Influence of Alkylene Spacer Length on Thermal Enhancement of Photoinduced Optical Anisotropy in Photo-Cross-Linkable Liquid Crystalline Polymeric Films and Their Composites with Non-Liquid-Crystalline Monomers

Abstract

Thermally enhanced photoinduced reorientation in a photo-cross-linkable liquid crystalline polymethacrylate comprised of 4-(ω-cinnamoyloxyalkyloxy)biphenyl side groups is investigated by irradiating with linearly polarized ultraviolet (LPUV) light and subsequent annealing at elevated temperatures. An odd−even effect of the alkylene spacer length between the cinnamate end group and biphenyl group on the transition temperatures of the polymer, photoinduced optical anisotropy, and thermal amplification of the in-plane molecular reorientation of thin films are observed. Because of the higher straight-line characteristics of the mesogenic side groups with an odd number alkylene spacer, the axis-selectivity of the anisotropic photoreaction of the photoreactive groups is greater than that with an even number, which leads to a larger photoinduced optical anisotropy and effective molecular reorientation. Finally, the cooperative reorientation in composites of the polymer and nonliquid crystalline monomer is explored to amplify the reorientational order of the film. The resultant reoriented composite film exhibits an in-plane order parameter of 0.52 and birefringence at 633 nm of 0.15.

Author reply

“…Monomers and PPLCs were synthesized according the procedure shown in Scheme . Monomers 1 , 2 , and 3 were synthesized according to the literature 15…”

“…We have conducted systematic studies on the photoinduced molecular reorientation in photo‐ cross ‐linkable polymer LC (PPLC) films containing mesogenic side groups terminated with cinnamate derivatives, which are transparent in the visible region 5, 9–11, 14–16. An efficient in‐plane molecular reorientation has been demonstrated in polymethacrylates with 4‐(4‐methoxy‐cinnamoyloxy)biphenyl (MCB) side groups [Fig.…”

“…To improve the solubility of the PPLC, an alkylene spacer has been introduced between the cinnamate end groups and biphenyl moiety [4‐(ω‐cinnamoyloxy‐alkyloxy)biphenyl (CB) side group, Fig. 1(b)], but the in‐plane molecular reorientational order of this type of PPLC is less than 0.3 14, 15. Furthermore, a high in‐plane molecular orientation with good photosensitivity has been observed in a polymethacrylate comprised of a hexamethylene spacer group terminated with a 4‐oxycinnamic acid (CA) [Fig.…”

Optimized molecular structures of guest–host system for highly efficient coatable polarizer

“…Studies on the host have focused on the monomer types of liquid crystals rather than the polymer types [7][8][9][10]. The monomer types, which usually form films by a photo curing method, have limitations in complete film formation and maintaining the alignment of molecules in the guest-host coatable polarizer [11][12][13]. In comparison, the polymer types are more advantageous to use in film formation because they involve a thermal curing method, which is a simpler method than photo curing.…”

Common diabetic therapy appears to reduce risk of pancreatic cancer

“…Among them, azobenzene or cinnamate polymers are able to generate films with high and stable photoinduced optical anisotropy based on axis‐selective photoreactions that occur on irradiation with linearly polarized (LP) light, a process that leads to a self‐organization in a preferred direction 7, 9–11. In some cases, the photoinduced anisotropy can be amplified significantly with subsequent thermal annealing in the mesophase 12–15. This effect has been observed not only in homopolymers but in copolymers with small percentages (10–20 mol %) of photoactive units 16–18…”