Thermotropic liquid crystalline polymers. II. Polymers with amino acid fragments in the side chains

The comblike polymers, poly(N^ε-methacryloyl-N^α-acyl) derivatives of L -lysine, which contain amino acid fragments and long sequences of methylene groups in the side chain, were synthesized. This article, which is based on x-ray data, differential thermal analysis, and optical microscopy, describes the structure of these polymers and their properties. It also shows that the combination of anisodiametric side groups with a “rigid” matrix of main chains leads to a liquid crystalline structure of examined polymers.     

Liquid crystalline conjugated polymers and their applications in organic electronics

This article describes the syntheses and electro‐optical applications of liquid crystalline (LC) conjugated polymers, for example, poly(p‐phenylenevinylene), polyfluorene, polythiophene, and other conjugated polymers. The polymerization involves several mechanisms: the Gilch route, Heck coupling, or Knoevenagel condensation for poly(p‐phenylenevinylene)s, the Suzuki‐ or Yamamoto‐coupling reaction for polyfluorenes, and miscellaneous coupling reactions for other conjugated polymers. These LC conjugated polymers are classified into two types: conjugated main chain polymers with long alkyl side chains, namely main‐chain type LC polymers, and conjugated polymers grafting with mesogenic side groups, namely side‐chain type LC conjugated polymers. In general, the former shows higher transition temperature and only nematic phase; the latter possesses lower transition temperature and more mesophases, for example, smectic and nematic phases, depending on the structure of mesogenic side chains. The fully conjugated main chain promises them as good candidates for polarized electroluminescent or field‐effect devices. The polarized emission can be obtained by surface rubbing or thermal annealing in liquid crystalline phase, with maximum dichroic ratio more than 20. In addition, conjugated oligomers with LC properties are also included and discussed in this article. Several oligo‐fluorene derivatives show outstanding polarized emission properties and potential use in LCD backlight application. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2713–2733, 2009     

Structure of crystalline polymers with unbranched long side chains

The structure and thermodynamic properties of atactic and isotactic acrylic and methacrylic polymers containing 16–18 carbon atoms in the n-aliphatic side chains, and of copolymers of hexadecyl acrylate with isopropyl acrylate were studied by means of x-ray and differential thermal analysis. The crystallization of branched acrylic and methacrylic polymers and of acrylic copolymers proceeds in the form of a hexagonal crystal, regardless of the configuration of the backbone chain. Methods of ordering branched macromolecules are proposed, and the melting points, heats and entropies of fusion determined. The role of flexibility of the backbone chains in ordering and the crystallization processes was determined. In the case of poly(n-alkyl acrylates) the backbone chain is involved in the crystalline lattice; this is not the case in methacrylates and copolymers of hexadecyl acrylate with isopropyl acrylate. Some similarity was assumed between the structure of biopolymers and synthetic branched polymers.     

Effect of molecular structure on mesomorphism XXI. Monodisperse tetrameric model compounds for liquid crystalline polymers

Abstract

Twinned dimeric mesogens having a rigid-flexible-rigid molecular structure have been shown to be appropriate models for some properties of regularly alternating (rigid-flexible)_n main chain liquid crystalline polymers (lcps). A family of tetrameric monodisperse liquid crystalline model compounds chemically related to known main chain liquid crystalline polymers of the 4-alkoxyphenyl 4′-alkoxy-benzoate type has been synthesized. The tetramers are nematogenic. Alternations in thermodynamic parameters (ΔH, ΔS) for the N-I transition as a function of spacer chain length indicate conformational behaviour of the internal spacers dominates mesophase properties.     

Side chain type ionic liquid crystalline polymers having high Preliminary communication molecular weight

Side chain type ionic liquid crystalline polymers having a 4-(1,3-dioxan-2-yl)pyridinium structure in their mesogenic side chain were synthesized. These polymers exhibited the smectic A phase. The molecular weights of these ionic liquid crystalline polymers are very high, e.g. for compound 7 - 2 M _w = 486 000.     

Influence of alkoxy tail length and unbalanced mesogenic core on phase behavior of mesogen‐jacketed liquid crystalline polymers

When the flexible terminal substituent changes from butoxy to hexyloxy or longer, smectic C (S_C) liquid crystalline phase was firstly reported to develop from a kind of mesogen‐jacketed liquid crystalline polymer (MJLCP) whose mesogenic side groups are unbalancedly bonded to the main chain without spacers. A series of MJLCPs, poly[4,4′‐bis(4‐alkoxyphenyl)‐2‐vinylbiphenyl(carboxide)] (nC2Vp, n is the number of the carbons in the alkoxy groups, n = 2, 4, 6, 8, 10, and 12) were designed and synthesized successfully via free radical polymerization. The molecular weights of the polymers were characterized with gel permeation chromatography, and the liquid crystalline properties were investigated by differential scanning calorimetry, polarized light microscopy experiments, and 1D, 2D wide‐angle X‐ray diffraction. Comparing with the butoxy analog, the polymer with unbalanced mesogenic core and shorter flexible substituents (n = 2, 4) keeps the same smectic A (S_A) phase, but other polymers with longer terminal flexible substituents (n = 6, 8, 10, and 12) can develop into a well‐defined S_C phase instead of S_A phase. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 505–514, 2009     

Compatibility of coils and rods bearing flexible side chains

We present a theoretical treatment of nematic-isotropic phase equilibria in mixtures which consist of random coils and comblike polymers, the latter components being composed of a rigid backbone and flexible side chains. The mixing partition function is evaluated by using the Flory lattice model. The comblike component is characterized by the axial ratio x_r of its rigid main chain and the number of flexible side chains z, each containing m segments. The coiled component is described by its number of segments x_c. The net exchange energy of mixing is assumed to be zero; i.e., we consider athermal solutions. It is shown that the flexible side chains attached to the rigid main chains markedly enhance the compatibility in the isotropic phase. If the ratio of the volume fraction of the side chains to the volume fraction of the main chains is high enough, there is even a finite range of concentration where the random coils mix homogeneously with the comblike component. This is in contrast to mixtures of rods and coils, which have been shown by Flory to be incompatible over nearly the full range of composition. These conclusions hold true only when ordered states are involved. For comblike polymers with flexible backbones mixed with random coils in isotropic melts, the resulting free energy of mixing is given by the familiar Flory-Huggins expression.     

Influencing factors on liquid crystalline properties of cholesterol side-chain liquid crystalline polymers without spacer: molecular weight and copolymerisation

ABSTRACT

It is a challenge to tailor the phase behavior and phase structure of side-chain liquid crystalline polymers carrying targeted ordered structures and functional properties. In this work, liquid crystalline (LC) properties of cholesterol side-chain polymers without spacer were controlled by molecular weight (M_n) and copolymerization. On the one hand, two series of homopolymers without the spacer, poly (methacrylic acid) cholesterol esters (PCholMC_n) and poly (acrylic acid) cholesterol esters (PCholAC_n) with different M_n and low polydispersity, were achieved by reversible addition-fragmentation chain transfer polymerization. The experiment results indicated that the M_n had little effect on the LC properties of PCholMC_n and all homopolymers formed the smectic A phase. However, the phase structures of PCholAC were found to be strongly M_n dependent. The polymers PCholAC_n were amorphous when the M_n was lower than a critical value of approximately 1210₃ g/mol. But when the M_n exceeded the critical value, the polymers exhibited smectic A phase. On the other hand, two kinds of random copolymers, poly(cholest-5-en-3-methacrylate)-co-polymethyl acrylate (PCholMC-co-MA) and poly(cholest-5-en-3-acrylate)-co-polymethyl acrylate (PCholAC-co-MA) were synthesized with various composition. The findings suggested that the steric effect of main-chain and the interaction of mesogens would promote the formation of LC phase.     

Salt effects on cloud points and viscosities of polymethacrylates with pendant oligo-oxyethylene chains

Comblike polymethacrylates with oligo-oxyethylene side chains were synthesized from the commercially available monomers CH₂ ? C (CH₃) COO (CH₂CH₂O)_nCH ₃, the average n being 4, 8, and 22. The three polymers exhibited lower critical solution temperatures in aqueous media. Cloud points were determined as a function of the nature and concentration of salt. For salts that destabilize the polymer solutions, the cloud points decrease linearly with salt concentration, the extent of the decrease being strongly anion dependent. Salt effects on the viscosity of the polymers were measured in water, methanol, and acetonitrile. In water the viscosity decreases on adding salt, but in methanol and acetonitrile the neutral polymers are converted to polycations as cations form stable adducts with the oligo-oxyethylene side chains. The increase in viscosity is both cation and anion dependent. The general behavior of the comblike polymers resembles that reported for aqueous or methanolic salt solutions of poly (ethylene oxide) and nonionic surfactants.     

Crosslinked liquid crystal polymers from liquid crystal monomers: Synthesis and mechanical properties

Difunctional acrylates and methacrylate monomers have been made which are high order smectic liquid crystal (or crystalline) at room temperature. This report discusses materials with the following structure: F–S–M–S–F, where F is a functional group, acrylate or methacrylate (A or M); S is a spacer (CH₂)_n(n), and M is a mesogen—in this case 4,4′-dioxybiphenyl (B). They are codified as BnA or BnM where n is the number of methylenes in the spacer. High conversion with high T_g can be obtained when polymerizing in the smectic state because the reactive end groups are concentrated in a small volume and can react well with little or no diffusion. B2A, B3A, B6A, B11A, and B3M were polymerized in the smectic state and compared to polymers made at temperatures where the monomers were isotropic. High conversion was obtained below final T_g—even then, probably because the polymers were ordered. All the polymers were studied by WAXD and dynamic mechanical spectroscopy. Solid-state NMR on B3A showed that there was very high conversion of the double bonds at all temperatures. B3A photopolymerized in the smectic state (60–76°C) produced a crystalline polymer with T_g = 185°C (1 Hz). When photopolymerized at 85°C, above the isotropization temperature (T_i), a poorly organized polymer was obtained with a T_g of 155°C (1 Hz). Monomers with an odd number of methylene groups as spacers were crystalline after polymerization. With an even number of methylene groups, they lost most of their crystallinity on polymerization below T_i, but retained a low order smectic structure. Similar structures were obtained with all the monomers when they were polymerized above T_i. There was little effect of polymerization temperature on T_g when the spacers had an even number of methylene groups. © 1993 John Wiley & Sons, Inc.     

High‐molecular‐weight side‐chain liquid‐crystalline polyethers based on 4′‐cyanobiphenyl‐4‐oxy mesogenic groups

A set of poly[ω‐(4′‐cyano‐4‐biphenyloxy)alkyl‐1‐glycidylether]s were synthesized by the chemical modification of the corresponding poly(ω‐bromoalkyl‐1‐glycidylether)s with the sodium salt of 4‐cyano‐4′‐hydroxybiphenyl. New high‐molecular‐weight side‐chain liquid‐crystalline polymers were obtained with excellent yield and almost quantitative degree of modification. All side‐chain liquid‐crystalline polymers were rubbers soluble in tetrahydrofuran. The characterization by ¹H and ¹³C NMR revealed no changes in the regioregular isotactic microstructure of the starting polymer and the absence of undesirable side reactions such as deshydrobromination. The liquid crystalline behavior was analyzed by DSC and polarized optical microscopy, and mesophase assignments were confirmed by X‐ray diffraction. Polymers that had alkyl spacers with n = 2 and 4 were nematic, those that had spacers with n = 6 and 8 were nematic cybotactic, and those that had longer spacers (n = 10 and 12) were smectic C and showed some crystallization of the side alkyl chains. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3002–3012, 2004     

Amphiphilic mesogen‐jacketed liquid crystalline polymers: Design,synthesis, and self‐assembly behaviors

We synthesized a series of amphiphilic mesogen‐jacketed liquid crystalline (LC) polymers with a biphenyl side‐chain mesogen containing a carboxylic acid group on one side and an octyloxy group on the other, and the number of methylene units between the biphenyl core and the exterior carboxylic acid group was varied to adjust the mesophases and the amphiphilic nature. The polymers were obtained through conventional radical polymerizations and characterized by a combination of different techniques such as thermogravimetric analysis, differential scanning calorimetry, polarized light microscopy, and X‐ray scattering. The results revealed that the polymer without any methylene spacer, POBP‐0C, did not exhibit LC properties while POBP‐1C (n = 1) and POBP‐7C (n = 7) formed double layer smectic A (S_A) phases. The hydrogen bonding among the carboxylic acid groups and the segregation between the carboxylic acid groups and the alky chains played important roles in forming the mesophases. In addition, the solution self‐assembly behaviors were also preliminarily investigated through the fluorescent probe technique and transmission electron microscopy, and vesicles with uniform sizes were observed. The weak hydrophilicity and large degree of freedom of the carboxylic acid group and the relative rigidity of the polymer chain due to the “jacketing” effect were responsible for the formation of the structures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Higher aliphatic polyaldehydes. II. Polymer structure and polymer stability of poly(n-heptaldehyde)

Poly(n-heptaldehyde) has been prepared by anionic and cationic polymerization at ?60°C in methyl cyclohexane. The anionic polymer is more crystalline and of a higher degree of isotactic structure than the somewhat rubbery but still crystalline cationic polymer. The polymers have been acetate-endcapped to improve their thermal stability. Cationic polymer, when endcapped and purified, begins to degrade above room temperature; even crystalline anionic polymer degrades at a reasonable rate at 100°C. The crystallinity of poly(n-heptaldehyde) is caused by crystallization of the acetalic main chain as well as the side chain. Two regions of melting have been recognized by DSC analysis and by microscopic observations. The low melting region between 80 and 100°C has been identified as the melting of the paraffinic side chains of poly(n-heptaldehyde). It consists of three clearly definable endotherms at 78, 87, and 101°C.     

Anionic graft polymerization of ethylene oxide on starch. II. Structure of the graft polymers

Starch–poly(ethylene oxide) graft polymers were prepared in DMSO at various monomer and starch alkoxide concentrations. Complimentary and varied information on the structure of the graft polymers was obtained from NMR and periodic acid oxidation of the polymers. From the NMR spectra of the graft polymers in pyridine containing a trace of HCl, which causes shifting of the resonance of the internal ? CH₂O? protons from the terminal ? CH₂OH protons, the polyethylene oxide content, the DP _n of the grafted side chains, and the efficiency of the alkoxides were calculated. With increase of the alkoxide concentration there was a small decrease in ? DP _n, and in the efficiency of the alkoxides in initiating graft polymerization. With increase of monomer concentration, there was only a small increase in ? DP _n but a large increase in the efficiency, indicating the existence of transfer reactions between the growing anions and the free hydroxyl groups on the starch. The results of he periodic acid oxidation showed that with increase of alkoxide concentration there was no significant change in the per cent oxidation of the graft polymers, but with increase of monomer, there was an increase in the participation of the secondary hydroxyl groups in initiation. This supports the NMR evidence for the existence of transfer reactions leading to ? DP _n values much lower than those calculated from [monomer]/[catalyst] ratios.     

Synthesis of comb‐type polycarbosilanes via nucleophilic substitution reactions on the main‐chain silicon atoms

A series of comb‐type polycarbosilanes of the type [Si(CH₃)(OR)CH₂]_n {where R = (CH₂)_mR′, R′ = ? O‐p‐biphenyl? X [X = H (m = 3, 6, 8, or 11) or CN (m = 11)], and R′ = (CF₂)₇CF₃ (m = 4)} were prepared from poly(chloromethylsilylenemethylene) by reactions with the respective hydroxy‐terminated side chains in the presence of triethylamine. The product side‐chain polymers were typically greater than 90% substituted and, for R′ = ? O‐p‐biphenyl? X derivatives, they exhibited phase transitions between 27 and 150 °C involving both crystalline and liquid‐crystalline phases. The introduction of the polar p‐CN substituent to the biphenyl mesogen resulted in a substantial increase in both the isotropization temperature and the liquid‐crystalline phase range with respect to the corresponding unsubstituted biphenyl derivative. For R = (CH₂)₁₁? O‐biphenyl side chains, an analogous side‐chain liquid‐crystalline (SCLC) polysiloxane derivative of the type [Si(CH₃)(O(CH₂)₁₁? O‐biphenyl)O]_n was prepared by means of a catalytic dehydrogenation reaction. In contrast to the polycarbosilane bearing the same side chain, this polymer did not exhibit any liquid‐crystalline phases but melted directly from a crystalline phase to an isotropic liquid at 94 °C. Similar behavior was observed for the polycarbosilane with a fluorocarbon chain, for which a single transition from a crystalline phase to an isotropic liquid was observed at ?0.7 °C. The molecular structures of these polymers were characterized by means of gel permeation chromatography and high‐resolution NMR studies, and the crystalline and liquid‐crystalline phases of the SCLC polymers were identified by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 984–997, 2003     

Semiconducting polymers based on charge-transfer complexes. II. Crystal structure of poly-N-4-[4-(methylthio)phenoxy]butyrylethylenimine

Of the two electron-donor-containing polymers whose synthesis was described in Part I of this series, one was crystalline. This polymer, which contains (methylthio)phenoxy electron-donating groups on the side chains of an N-acyl-substituted polyethylenimine, could be indexed in a triclinic unit cell of dimensions a = 4.35 Å, b = 24.0 Å, c = 12.7 Å, and α = β = γ = 90°. The polymer has the side chains alternating on each side of the polymer backbone. They extend to form at 24.0 Å repeat in that direction. The thickness of the ribbonlike molecule is 4.35 Å, while the repeat distance along the polymer backbone is 12.7 Å, which includes four monomer units.     

Order in poly(N-(10-n-alkyloxycarbonyl-n-decyl)-maleimides)

Wide-angle and small-angle x-ray diffraction patterns of 11 poly(N-(10-n-alkyloxycarbonyl-n-decyl)maleimides) (PEMI) (including only even members of the series) have been obtained on unoriented samples. They show major maxima at two diffraction angles. The one at the larger angles is due to the interaction of neighboring n-alkyl side-chains. The smaller one (which shows second and third orders of diffraction in higher members of the series, n = 14 to n = 22, where n is the number of methylene groups in the external n-alkyl sequence in the side chain) is related to the distance between lamellar planes formed by the main chains. In all cases, the measured layer separation d_i is higher than the structural unit length L of the side-chain in the most extended conformation, and lower than the length corresponding to two side-chains. On the basis of the experimental results reported here, a model is proposed for the packing of these comblike polymers in the solid state. The mode of packing is also supported by infrared spectra in the 720 cm^?1 region for the ? CH₂? rocking mode of vibration of the n-alkyl side-chain.     

Synthesis and characterization of polyimides from imidazole-blocked 2,5-bis[(n-alkyloxy)methyl]-1,4-benzene diisocyanates and pyromellitic dianhydride

From imidazole-blocked 2,5-bis[(n-alkyloxy)methyl]-1,4-benzene diisocyanates and pyromellitic dianhydride a series of new rigid-rod polyimides (C_n-PY-PI; n = 4, 6, 8) having linear and flexible (alkyloxy)methyl ((SINGLE BOND)CH₂OC_nH_{2n + 1}; n = 4, 6, 8) side chains were prepared and characterized and their properties were measured and discussed with regard to effects of side chains. Incorporation of the side chains onto the rigid main chain greatly enhanced the solubility and fusibility of the polymers, and melting point of C₈-PY-PI was determined to be 277°C. The UV-VIS absorption behavior was independent of side-chain length. TGA thermograms revealed a two-step pyrolysis behavior, in which the side chains split off separately at lower temperatures. X-ray diffractograms showed that all the polyimides are crystalline at room temperature. Sharp reflections in small-angle region obviously indicated the presence of a layered crystal structure. © 1996 John Wiley & Sons, Inc.