Synthesis and Thermal Properties of Ferroelectric Side-Chain Liquid-Crystalline Polysiloxanes Based on Naphthyl Biphenylcarboxylate Mesogenic Groups and Oligooxyethylene Spacers

Abstract

In this work, three series of ferroelectric side-chain polysiloxanes containing oligooxyethylene spacers and (S)-2-methyl-1-butyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, (R)-1-methylheptyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates, and (2S,3S)-2-chloro-3-methylpentyl (2S)-2-[6-(4-hydroxybiphenyl-4‘-carbonyloxy)-2‘-naphthyl]propionates mesogenic groups were synthesized. The mesomorphic behaviors of three series of ferroelectric side-chain liquid-crystalline polysiloxanes were also studied using differential scanning calorimetry, optical polarizing microscopy, and high-resolution X-ray diffraction measurements. Some of these side-chain polysiloxanes containing four phenyl rings of ester cores (i.e., −Ph−Ph−COO−naphthyl−) and chiral heptyl tail present a smectic A (SA), and a chiral smectic C (Sc*) phase (around 100 °C). Another two series containing four phenyl rings of ester cores and chiral butyl and pentyl chain tail reveal a cholesteric (N*), an SA phase and an Sc* phase. The polymer PS12NC derivative with one unit of oxyethylene spacer (n = 1) of PSn2NC series reveals a N* phase, a twist grain boundary A (TGBA) phase, and a Sc* phase. X-ray investigations reveal that the packing of mesogenic groups for PS02NA, PS02NB, PS02NC with the shortest spacers (n = 0) exhibit a bilayer (two-layer) packing structures. Moreover, polymer PS32NA, PS32NB, PS32NC with the longest spacer chain (n = 3) reveal a monolayer packing structure. However, these two types of packing structure appear simultaneously in PS12NA (n = 1), PS12NC (n = 1), PS12NB (n = 1), and PS22NB (n = 2), depending on the chiral tail length. Results obtained in this study again demonstrate that the tendency toward chiral smectic C mesomorphism increases as the rigidity of phenyl ester mesogens increases via the flexible oligooxyethylene spacers system. Furthermore, the thermal stability of the chiral smectic C mesophase is determined by the flexibility of the chiral tail.

Liquid-crystalline ferroferric oxide nanocomposites: self-assembly and magnetorheological effects

“…In the XRD curves, all the Fe 3 O 4 @PILCs and the corresponding precursor polymers show separately a sharp reflection (2y o 41) associated with the smectic layers at small angles and a broadly dispersed reflection at wide angles (2y B 181) associated with the lateral packings, suggesting the SmA phase. 34 311), (400), (511), and (440) planes, respectively. 35 Moreover, both Fe 3 O 4 @PILC-1 and PILC-1 show diffuse peaks around 2y B 181 which are attributed to the lateral packing polymer structures.…”

“…In the XRD curves, all the Fe 3 O 4 @PILCs and the corresponding precursor polymers show separately a sharp reflection (2 θ < 4°) associated with the smectic layers at small angles and a broadly dispersed reflection at wide angles (2 θ ∼ 18°) associated with the lateral packings, suggesting the SmA phase. 34 Fig. 4e shows the XRD patterns of a representative nanocomposite sample (Fe 3 O 4 @PILC-1) along with bare Fe 3 O 4 and the precursor LC polymer PILC-1 at 200 °C.…”

Polysiloxane-Based Side Chain Liquid Crystal Polymers: From Synthesis to Structure–Phase Transition Behavior Relationships

“…Special attention is paid to the effect of the heteroatom (such as O, S) in the spacers and their properties. In regard to the dependence of mesogenic units on phase structures and phase behaviors, in addition to the influence of diverse rigid structures [76,77,78]; the lateral substituents of the mesogenic side groups [79,80,81], the aliphatic tail length of the mesogenic groups [82,83,84,85], the chirality [86,87,88,89] and polarity [90] of the mesogenic groups, and the functionality of the mesogenic groups (such as photo-sensitive property [91,92,93,94], amphiphilic property [95,96], etc.) exerted a strong effect on mesomorphic properties.…”