Mesogen-jacketed Liquid Crystalline Polymers Research Articles

Design, Synthesis, and Characterization of Bent-Core Mesogen-Jacketed Liquid Crystalline Polymers

We report the design, synthesis, and characterization of a series of mesogen-jacketed liquid crystalline polymers with bent-core liquid crystals (BCLCs). For the first time, BCLC mesogens were directly side-attached to the polymer backbone and bent-core mesogen-jacketed liquid crystalline polymers (BMJLCPs) were achieved. Both three-ring and five-ring mesogens were employed. The n-alkoxy substituent lengths for the three-ring and five-ring BMJLCPs were controlled as n = 1−5 and n = 6−16, respectively. Various characterization techniques such as differential scanning calorimetry, wide-angle X-ray diffraction, and polarized light microscopy were used to study their mesomorphic phase behavior. The monomers of five-ring BMJLCPs with relatively long tails showed mesophase behavior. Columnar liquid crystalline phase was observed in both three-ring and five-ring BMJLCPs. Columnar rectangular (ΦR) phase was observed in the three-ring system. In the five-ring BMJLCPs, relatively short-tail homologues possess ΦR ph...

Synthesis and characterization of diblock copolymers based on crystallizable poly(ε-caprolactone) and mesogen-jacketed liquid crystalline polymer block

Diblock copolymers comprising crystallizable poly(ε-caprolactone) and poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene} (PMPCS) were synthesized by ring-opening polymerization of ε-caprolactone and subsequent atom transfer radical polymerization (ATRP) of MPCS. The molecular structure of the copolymers was confirmed by 1H NMR spectroscopy and GPC. Kinetic study of ATRP showed that the polymerization proceeded in a controlled way up to high conversions. Three series of diblock copolymers were obtained with relatively narrow polydispersity indices (PDI≤1.11) and PCL blocks of 8000, 12,900, and 22,800 molecular weights, respectively. The existence of microphase separation was identified by differential scanning calorimetry (DSC) and directly observed through transmission electron microscopy (TEM). The melting behavior of PCL block was significantly affected by the length of PCL block and composition of PMPCS. The thermotropic liquid crystalline behavior was examined by polarized optical microscopy (POM) and DSC. The result showed that the diblock copolymer exhibited liquid crystalline behavior when the degree of polymerization (DP) of PMPCS block was not less than 44.

Liquid-Crystalline Phase Development of a Mesogen-Jacketed PolymerApplication of Two-Dimensional Infrared Correlation Analysis

Two-dimensional correlation spectroscopy has been applied to study PMPCS (poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrene}), a representative example of mesogen-jacketed liquid crystalline polymers. With the precise analysis of a series of Fourier transform infrared (FTIR) spectra of PMPCS recorded at varied temperatures, a reasonable mechanism of the development of liquid crystalline (LC) phase is proposed. Before the phase transition, the conformational change of individual side chains occurs sooner than that of the backbone due to the larger motional freedom of the side chains. After the phase transition, however, the readjustment of still somewhat mobile backbone occurs before the ordered, rigid, and mutually interacting side chains. That is, phase transition leading to the LC phase formation brings in a new cooperative restriction of motions to the segments.

ABA Type Triblock Copolymer Based on Mesogen-Jacketed Liquid Crystalline Polymer: Design, Synthesis, and Potential as Thermoplastic Elastomer

We have designed and successfully prepared a well-defined ABA type triblock copolymer consisting of poly(n-butyl acrylate) as soft B block and poly{2,5-bis((4-methoxyphenyl)oxycarbonyl)styrene} (PMPCS) as hard A block with potential as liquid crystalline thermoplastic elastomer (LCTPE). The synthetic strategy is to obtain a difunctional poly(n-butyl acrylate) first and then use it as a macroinitiator for chain extension. Both steps employ atom transfer radical polymerization (ATRP). Kinetic study of the chain-extension polymerization demonstrates a well-controlled process. The resulted triblock copolymers have high molecular weights (Mn > 70 000) and low molecular weight distributions (Mw/Mn < 1.2). Their chemical structures are confirmed by nuclear magnetic resonance. Curves of differential scanning calorimetry indicate the immiscibility of the two components. Morphological investigations were made with transmission electrical microscopy and gave direct evidence of the existence of nanophase- separated structures with long-range order. After examinations by polarized optical microscopy, we found the triblock copolymers are LC only if the molecular weight of PMPCS block exceeds 20 000. Wide-angle X-ray diffraction measurements indicate a very stable nematic phase between glass transition of PMPCS block and decomposition. We found three samples are elastomeric. Preliminary mechanical tests were done on their films. Typical dynamic mechanical analysis and tensile tests prove that the sample has the potential as thermoplastic elastomers (TPEs). According to our best knowledge, the unique triblock copolymer is the first reported well-defined ABA type TPE imparting liquid crystallinity to the hard domains which serve as physical cross-links. Since the novel LC block copolymer has the rod-coil-rod conformation, it is also a new type of elastic rod-coil block copolymer.

Molecular Weight Dependence of Phase Structures and Transitions of Mesogen-Jacketed Liquid Crystalline Polymers Based on 2-Vinylterephthalic Acids

The phase structures and transition behaviors of a series of mesogen-jacketed liquid crystalline (LC) polymers, poly{2,5-bis[(4-methoxyphenyl)oxycarbonyl]styrenes} (PMPCS), with different molecular weights (MW) and narrow MW distributions were studied using differential scanning calorimetry, polarized light microscopy, Fourier transform infrared spectroscopy, and one- and two-dimensional wide-angle X-ray diffraction experiments. The LC phase structures of this series of PMPCS samples were found to be strongly MW dependent. The PMPCS samples were amorphous when the MW is lower than a critical MW of approximately 1.0 × 104 g/mol (an apparent MW, Mna, measured by gel permeation chromatography calibrated with the polystyrene standards). For the PMPCS samples with MWs higher than this critical value, the amorphous samples cast from solution developed into a LC phase above the glass transition temperature upon the first heating. In between 1.0 × 104 g/mol < Mna < 1.6 × 104 g/mol, a columnar nematic (ΦN) phase w...

Fluorinated mesogen-jacketed liquid-crystalline polymers as surface-modifying agents: Design, synthesis and characterization

Monomers with semifluorinated tails on monomeric vinyl hydroquinone cores were synthesized and their polymerization behavior was examined. The resulting semifluorinated mesogen-jacketed liquid-crystalline polymers (MJLCPs) proved to form fairly hydrophobic surfaces with water contact angles of 110–118°. These polymers were studied for the role of the fluorinated groups on both liquid-crystalline (LC) behavior and surface properties. Initial surface stability studies showed that these fluorinated MJLCP surfaces are relatively more stable than comparable systems of side-chain fluorocarbon LC blocks. Our studies show that M(1), 2,5-bis[(10-perfluorohexyl-decanoyl)oxy]styrene, could not be homopolymerized, while M(2) incorporating benzoate groups, 2,5-bis[4-(10-perfluorohexyl-decanyloxy)benzyloxy]styrene, permitted facile homopolymerization and block copolymer preparation by stable free-radical polymerization. As determined by wide-angle X-ray diffraction, the SCN transition temperature of the block copolymer shifted to a higher temperature with an increase in the DP of M(2). NEXAFS studies showed no net orientation of the (CF2)n side chains towards the surface normal consistent with observed low order smectic phases, nevertheless pointed to the presence of fairly hydrophobic CF2-covered surfaces. The above evidence proved the materials are suitable for application as surface-modifying agents. Polarized optical micrograph of M(1) showing a mosaic texture due to a smectic mesophase obtained on slow cooling at 2 K min−1 from the isotropic phase.

Characterization of mesogen-jacketed liquid crystalline polymers by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

For synthetic polymers, a proper sample preparation method is essential for successful characterization by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. In this work, six synthetic mesogen-jacketed liquid crystalline polymers (MJLCPs) with different main-chain, spacer and mesogenic units were investigated by MALDI-TOF mass spectrometry. Several factors that affect the analysis of these polymers were examined. These factors include matrices used, cationization salts used, the concentration of polymers, and the ratio of sample to matrix. After testing different conditions, we found a suitable sample preparation method for these six polymers. The number average molecular weight (M(n)), weight average molecular weight (M(w)) and polydispersity (PD) were calculated using data obtained in the linear mode. The end groups of the polymers were proposed using data obtained in reflectron mode. Copyright 2000 John Wiley & Sons, Ltd.

Mesogen-jacketed liquid crystalline polymer with flexible dicyclopentyl terephthalate as side group

For the first time the flexible cyclopentyl ring is used to build mesogenic units, and thus a novel mesogen-jacketed liquid crystalline polymer (MJLCP) poly(dicyclopentyl vinylterephthalate) is synthesized. The polymer forms a stable mesophase which changes to an isotropic phase at 267°C. The formation of a stable mesophase may be attributed to the spatial interaction among flexible side groups which converts them into rigid mesogenic units.

Mesogen-jacketed liquid crystalline polymers via stable free radical polymerization

Stable free radical polymerization has been used in the controlled synthesis of poly(2,5-bis[(4-butylbenzoyl)oxy]styrene), PBBOS. This “mesogen-jacketed liquid crystalline polymer”, which has mesogenic units attached directly to the backbone in a side-on mode, has been found to exhibit thermotropic liquid crystallinity similar to more conventional main-chain architectures. Stable free radical polymerization of PBBOS consistently produced molecular weight distributions below the theoretical limiting polydispersity of 1.5 calculated for a conventional free radical polymerization process. Surprisingly, a comparison of the synthesis of polystyrene to the polymerization of PBBOS under nearly identical conditions showed that the PBBOS polymerized with a significantly higher reaction rate and monomer conversion efficiency. The nematic phase of these polymers was determined to be stable over the temperature range spanning the polymer glass transition temperature up to the temperature for thermal decomposition. The molecular arrangement of the PBBOS polymers was examined by wide-angle X-ray diffraction and is described here.