Synthesis and characterization of novel polyimides bearing a side chain composed of stilbene mesogen and undecyl spacer and the alignment ability of nematic liquid‐crystal molecules

Abstract

Four different polyimides with side chains containing undecyl spacers and 4-fluorostilbene mesogen end groups were prepared, and their structures and the controllability of the liquid-crystal (LC) alignment with rubbing were investigated. From X-ray scattering and differential scanning calorimetry data, pyromellitic dianhydride (PMDA)-, benzophenone-3,3Ј,4,4Ј-tetracarboxylic dianhydride (BTDA)-, and 4,4Јoxydi(phthalic anhydride) (ODPA)-based polyimides were shown to have layered structures and short-range ordering. Pretilt angles of LCs on the rubbed surfaces were 1-9°, depending on the rubbing density and backbone. In particular, the long undecyl spacers caused the mesogenic stilbene end groups to lie next to the main chain, resulting in a reduction in the pretilt angles.

High performance polyimides for applications in microelectronics and flat panel displays

“…[155][156][157][158][159] PIs are widely used as LC alignment layers because of their advantageous properties, such as excellent optical transparency, adhesion, heat resistance, dimensional stability and insulation. [65][66][67][68][69][70][71][72][73]95,124,125,155,156,[160][161][162][163][164][165][166][167] Such PI film surfaces need to be treated if they are to produce a uniform alignment of LC molecules with a defined range of pretilt angle values. [37][38][39][40][41][42]55,83,84,[108][109][110][111][112][113][114][115][116][117][118][119]…”

“…This process has become the method of choice because of its simplicity and the controllability with this method of both the LC anchoring energy and the pretilt angle. [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171] Much effort has been exerted to understand the mechanism behind the alignment of LC molecules on the rubbed polymer surface. A variety of factors have been proposed to explain the surface anchoring and alignment mechanism of the LC molecules: (i) microgrooves in connection with anisotropic LC orientational elasticity via steric interaction, [172][173][174][175][176][177][178] (ii) polymer molecules from the velvet fabric deposited and oriented on the alignment layer surface during the rubbing process, 179,180 (iii) surface electric fields, 181 (iv) anisotropically oriented polymer chains, [65][66][67][68]…”

“…A variety of factors have been proposed to explain the surface anchoring and alignment mechanism of the LC molecules: (i) microgrooves in connection with anisotropic LC orientational elasticity via steric interaction, [172][173][174][175][176][177][178] (ii) polymer molecules from the velvet fabric deposited and oriented on the alignment layer surface during the rubbing process, 179,180 (iii) surface electric fields, 181 (iv) anisotropically oriented polymer chains, [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171] (v) a near-surface order parameter different from the bulk LC molecules, 182,183 and (vi) coupling of a bending mode of the LC director to the surface electric fields (i.e., flexoelectricity). 184 Of these suggestions, the two models for the alignment process that have received the most attention are the microgroove mechanism …”

“…Some investigators have proposed that the outof-plane LC tilt angle is governed by van der Waals interactions between the LC molecules and the alkyl side chains of the polyimide. [65][66][67][68][69][70][71][72][73]95,124,125,[155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171]185 In contrast, other investigators have suggested that LC pretilt is determined by the polymer backbone structure but is independent of the length of the side chains. [186][187][188][189] The exact mechanism controlling the LC pretilt angle on rubbed surfaces has not yet been unambiguously elucidated.…”

Introduction of side chains containing biphenyl unit on the crystalline morphology and properties of polyimides

“…Kim et al 9 synthesized several polyimides with various side chains containing a biphenyl mesogen unit, and all the polyimide were apparently amorphous, but exhibited shortrange ordering to some extent. Park et al 10,11 synthesized different polyimide with side chains containing stilbene mesogen, and two interesting melting peaks were observed because of the melting of side chains and main chains, respectively. Ruan systematically explored the influence of the mesogens on the packing order and physical properties of the resulting polyimides.…”