功地合成了二胺单体十二烷氧基苯-4′,4″-二氨基三苯胺(DPDTA),并用此单体与3,3′-二甲基-4,4′-二氨基二苯甲烷(DMMDA)和二苯醚四羧酸二酐(ODPA)共缩聚,采用低温缩聚-热酰亚胺化、通过调节共聚物组成制备了2种聚酰亚胺(PI)。利用FT-IR、NMR、UV-Vis与DSC等手段对合成二胺单体及PI进行了结构表征和性能测试。研究了其取向性能、透光性能和耐热性能。结果表明,在摩擦前,含10%DPDTA的PI不能诱导液晶分子取向,含25%DPDTA的PI能诱导液晶分子垂直取向,预倾角可达89.6°。而摩擦后,两种PI都能使液晶分子平行取向,预倾角分别为1.8°和2.4°。两种PI膜在500～800nm区域透光率都在80%以上,玻璃化温度都在230℃以上。

Effect of Side Chain Density of Polyimides on Properties of Liquid Crystal Alignment Film

4-dodecyloxy-phenyl-4′,4″-diaminotriphenylamine (DPDTA) containing triphenylamine were successfully synthesized. Polyimides (PIs) containing triphenylamine units in the main chain were synthesized with the co-condensation of DMMDA, DPDTA and aromatic dianhydride 4 ,4′- oxydiphthalic anhydride (ODPA) by thermal imidization. The structures of the PIs were confirmed by FT-IR. The alignment behavior of PIs as liquid crystal alignment layers was also examined with polarized optical micrograph (POM). The properties of the PIs were characterized by TGA, UV-Vis and DSC etc. It was found that side chain density of PIs had important influence on properties of liquid crystal alignment film. Before rubbing, PI containing 25% DPDTA could induce uniform vertical alignment and a pretilt angle of 89.7°. The liquid crystal was not aligned on the surface of PI film which contained 10% DPDTA without the rubbing treatment. After the rubbing process, the pretilt angle of liquid crystal was 2.4, when PI film contained 25% DPDTA and the pretilt angle of liquid crystal was 1.8°, when PI contained 10% DPDTA. The transmittances of the PIs in 500~800 nm wavelengths are more than 80%, and their glass transition temperatures are above 230 ℃.