Smectic C Self‐Assembly in Mesogen‐Free Liquid Crystalline Chiral Polyethers with Sulfonylated Methyl‐Branched Side Chains

• Published in: Macromolecular rapid communications. 2023-01, Vol.44 (1), p.e2200501-n/a
• Main Authors: Bohannon, Caleb A., Kwok, Man‐Hin, Huang, Jiahao, Rui, Guanchun, Li, Ruipeng, Zhu, Lei, Zhao, Bin
• Format: Article
• Language: English
• Subjects: Chain branching; Chirality; Dipole interactions; dipole–dipole interaction; Electric fields; Ferroelectric materials; Ferroelectricity; isotactic polyethers; Liquid crystal polymers; Liquid crystals; mesogen‐free liquid crystalline polymers; Polyethers; Polymers; Polymers - chemistry; Polystyrene resins; smectic C phase; sulfonylated side chains; Switching
• ISSN: 1022-1336; 1521-3927
• DOI: 10.1002/marc.202200501

To realize advanced electrical applications for ferroelectric liquid crystalline polymers, high spontaneous polarization (Ps) is highly desired. However, current ferroelectric liquid crystalline polymers usually exhibit a low Ps. In this work, mesogen‐free, chiral polyethers containing sulfonylated methyl‐branched alkyl side chains with a (CH2)3O spacer between the sulfonyl and the branched alkyl groups are designed and synthesized. In contrast to the linear n‐alkyl side chains, the methyl‐branched alkyl side chains induce chain tilting in the smectic layers. When double chirality exists in both the main chain and the side chains, a crystalline structure is observed after mechanical stretching. Intriguingly, when single chirality exists in either the backbone or the side chains, a liquid crystalline smectic C phase is obtained. The electric displacement–electric field study, however, does not show typical ferroelectric switching, although the dielectric constants are relatively high for these liquid crystalline polymers. This is likely because the dipole–dipole interactions among neighboring sulfonyl groups along the main chain are so strong that the ferroelectric switching is hindered in the samples. For the future work, it is desired to weaken the dipole–dipole interaction to achieve ferroelectricity in these mesogen‐free liquid crystalline polymers. Smectic C self‐assembly is achieved for the first time in mesogen‐free liquid crystalline chiral polymers with sulfonylated methyl‐branched alkyl side chains, as revealed by X‐ray diffraction and polarized light microscopy. These polymers exhibit high dielectric constants between 7.9 and 11.7.