Combined Liquid Crystalline Polymers Research Articles

Main-chain side-chain combined liquid crystalline polymers bearing azobenzene and biphenyl-based mesogens – segregation of the mesogens within two distinct layers

ABSTRACT Two different mesogenic units, namely biphenyl and azobenzene, were installed centrally within the polymer backbone and pendant alkylene segments; the purpose was to examine if chain folding of the backbone occurs so as to segregate the azobenzene and biphenyl units in adjacent layers of a smectic-type ordering. Two sets of isomeric main-chain side-chain liquid crystalline polymers (MCSC-LCPs), namely SC-AzoCx-MC-BPCx and SC-BPCx-MC-AzoCx (x=6 or 10), were synthesised; the former series has biphenyl in the backbone and azobenzene in the side-chain, while their locations are switched in the latter. It was observed that all four polymers were semicrystalline at room temperature and exhibited a smectic mesophase upon melting. DSC and X-ray scattering studies revealed that switching the locations of the azobenzene and biphenyls had little effect on; the phase transition temperatures and smectic layer spacings. A second series, namely SC-AzoCx-MC-BPCy and SC-BPCx-MC-AzoCy, where the length of alkylene spacers in the side-chain (Cx) and backbone (Cy) is different, was also studied; this was done to examine the influence of unequal alkylene segment lengths on the mesophase structure and interlayer spacing, and importantly, whether the zigzag folding-induced formation of a layered structure is retained, despite their unsymmetrical nature.

Hierarchical Structures in a Main-Chain/Side-Chain Combined Liquid Crystalline Polymer with a Polynorbornene Backbone and Multi-Benzene Side-Chain Mesogens

A series of main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) with a polynorbornene backbone and multi-benzene mesogens in the side chain, PNbnPP (n = 2, 6, 10), were synthesized through a controllable polymerization method: ring-opening metathesis polymerization (ROMP). Differential scanning calorimetry, polarized light microscopy, and one-/two-dimensional wide-angle X-ray diffraction were utilized to investigate the phase behavior of PNbnPP. Experimental results reveal that the two fundamentally different liquid crystalline (LC) building blocks—the mesogen-jacketed LC polymer main chain and the multi-benzene calamitic mesogens in the side chain—compete and promote with each other, leading to a complex phase behavior. Because of the coupling effect between the rigid core and the pendants (multi-benzene mesogens) of PNb2PP with a short spacer, PNb2PP forms a simple smectic phase. On the other hand, owing to the decoupling effect of the long spacers, at low temperatures PNb6PP and PNb10PP form hierarchical structures, including the smectic phase of the polymer as a whole and the ordered packing of the multi-benzene mesogens.

Effects of main chain and acceptor content on phase behaviors of hydrogen-bonded main-chain/side-chain combined liquid crystalline polymers

Main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) are usually difficult to synthesize and their degrees of polymerization are relatively low, which bring difficulties in studying their structure–property relationships. In order to solve this problem, we prepared a new series of MCSCLCPs containing mesogen-jacketed liquid crystalline polymer (MJLCP) main chains via hydrogen-bonding (H–B). A pyridine derivative with a triphenylene (Tp) unit is the H–B acceptor. In addition to the temperature dependence, the phase behavior of the resulting complex is strongly influenced by the content of the H–B acceptor and the rigidity of the side-chain core of the MJLCP. The resulting complexes exhibit different phase structures: (1) a columnar nematic phase or a smectic A (SmA) phase formed by the supramolecular MJLCP chain as a whole; (2) hierarchical nanostructures including a hexagonal columnar phase or a SmA phase of the whole polymer chain plus a discotic nematic phase associated with the Tp moieties.

Ordered nanostructures at two different length scales mediated by temperature: A triphenylene‐containing mesogen‐jacketed liquid crystalline polymer with a long spacer

ABSTRACTA mesogen‐jacketed liquid crystalline polymer (MJLCP) containing triphenylene (Tp) moieties in the side chains with 12 methylene units as spacers (denoted as PP12V) was synthesized. Its liquid crystalline (LC) phase behavior was studied with a combination of solution 1H NMR, solid‐state NMR, gel permeation chromatography, thermogravimetric analysis, polarized light microscopy, differential scanning calorimetry, and one‐ and two‐dimensional wide‐angle X‐ray diffraction. By simply varying the temperature, two ordered nanostructures at sub‐10‐nm length scales originating from two LC building blocks were obtained in one polymer. The low‐temperature phase of the polymer is a hexagonal columnar phase (ΦH, a = 2.06 nm) self‐organized by Tp discotic mesogens. The high‐temperature phase is a nematic columnar phase with a larger dimension (a′ = 4.07 nm) developed by the rod‐like supramolecular mesogen—the MJLCP chain as a whole. A re‐entrant isotropic phase is found in the medium temperature range. Partially homeotropic alignment of the polymer can be achieved when treated with an electric field, with the polymer in the ΦH phase developed by the Tp moieties. The incorporation of Tp moieties through relatively long spacers (12 methylene units) disrupts the ordered packing of the MJLCP at low temperatures, which is the first case for main‐chain/side‐chain combined LC polymers with MJLCPs as the main‐chain LC building block to the best of our knowledge. The relationship of the molecular structure and the novel phase behavior of PP12V has implications in the design of LC polymers containing nanobuilding blocks toward constructing ordered nanostructures at different length scales. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 295–304

New Combined Liquid Crystalline Polymers from Polyaddition of Biphenol Diglycidyl Ether and Trimeric Esters

Six trimers with biphenyl mesogenic groups and polymethylene spacers were synthesized. From these trimers and biphenol diglycidyl ether (BPGE), a new series of combined liquid crystalline polymers (LCPs) with polyether backbone were synthesized by the polyaddition with quaternary phosphonium chloride as catalyst. The effects of flexible spacer length on the phase transition and mesomorphism of the resulting trimers and combined LCPs were studied using differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. The trimers with 1,3-propylene and 1,4-butylene spacers were absent of mesophase, and the trimers with odd-numbered spacers, 1,5-pentylene and 1,7-heptylene, were nematic. In contrast, the trimers with even-numbered spacers, 1,6-hexylene and 1,10-decylene, were smectic within very narrow temperature ranges. All the combined LCPs were thermotropically nematic, though the crystalline behavior was complex with varying side-chain spacer length. The combined LCPs ...

SAXS investigations on chiral liquid crystalline polymers: antiferroelectric and ferrielectric structures?

AbstractThe structure and phase behavior of liquid crystalline polymers (LCPs) having a common chiral side chain mesogen but different main chain structures have been investigated using small‐angle X‐ray scattering (SAXS). While the low molecular weight chiral side chain mesogen by itself exhibits ferroelectricity, the SAXS data of the side chain LCP with a flexible polyacrylate backbone contains a bilayered superstructure peak that is indicative of antiferroelectric order. The combined LCP with a nonpolar main chain mesogen also has a bilayered superstructure, but has a different structural organization in the proposed antiferroelectric phase compared to the side chain LCP. Further changes in the phase behavior and structural organization occur when a polar group is introduced into the main chain mesogen. A ferrielectric phase has been proposed to explain the observation of a trilayered superstructure in the corresponding SAXS data. The influence of the chemical structure and connectivity on the phase behavior and superstructure formation in the chiral LCPs is discussed.

X-ray investigation of combined main-chain/side-chain liquid-crystalline polymers

Abstract Structural investigations on six combined liquid-crystalline polymers using the X-ray technique are described. The measurements have allowed a characterization of the liquid-crystalline phases and have led to our first ideas about the phase structures. All mesogenic groups are arranged parallel to each other, the shortest segment in the main-chain or in the side-chain determines the smectic layer spacing. A modified designation for liquid-crystalline phases of high polymers is proposed.

New liquid-crystalline polymers with chiral phases

Abstract Liquid-crystalline polyesters with cholesteric and probably chiral smectic C∗ phases were prepared using combined liquid-crystalline polymers (that is polymers with the mesogenic groups in the main chain as well as in the side groups). Copolyesters of these polymers and polymers with olefinic double bonds could be cross-linked retaining the liquid-crystalline phases. This resulted in cross-linked polymers with elastic properties.

Structure‐property relations in linear and crosslinked liquid crystalline polymers

AbstractThis paper reviews structure‐property relations in liquid crystalline side group polymers, as investigated by X‐ray scattering of fibres, by small angle X‐ray scattering in solution, by dielectric relaxation measurements and by melt rheology, as well as synthetic ways to “combined liquid crystalline polymers”. The synthesis of liquid crystalline elastomers from side group, main chain and combined liquid crystalline polymers is described. First structure‐property relations are discussed.