Soluble Polyimide Containing a Photoreactive 2‐Styrylpyridine Derivative as the Side Group: Synthesis and Characterization

Abstract

Summary: We describe the synthesis and characterization of a soluble photoreactive polyimide. The precursor of the polyimide was prepared from 2,2′‐bis{4‐(3,4‐dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride and 3,3′‐hydroxy‐4,4′‐diaminobiphenyl; the photoreactive polyimide was then prepared by the polymer reaction of the hydroxyl groups in the precursor polymer with 2‐{2‐[4‐(6‐hydroxyhexyloxy)phenyl]ethenyl}pyridine as a photoreactive 2‐styrylpyridine derivative. The photoreactive polymer and its precursor polymer were soluble in various polar organic solvents, and their thin flexible films were easily formed by solution casting. The initial decomposition temperatures of the former and latter polymers were 350 and 470 °C, respectively. The extent of the photochemical reaction of the photoreactive polymer film was measured to be 65.8% at an exposure energy of 1.5 J/cm2. The transmittance of the film was found to be approximately 92% at room temperature and approximately 85% at 200 °C. These results suggest that the polyimide is a photosensitive polymer with good photosensitivity and high optical transparency. The dichroic ratios of the film were between 0.023 and 0.025 when exposed to linearly polarized UV light (LPUVL). The liquid crystal in the film cell was perpendicularly oriented to the electric vector of LPUVL.

Liquid crystal photoalignment by a polymaleimide having a photoreactive 2-styrylpyridine derivative as aN-substituent

“…For reference, a polyimide with a 2-styrylpyridine moiety gave the decomposition temperature at 350 o C. 17 The DSC thermogram of polyPPDM did not show the melting point and the glass transition temperature, which indicates that the polymer has an amorphous structure.…”

“…5,14,17 The polymaleimide, polyPPDM, has three aromatic rings in the side group as given in Scheme I. However, the polyimides have four or six aromatic rings in the backbone units whereas only one or two aromatic rings in the side groups.…”

“…However, the polyimides have four or six aromatic rings in the backbone units whereas only one or two aromatic rings in the side groups. 5,14,17 The LC molecule has two aromatic rings. Considering the π-π interaction of aromatic rings for both the polymaleimide-LC and the polyimides-LC, the LC molecules will interact readily with the side group rather than the backbone unit of the polymaleimide, while those will actively interact with the backbone units of the polyimides rather than the side groups.…”

“…[1][2][3][4][5][6][7][8][9][10] In previous studies on the photoalignment of photosensitive polymers using linearly polarized ultraviolet (LPUV) light, polymers with azobenzene moieties as photoisomerizable groups 4 , polymers with cinnamoyl group, 11-15 styrylpyridine moieties 5,16,17 and coumarin moieties 1,18,19 as photocyclodimerizable groups, and deep UV light degradable polymers 20,21 have been mainly studied. Among these photosensitive polymers, polyimides with cinnamoyl group 14 or styrylpyridine moieties 5,17 in the side groups were reported to have thermal stability, thin film formation, and low energy LC photoalignment, etc. However, the structure and preparation of the backbone polymers are complex when compared to polymaleimides, and the photosensitive polyimides showed perpendicular LC photoalignment to LPUV light irradiation.…”

“…However, the structure and preparation of the backbone polymers are complex when compared to polymaleimides, and the photosensitive polyimides showed perpendicular LC photoalignment to LPUV light irradiation. 5,14,17 Polymaleimides have excellent thermal stability. Moreover, it was reported that polymaleimides with long alkyl groups on the nitrogen atom have a tough and thin film formation property.…”