title: Sequence of Rubbing-Induced Molecular Segmental Reorientations in the Nanoscale Film Surface of a Brush Polymer Rod.
abstract: 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.
authors: 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.
authors: Boknam
authors: B
authors: Chae
authors: 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.
authors: Seung Woo
authors: SW
authors: Lee
authors: 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.
authors: Byeongdu
authors: B
authors: Lee
authors: 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.
authors: Wooyoung
authors: W
authors: Choi
authors: 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.
authors: Seung Bin
authors: SB
authors: Kim
authors: 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.
authors: Young Mee
authors: YM
authors: Jung
authors: 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.
authors: Jin Chul
authors: JC
authors: Jung
authors: 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.
authors: Kyung Hoon
authors: KH
authors: Lee
authors: 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.
authors: Moonhor
authors: M
authors: Ree