Side-chain Liquid Crystalline Polyacetylenes Research Articles

Phase Behaviors of Side-Chain Liquid Crystalline Polyacetylenes with Different Length of Spacer: Where Will the Decoupling Effect Appear?

Phase structures and transitions of a series of biphenyl containing side-chain liquid crystalline polyacetylenes (SCLCPAs) with different length of spacer and alkyl tail, poly((m + 2)-{[(4′-alkyloxy-4-biphenylyl)carbonyl]oxy}-1-yne) [P-m,7 (m = 4, 5, 8), P-m,5 (m = 9), P-m,5L (m = 3, 9), m is the number of methylene units in the spacer], were studied by differential scanning calorimeter, polarized light microscopy, one- and two-dimensional wide-angle X-ray diffraction. It is revealed that phase structures of the samples are strongly dependent on the lengths of spacer and alkyl tail. The samples with short spacer (m ≤ 4) render the molecular shape of sheet-like due to the strong coupling between the backbone and the biphenyl groups on side-chains. They form highly ordered smectic phase with an additional ordering on the subnanometer scale (SmXo) at low temperatures. For m > 5, P-m,7 exhibits the low-temperature phase of smectic B (SmB), while P-9,5 and P-9,5L form smectic E (SmE). As the long spacers adopt...

Side-Chain Liquid Crystalline Polyacetylenes with Increasing Length of Alkyl Tails: From Highly Ordered Smectic to Smectic C Phase

Phase structures and transitions of a series of side-chain liquid crystalline polyacetylene (SCLCPA) with a short spacer of three methylene units and different lengths of alkyl tails, namely, poly(5-{[(4′-alkyl-4-biphenylyl)carbonyl]oxy}-1-pentyne) (P-3,m, m is the number of the carbon atoms in the alkyl tail, m = 5, 7, 9, 11), were investigated using differential scanning calorimeter, polarized light microscopy, and one- and two-dimensional wide-angle X-ray diffraction. With the short spacer, P-3,m possesses the mesogenic groups on the side chain and polyacetylene backbone coupled together and thus renders sheetlike shape with the width nearly twice of the extended side-chain length. Experimental results reveal that the liquid crystalline (LC) structure of P-3,m is strongly dependent on the side-chain tail length, different from that of other SCLCPAs. For m < 11, several layers of the sheetlike P-3,m molecules stack together to form a smectic A (SmA) block, and the number of molecular layers increases with increasing m. The adjacent SmA blocks slide halfway to each other, leading to a highly ordered smectic phase with frustrated molecular packing at low temperatures. The enantiotropic phase transition sequence of P-3,m (m < 11) follows: highly ordered smectic with additional ordering on the subnanometer scale ↔ highly ordered smectic ↔ semctic C (SmC) ↔ isotropic. However, when m is increased to 11, the packing of sheetlike P-3,11 gives the SmC phase, with the transition sequence of SmC with additional ordering on the subnanometer scale ↔ SmC ↔ isotropic. The phase structures of P-3,m were studied by computer modeling. The phase changing from the highly ordered one to SmC with increasing m may be ascribed to that the P-3,11 molecules intend to maximize the interaction between the biphenyl moieties in neighboring chains. We also investigated the orientation behavior of the highly ordered smectic phase under electric field, wherein a unique striplike texture was well developed, with the side chain and main chain parallel and perpendicular to the electric field, respectively.

Smectic Aggregates of Sheet-Like Side-Chain Liquid Crystalline Polyacetylenes Directly Formed During Solution Polymerization

We have successfully synthesized two side-chain liquid crystalline polyacetylenes (denoted as P3-5 and P2-5) with the mesogenic units based on a “phenyl−ester−phenyl” motif directly linked to the semirigid polyacetylene backbone in a terminal-on mode without flexible spacer. During the polymerization catalyzed by Rh(nbd)[B(C6H5)4] in toluene, the resultant polymers (or oligomers) automatically precipitate out of the polymerization solution as red solids, which cannot be dissolved in common organic solvents. Wide-angle X-ray diffraction results confirm that the polymer precipitates possess a smectic (or sanidic) structure, suggesting that the molecules without flexible spacers are sheet-like and can stack parallel to each other during polymerization. We in situ monitored the solution polymerization and the aggregation processes using UV−visible and 1H NMR spectroscopy methods. The experimental results indicate that after reaching a critical molecular weight the P3-5 and P2-5 molecules self-aggregate in sol...

Fluorescence Behavior of Biphenyl Containing Side-Chain Liquid Crystalline Polyacetylene with Various Lengths of Spacers

Steady state fluorescence and fluorescence decay of a series of monosubstituted biphenyl containing side-chain liquid crystalline polyacetylenes with different lengths of spacers were investigated. For comparison, a monomer was selected as a model compound. Steady state fluorescence spectra elucidated that the polymers and the monomer showed single fluorescence emission arising from the biphenyl group on the side chain. With decreasing the length of the spacer, the fluorescence intensity of the polymer decreased accordingly. The fluorescence decay showed that the decay of the monomer could be fitted to be a single-exponential decay, while that of the polymers should be fitted to be a triple-exponential decay, which may be originated from the local high concentration induced quenching and the rotational restriction of the side-chain biphenyl groups. Solvent effects illustrated that the interaction between the solvents and the biphenyl groups strengthened with increasing the polarity of the solvents.

Phase Transitions and Structures of 5-{[(4’-Pentyloxy-4-biphenylyl)carbonyl]oxy}-1-pentyne

Phase transitions and structures of the monomer of side-chain liquid crystalline polyacetylene containing biphenyl mesogen,namely,5-{[(4'-pentyloxy-4-biphenylyl)carbonyl]oxy}-1-pentyne (A3EO5) were investigated by differential scanning calorimetry (DSC),one dimensional (1D) wide angle X-ray diffraction (WAXD),and polarized light microscopy equipped with hot-stage (PLM-hot stage).DSC and 1D-WAXD results show that A3EO5 forms an enantiotropic liquid crystal and displays four transitions during the cooling and subsequent heating processes.Upon cooling from isotropic phase to room temperature,the sample forms smectic A phase and then leads to smectic B phase with pseudo long-range orientation within the layer structure,further lowering the temperature,A3EO5 forms smectic E phase with orthorhombic packing within the smectic layer and enters crystal phase.PLM results show that the sample forms spherulitic texture,focal conic texture and concentric arcs texture during the cooling process.

Shear induced molecular alignments of a side-chain liquid crystalline polyacetylene containing biphenyl mesogens

Mesomorphic properties of a side chain liquid crystalline polyacetylene, poly(11-{[(4′-heptyloxy-4-biphenylyl)carbonyl]oxy}-1-undecyne) (PA9EO7), are investigated using polarized optical microscope, X-ray diffraction, and transmission electron microscope. Polymer PA9EO7 forms enantiotropic smectic A and smectic B phases. It also exhibits an additional high order smectic phase, a sandwich structure consisting of different molecular packing of biphenyl mesogenic moieties from that of alkyl spacers and terminals, when it is prepared from its toluene solution. Shearing the polymer film at its smectic A phase generates banded texture with the alignment of the backbones parallel to the direction of shear force. While at its high order smectic phase, the mesogen pendants of the polymer are arranged parallel to the direction of shear. The different mesomorphic behaviors arise from different molecular alignments influenced by the fluidity.

Side Chain Liquid Crystalline Polyacetylene Derivatives. Synthesis and Properties.

Liquid crystalline (LC) polyacetylene derivative with a hexamethylene chain as a spacer in LC side chain was synthesized. The acetylene monomer substituted with LC group showed both nematic and smectic phases in the cooling process. The polymerizations of the monomers were carried out using Ziegler-Natta and metathesis catalysts. The polymers thus prepared showed smectic phases in heating and cooling processes, indicating an enantiotropic nature. We found that the mesophase of the present polymer is more stabilized with a longer methylene spacer.

Synthesis and Novel Mesomorphic Properties of the Side-Chain Liquid Crystalline Polyacetylenes Containing Phenyl Benzoate Mesogens with Cyano and Methoxy Tails

The synthesis of side-chain liquid crystalline polyacetylenes containing phenyl benzoate mesogens with octyl spacers and cyano (2a) or methoxy tails (2b) is accomplished, and the tuning of the molecular alignments of 2b is realized by simple mechanical perturbations. The acetylene monomers, 10-[4-(4‘-R-phenoxycarbonyl)phenoxycarbonyl]-1-decynes [R = cyano (1a), methoxy (1b)], are prepared by two consecutive esterification reactions of 10-undecynoic acid. None of the two monomers are liquid crystalline, but 1a exhibits an unusual crystal−crystal transition at 70.5 °C, probably due to its strong intermolecular ⋮C−H···N⋮C− hydrogen bonding. The polymerizations of 1 initiated by the WCl6−Ph4Sn/dioxane complex yield yellow powdery polymers (2) with Mw of ca. 30 000, whose molecular structures are characterized by NMR, IR, and UV spectroscopy. The mesomorphic behavior of 2 is investigated by DSC, POM, and XRD: 2a exhibits smecticity in a temperature range as wide as over 100 °C (k 80.4 sA 194.8 i), while 2b di...

Electrically Conducting Liquid Crystalline Polymers, Mono-Substituted Polyacetylene Derivatives

Abstract Novel side-chain liquid crystalline polyacetylene derivatives were synthesized by polymerizing substituted acetylene monomers with Ziegler-Natta and metathesis catalysts. Liquid crystallinities of the monomers and polymers were examined by means of miscibility tests, polarizing microscope and DSC measurements. Feasibility of iodine doping to the polymers was confirmed through UV-Vis absorption and ESR measurements. Changes of electronic and geometrical structures of the polymers upon the iodine doping were elucidated in terms of conjugation length of polyene chain, cis and trans forms, and spin distribution of unpaired electrons.

導電性液晶高分子

Recently we developed side chain liquid crystalline polyacetylene derivatives and achieved a substantial enhancement of electrical conductivity through magnetically forced alignment of the side chain of the polymer. When an electric field is employed as an alternative external force instead of the magnetic force, a ferroelectric liquid crystal should the more favorable than usual liquid crystals. This is because the former can respond more smoothly to the electric field owing to its spontaneous polarization than the latter. Here, in order to develop a novel liquid crystalline conducting polymer, we have synthesized a chiroptical liquid crystalline polyacetylene derivative. The liquid crystalline side chain of the polymer consists of a chiral alkyl moiety as a terminal group and a biphenyl moiety as a mesogenic core and a trimethylene segment as a spacer. The polymerization was carried out using a metathesis catalyst of MoCl{sub 5}-SnPh{sub 4}. Both the monomer and polymer showed the same signs in CD (circular dichroism) bands, indicating that the chirality of the monomer is maintained in the polymer. Measurements of DSC (differential scanning calorimeter) and polarizing microscope indicated that the polymer has a chiral smectic C (S{sub m} C*) phase assignable to the ferroelectric liquid crystal. Electrical and chemicalmore » properties of the polymer, including dielectric constant, electrical conductivity upon iodine doping and morphological alignment under an external force, are to be presented.« less