Chae Boknam, Lee Seung Woo, Lee Byeongdu, Choi Wooyoung, Kim Seung Bin, Jung Young Mee, Jung Jin Chul, Lee Kyung Hoon, Ree Moonhor
Department of Chemistry, BK21 Program, Division of Molecular and Life Sciences, Center for Integrated Molecular Systems, Polymer Research Institute, and Department of Materials Science & Engineering and Center for Advanced Functional Polymers, Pohang University of Science & Technology, San 31, Hyoja-dong, Pohang 790-784, Republic of Korea.
J Phys Chem B. 2003 Oct 30;107(43):11911-6. doi: 10.1021/jp034955q.
Poly(p-phenylene-3,6-bis(4-(n-butoxy)phenyloxy)pyromellitimide) (C4-PMDA-PDA PI), a well-defined model brush polymer composed of a rodlike polymer backbone with two bristles per repeat unit, was the first reported polyimide to align liquid crystals perpendicular to the rubbing direction at the rubbed film surface. In the present study, we used polarized infrared (IR) spectroscopy and 2D correlation analyses of the resulting IR spectra to study nanoscale films of C4-PMDA-PDA PI rubbed at various rubbing densities. The results of these studies allowed us to establish the nature and sequence of the rubbing-induced segmental reorientations that occur in the polymer molecules at the film surface. The rubbing process was found to reorient the fully rodlike polymer backbones and the n-butyl bristle end groups such that they lay parallel to the rubbing direction. In contrast, rubbing caused the phenyloxy bristle units to reorient to a direction perpendicular to the rubbing direction. These reorientations of the polymer's main chain and bristles became more pronounced with increasing rubbing density, and the rubbing process had a greater effect on the polymer's main chains than on the bristles. The rubbing-induced reorientations of the polymer segments were found to follow the sequence PDA (phenyl ring), imide ring, phenyloxy unit, imide C-N bond, and n-butyl group. It was additionally evident that the rubbing process reorients the imide rings biaxially, that is, both along the rubbing direction and out of the plane. This biaxial reorientation was found to be accompanied by a biaxial reorientation of the bristles chemically bonded to the PMDA unit that includes the imide rings. In particular, increasing the rubbing density enhanced the out-of-plane reorientation of the imide rings. In contrast, no rubbing-induced inclination of the reoriented imide rings (i.e., the polymer's main chains) was detected.
聚（对亚苯基-3,6-双（4-（正丁氧基）苯氧基）均苯四酸二酰亚胺）（C4-PMDA-PDA PI）是一种结构明确的模型刷状聚合物，由棒状聚合物主链组成，每个重复单元有两个刷毛，是首个被报道的能使液晶在摩擦薄膜表面垂直于摩擦方向排列的聚酰亚胺。在本研究中，我们使用偏振红外（IR）光谱以及所得红外光谱的二维相关分析来研究在不同摩擦密度下摩擦的C4-PMDA-PDA PI纳米级薄膜。这些研究结果使我们能够确定在薄膜表面聚合物分子中发生的摩擦诱导链段重排的性质和顺序。发现摩擦过程会使完全呈棒状的聚合物主链和正丁基刷毛端基重新取向，使其与摩擦方向平行。相比之下，摩擦使苯氧基刷毛单元重新取向至垂直于摩擦方向的方向。随着摩擦密度的增加，聚合物主链和刷毛的这些重排变得更加明显，并且摩擦过程对聚合物主链的影响比对刷毛的影响更大。发现聚合物链段的摩擦诱导重排顺序为PDA（苯环）、酰亚胺环、苯氧基单元、酰亚胺C-N键和正丁基。此外还明显看出，摩擦过程使酰亚胺环发生双轴重排，即既沿摩擦方向又垂直于平面方向。发现这种双轴重排伴随着与包含酰亚胺环的PMDA单元化学键合的刷毛的双轴重排。特别是，增加摩擦密度增强了酰亚胺环的垂直于平面方向的重排。相比之下，未检测到摩擦诱导的重排酰亚胺环（即聚合物主链）的倾斜。
