Synthesis of chiral helical poly[p-(oligopinanylsiloxanyl)phenylacetylene]s and enantioselective permeability of their membranes

To develop better polymeric materials for optical-resolution membranes, we synthesized nine chiral phenylacetylenes containing pinanyl groups. We used them to investigate the effects of chemical structures, including the number and position of the chiral groups in the monomers, on the induction of chirality in the main chain during polymerization and on the degree of enantioselectivity in the permeation of the polymeric membranes. The monomers included six new chiral p-(oligomethylpinanylsiloxanyl)phenylacetylenes. The homopolymerizations of these nine monomers with a Rh complex produced high-molecular-weight polymers (molecular weight = 10⁵–10⁶). Of the five polymers with a chiral pinanyl group at the 1-position of each oligosiloxanyl group, all except for two polymers showed high molar ellipticity in the main-chain region in the circular dichroism spectra. This finding indicated that these polymers had a chiral helical main chain. The membranes fabricated from all the polymers synthesized in this study were high-quality, except for two polymers. All these membranes showed enantioselective permeabilities for two amino acids and an alcohol. The membranes from the polymers with a chiral helical backbone, a high content of pinanyl groups, no oligodimethylsiloxane moieties, or a combination of these showed good enantioselectivities (= 1.7–640) in permeation. We propose that the sense of the main-chain helicity determined the selectivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4502–4517, 2004     

Main‐chain,thermotropic, liquid‐crystalline,hydrogen‐bonded polymers of 4,4′‐bipyridyl with aliphatic dicarboxylic acids

A series of main‐chain, thermotropic, liquid‐crystalline (LC), hydrogen‐bonded polymers or self‐assembled structures based on 4,4′‐bipyridyl as a hydrogen‐bond acceptor and aliphatic dicarboxylic acids, such as adipic and sebacic acids, as hydrogen‐bond donors were prepared by a slow evaporation technique from a pyridine solution and were characterized for their thermotropic, LC properties with a number of experimental techniques. The homopolymer of 4,4′‐bipyridyl with adipic acid exhibited high‐order and low‐order smectic phases, and that with sebacic acid exhibited only a high‐order smectic phase. Like the homopolymer with adipic acid, the two copolymers of 4,4′‐bipyridyl with adipic and sebacic acids (75/25 and 25/75) also exhibited two types of smectic phases. In contrast, the copolymer of 4,4′‐bipyridyl with adipic and sebacic acids (50/50), like the homopolymer with sebacic acid, exhibited only one high‐order smectic phase. Each of them, including the copolymers, had a broad temperature range of LC phases (36–51 °C). The effect of copolymerization for these hydrogen‐bonded polymers on the thermotropic properties was examined. Generally, copolymerization increased the temperature range of LC phases for these polymers, as expected, with a larger decrease in the crystal‐to‐LC transition than in the LC‐to‐isotropic transition. Additionally, it neither suppressed the formation of smectic phases nor promoted the formation of a nematic phase in these hydrogen‐bonded polymers, as usually observed in many thermotropic LC polymers. The thermal transitions for all of them, measured by differential scanning calorimetry, were well below their decomposition temperatures, as measured by thermogravimetric analysis, which were in the temperature range of 193–210 °C. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1282–1295, 2003     

The synthesis and properties of side‐chain liquid‐crystal polymers with a chiral center

The synthesis and mesomorphic properties of six monomers and six side‐chain liquid‐crystal polymers with a chiral center are described. The polysiloxanes were prepared by the hydrosilation of monomers with poly(hydromethylsiloxane)s. Most of the polymers exhibit a wide range of the chiral smectic C phase (SmC*). © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1609–1617, 2000     

Liquid crystalline copolymers containing electron donor and acceptor mesogens with a chiral group in the spacer unit

Side-chain liquid crystalline polymers containing both mesogenic (carbazolylmethylene)aniline and (4′-nitrobenzylidene)aniline units with various spacer groups were prepared to examine effects of the structure of spacer groups on the liquid crystalline properties. The copolymer containing (R)-(+)-2-methylpropylene as a chiral group in the spacer unit induced a smectic phase; the copolymer with a trimethylene spacer of similar length to the chiral spacer exhibited a nematic phase. Smectic phases were observed for the copolymer containing the chiral spacer group when the proportion of the carbazolyl group was in the range of 0.55–0.88. For example, the copolymer with the proportion of the carbazolyl group of 0.68 expressed the smectic phase from 88° to 167°C. This isotropic temperature was 37° higher than the calculated value (130°C) based on an assumed copolymer composition without the electron donor–acceptor interaction. Thus, it is assumed that for the chiral copolymer containing both electron donor and acceptor groups, the thermal stability and the induction of the smectic phase were caused by both the electron donor–acceptor interaction and the existence of the chiral group in the spacer unit. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of azobenzene‐containing poly(1‐alkyne)s with different functional pendant groups

1‐Alkynes containing azobenzene mesogenic moieties [HC?C(CH₂)₉? O? ph? N?N? ph? O? R; R = ethyl ( 1 ), octyl ( 2 ), decyl ( 3 ), (S)‐2‐methylbutyl ( 4 ), or (S)‐1‐ethoxy‐1‐oxopropan‐2‐yl ( 5 ); ph = 1,4‐phenyl] were synthesized and polymerized in the presence of a Rh catalyst {(nbd)Rh⁺[B(C₆H5)₄]^?; nbd = 2,5‐norbornadiene} to yield a series of liquid‐crystalline polymers in high yields (e.g., >75%). These polymers had moderate molecular weights (number‐average molecular weight ≥ 12,000), high cis contents in the main chain (up to 83%), good thermal stability, and good solubility in common organic solvents, such as tetrahydrofuran, chloroform, and dichloromethane. These polymers were thoroughly characterized by a combination of infrared, nuclear magnetic resonance, thermogravimetric analysis, differential scanning calorimetry, polarized optical microscopy, and two‐dimensional wide‐angle X‐ray diffraction techniques. The liquid‐crystalline behavior of these polymers was dependent on the tail group attached to the azobenzene structure. Poly‐ 1 , which had the shortest tail group, that is, an ethyl group, showed a smectic A mesophase, whereas poly‐ 2 , poly‐ 3 , and poly‐ 5 , which had longer or chiral tail groups, formed smectic C mesophases, and poly‐ 4 , which had another chiral group attached to the azobenzene structure, showed a chiral smectic C mesophase in both the heating and cooling processes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4532–4545, 2006     

Synthesis and characterization of novel liquid‐crystalline copolymers containing thermally stable photochromic groups

To overcome the defects of the thermal instability of azobenzene, a series of novel photochromic, chiral, liquid‐crystalline monomers and polymers were synthesized from (+)‐camphor. The copolymerization of the photochromic monomers with comonomers was carried out. The synthesized monomers and polymers were identified with nuclear magnetic resonance, Fourier transform infrared, and elemental analysis. The composition of the copolymers was estimated with elemental analysis. The specific rotation of the chiral compounds and polymers was evaluated. The thermal stability and phases of the polymers during heating and cooling cycles were studied with differential scanning calorimetry and thermogravimetric analysis. The phases of the polymers were identified with polarized optical microscopy textures and X‐ray diffraction analysis. The distance between the layers of smectic liquid crystals was estimated from the diffraction angles. Photoisomerization of the configurational E/Z structures was investigated with an ultraviolet–visible spectrophotometer with 300‐nm ultraviolet irradiation. The thermal stability of the Z‐structural segment in the polymers was confirmed through the heating of the polymer at 70 °C for over 10 h. The photoisomerization and thermal stability of the C?C bond in the polymeric materials were demonstrated through a series of novel chiral polymers synthesized in this investigation. Both the polarity of the center part and the molecular length at the ends of the molecules were found to be necessary factors for the formation of liquid‐crystalline molecules. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2026–2037, 2007     

Helical pitch of ferroelectric liquid-crystalline polymers and copolymers

Ferroelectric liquid-crystalline polymers and copolymers were synthesized from acrylate polymers with side chains consisting of a flexible spacer unit, a mesogenic unit and an optically active substituent. In the chiral smectic C (S*_c) phases typical fan-shaped textures with equidistant lines (caused by the helical structures) were observed. It was found that the helical pitch increased with increasing polymer molecular weight. The helical pitch also increased in copolymers containing mixtures of right- and left-handed chiral side chains.     

A novel type of optically active helical polymers: Synthesis and characterization of poly(N‐propargylureas)

This article presents two novel artificial helical polymers, substituted polyacetylenes with urea groups in side chains. Poly( 4 ) and poly( 5 ) can be obtained in high yields (≥97%) and with moderate molecular weights (11,000–14,000). Poly( 4 ) contains chiral centers in side chains, and poly( 5 ) is an achiral polymer. Both of the two polymers adopted helical structures under certain conditions. More interestingly, poly( 4 ) exhibited large specific optical rotations, resulting from the predominant one‐handed screw sense. The helical conformation in poly( 5 ) was stable against heat, while poly( 4 ) underwent conformational transition from helix to random coil upon increasing temperature from 0 to 55 °C. Solvents had considerable influence on the stability of the helical conformation in poly( 4 ). The screw sense adopted by the helices was also largely affected by the nature of the solvent. Poly( 4 ‐co‐ 5 )s formed helical conformation and showed large optical rotations, following the Sergeants and Soldiers rule. By comparing the present two polymers (with one ? N? H groups) with the three polymers previously reported (with two ? N? H groups in side chains), the nature of the hydrogen bonds formed between the neighboring urea groups played big roles in the formation of stable helical conformation. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4112–4121, 2008     

Untwisting of the helical superstructure in the cholesteric and chiral smectic C*phases of cross-linked liquid-crystalline polymers by strain

It is possible to untwist reversibly the helical superstructure of elastomers with cholesteric and chiral smectic C*phases by using strain. In that way a cholesteric structure can be transformed into a nematic structure and a chiral smectic C*into a smectic C structure. The latter case is especially interesting because a structure without a macroscopic polarization (chiral smectic C*) is transformed into one with a macroscopic polarization (smectic C like arrangement).     

Untwisting of the helical superstructure in the cholesteric and chiral smectic C∗phases of cross-linked liquid-crystalline polymers by strain

Abstract

It is possible to untwist reversibly the helical superstructure of elastomers with cholesteric and chiral smectic C?phases by using strain. In that way a cholesteric structure can be transformed into a nematic structure and a chiral smectic C?into a smectic C structure. The latter case is especially interesting because a structure without a macroscopic polarization (chiral smectic C?) is transformed into one with a macroscopic polarization (smectic C like arrangement).     

Polymeric liquid crystals: structural basis for ferroelectric and nonlinear optical properties

This paper describes the rational design and structure–property relations in three different types of polar LC polymers with interesting material properties, as follows. (i) Chiral LC polymers, which are functionalized with crosslinkable groups, can be converted into LC elastomers with chiral smectic C^* phases. The mechanical orientability of these elastomers leads to new piezoelectric materials. (ii) The curing (dense crosslinking) of a polymer matrix provides one possibility of stabilizing the polar order of dye molecules, which is necessary for frequency doubling. Additionally, LC phases can help to stabilize this polar structure, which leads to large and stable nonlinear optical coefficients. (iii) Polymer analogous esterifications offer a convenient method for the synthesis of chiral smectic C^* polymers with large ferrolectric polarizations.     

Chiral polymers for resolution of enantiomers

In 1979, the formation of one‐handed helical poly(triphenylmethyl methacrylate) (PTrMA) was found through the helix‐sense‐selective polymerization of methacrylate using chiral anionic initiators, and the existence of a stable helical polymer without chiral side chains was proved. The chiral polymer exhibited unexpected high chiral recognition of various racemic compounds when used as the chiral packing material (CPM) for HPLC, which was commercialized in 1982 as the first chiral column based on an optically active polymer. This success encouraged us to develop further useful commercial chiral packing materials (CPMs) based on polysaccharides, cellulose, and amylose. By using these polysaccharide‐based CPMs, particularly phenylcarbamate derivatives, nearly 90% of chiral compounds can be resolved not only analytically but also preparatively, and several chiral drugs have been produced using the CPMs. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1731–1739, 2009     

Functionalized liquid-crystalline polymers towards NLO-applications and piezo-sensors

A systematic synthesis of functionalized 1c polymers is possible starting from precursor polymers with phenolic groups. The esterification of these precursor polymers with chiral acids proceeds nearly quantitatively and produces polymers with cholesteric and chiral smectic C* phases. A further functionalization of these polymers with “NLO-chromophores” produces polymers, which are suitable for second harmonic generation; a functionalization with crosslinkable groups leads to polymers, which act as piezoelements.     

Chiral soluble polymers and microspheres for enantioselective crystallization

A series of chiral polymers based on poly(N‐acryl) amino acids was synthesized using a convergent synthetic approach. These chiral polymers have been used as chiral additives to induce enantioselective crystallization of racemic or conglomerate amino acids in solutions. These polymeric additives showed strong capabilities to enhance highly enantioselective resolution during the crystallization of amino acids. In addition, these polymers caused unusual modifications of amino acid crystal morphologies. Furthermore, spherical microparticles of those same chiral polymers were also shown active in similar chiral discriminations during amino acid crystallizations occurring on microparticle surfaces. Our study demonstrates the high potential of chiral polymers and microparticles to resolve amino acids throughout crystallization processes. High enantiomeric excesses in one targeted enantiomer of amino acids can also be maximized via time‐dependent kinetic control of crystallizations. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3009–3017, 2006     

Synthesis and characterization of optically active helical vinyl polymers via free radical polymerization

A facile synthetic route to prepare the dual‐functional molecule, 2,5‐bis(4′‐carboxyphenyl)styrene, was developed. The esterification of this compound with chiral alcohols, that is, (S)‐(+)‐sec‐butanol/(R)‐(?)‐sec‐butanol, (S)‐(+)‐sec‐octanol/(R)‐(?)‐sec‐octanol, and D ‐(+)‐menthol/L ‐(?)‐menthol, respectively, yielded three enantiomeric pairs of novel vinyl monomers, which underwent radical polymerization to obtain helical polymers with an excess screw sense. These polymers exhibited optical rotations as large as fourfold those of the corresponding monomers. Their helical conformations were quite stable as revealed by the almost unchanged chiroptical properties measured at different temperatures. The polymers with linear alkyl tails in the side‐groups formed irreversibly columnar nematic phases in melt although the corresponding monomers were not liquid crystalline. Whereas, the polymers with cyclic tails generated no mesophase. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2408–2421, 2009     

Twisted smectic A phases in side chain liquid crystal polymers

The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors.     

Lyotropic liquid‐crystalline behavior of polyisocyanodipeptides

Rigid, helical polyisocyanodipeptides derived from alanine (PIAAs) that form lyotropic liquid‐crystalline (LC) phases in tetrachloroethane are presented. An investigation by optical microscopy between crossed polarizers demonstrated that PIAAs prepared by the polymerization of isocyanodipeptide monomers with an activated tetrakis isocyanide nickel(II) catalyst could form cholesteric LC phases in tetrachloroethane in concentrations between 18 and 30 wt %. Cholesteric LC phases that were formed in solutions of greater than 25 wt % displayed a reversal of the cholesteric helix upon annealing at 50 °C. Diastereomeric PIAA mixtures displayed cholesteric LC behavior only when the PIAAs had the same helix screw sense. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 981–988, 2007     

New liquid-crystalline polymers with chiral phases

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.     

Twisted smectic A phases in side chain liquid crystal polymers

Abstract

The syntheses of two side chain liquid crystal polymers, a polyacrylate and a polymethacrylate, are reported. In each of the polymers the liquid-crystalline side group carries an asymmetric carbon atom, thereby making some of the liquid crystal phases formed by the polymers optically active and chiral. For the chiral polyacrylate smectic A and chiral ferroelectric smectic C phases are observed, however for the chiral polymethacrylate a cholesteric phase is detected above the smectic A phase. It is found that the smectic A to cholesteric phase transition is mediated by the formation of an intermediary twisted smectic A phase. This intermediary phase is a liquid-crystalline analogue of the Abrikosov flux phase found in Type II superconductors.     

Thermotropic liquid‐crystalline polymers containing five‐membered heterocyclic groups. X. Relationships between structures of semirigid polyesters based on three disubstituted 2,5‐diphenyl‐1,3,4‐thiadiazoles and thermotropic liquid‐crystalline and optical properties

Thermotropic liquid‐crystalline (LC) semirigid polyesters based on three terphenyl analogues of 1,3,4‐thiadiazole (2,5‐diphenyl‐1,3,4‐thiadiazole)s (DPTD) linking undecamethyleneoxy chain at different substituted positions were synthesized from three disubstituted (4,4′‐, 3,4′‐, and 3,3′‐) dioxydiundecanols of DPTD and four diesters, and the relationships between polymer structures and LC and optical properties were investigated. DSC measurements, texture observations, and wide‐angle X‐ray analyses revealed that the polymers composed of DPTD moiety having a more linear molecular structure and 1,4‐phenylene unit or short aliphatic chain tend to exhibit LC smectic C and/or A phases. The following observations were made: (1) the emergence of smectic C and/or A phases in all the polymers on the basis of 4,4′‐disubstituted DPTD, (2) formation of enantiotropic smectic C and/or A phases in the polymers containing a 1,4‐phenylene unit in the main chain, (3) formation of a more stable smectic C phase in the polymers having a short aliphatic [(CH₂)₄] chain, and (4) a decrease of the mesomorphic property of the polyesters in the order of 4,4′‐DPTD > 3,4′‐DPTD > 3,3′‐DPTD. Solution and solid‐state ultraviolet–visible and photoluminescent spectra indicated that all the polyesters display maximum absorbances and blue emissions arising from the DPTD moiety, whose peak maxima were shifted to lower wavelengths in the order of 4,4′‐DPTD > 3,4′‐DPTD > 3,3′‐DPTD as well as the aforementioned LC property. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2676–2687, 2003