Synthesis and structure of polysiloxane liquid crystalline elastomers with a mesogenic crosslinking agent

A new mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of a nonmesogenic crosslinking agent for liquid crystalline elastomers. The synthesis of new side‐chain liquid crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 is described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and elastomers were confirmed by ¹H NMR and FTIR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking units on the phase behavior is discussed. The elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and nematic‐threaded texture. However, when the crosslinking density reached 21.6 mol %, the mesophase of polymer P‐8 disappears. The adoption of a mesogenic crosslinking agent diminishes the perturbation of a nonmesogenic crosslinking agent on mesophase of liquid crystalline elastomers, and isotropic temperature and a mesomorphic temperature range slightly decreased with increasing content of the crosslinking agent. In addition, X‐ray analysis shows nematic polydomain network polymers can transform into smectic monodomain by stress induction, leading to the orientation formation macroscopically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1736–1742, 2004     

Synthesis and Characterization of a Novel Low‐Viscosity Unsaturated Hyperbranched Polyester Resin

Hyperbranched thermosetting resin is the best additive for toughening and reinforcing linear thermosetting resin. A novel low‐viscosity unsaturated hyperbranched polyester resin (UHPR) is synthesized by the reaction between maleic anhydride monoisooctyl alcohol ester and a hydroxyl‐ended hyperbranched polyester resin (HPR) prepared from phthalic anhydride (PA) and trimethylolpropane (TMP). The structure of HPR is characterized by FT‐IR and ¹H NMR, and its degree of branching is deduced by comparing with the ¹H NMR spectrum of a model compound. The molecular weights of HPR and UHPR are determined by theoretical calculation and MALDI‐TOF MS measurements. This low‐viscosity (< 10 000 cP) novel UHPR can be applied in the field of environment‐friendly coatings and in toughening and reinforcing linear unsaturated polymers.     

Synthesis and phase behavior of nematic liquid‐crystalline elastomers derived from smectic crosslinking agent

A mesogenic crosslinking agent M‐1 was synthesized to minimize the perturbations of nonmesogenic crosslinking agent for liquid‐crystalline elastomers. The synthesis of side‐chain liquid‐crystalline elastomers containing a rigid mesogenic crosslinking agent M‐1 and a nematic monomer M‐2 was described by a one‐step hydrosilylation reaction. The chemical structures of the obtained monomers and network polymers were confirmed by Fourier transform infrared and ¹H‐NMR spectroscopy. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The influence of the crosslinking units on the phase behavior was discussed. The liquid‐crystalline elastomers containing less than 15 mol % of the crosslinking units showed elasticity, reversible phase transition, and threaded texture. The experimental results demonstrated that isotropic temperature and liquid‐crystalline range of polymers P‐1–P‐7 decreased a little as the concentration of crosslinking agent M‐1 increased, and the use of mesomorphic crosslinking agent M‐1 promotes the arrangement of liquid‐crystalline units from P‐1 to P‐5. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1712–1719, 2005     

Synthesis and phase behavior of chiral side‐chain liquid‐crystalline polysiloxanes containing two mesogenic groups

The synthesis of chiral side‐chain liquid‐crystalline polysiloxanes containing both cholesteryl undecylenate (M_I) and 4‐allyloxy‐benzoyl‐4‐(S‐2‐ethylhexanoyl) p‐benzenediol bisate (M_II) mesogenic side groups was examined. The chemical structures of the obtained monomers and polymers were confirmed with Fourier transform infrared spectroscopy or ¹H‐NMR techniques. The mesomorphic properties and phase behavior of the synthesized monomers and polymers were investigated with polarizing optical microscopy, differential scanning calorimetry, and thermogravimetric analysis (TGA). Copolymers IIP–IVP revealed a smectic‐A phase, and VP and VIP revealed a smectic‐A phase and a cholesteric phase. The experimental results demonstrated that the glass‐transition temperature, the clearing‐point temperature, and the mesomorphic temperature range of IIP–VIP increased with an increase in the concentration of mesogenic M_I units. TGA showed that the temperatures at which 5% mass losses occurred were greater than 300°C for all the polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2670–2676, 2002     

In‐situ self reinforced polyimide for film materials

A novel polyimide (PI) with mesogenic units was synthesized by the reaction between the pendent hydroxyl group of PI and the epoxy group of a liquid crystalline (LC) compound in the presence of N,N‐dimethylaniline at 120–130 °C. As a result, a novel in‐situ self‐reinforced PI film materials was obtained. The macromolecular reaction between the hydroxyl group and epoxy group was investigated by a model reaction. The properties of PI were studied by WAXD, DSC and polarized optical microscopy, and the results indicate that the polyimides with mesogenic units exhibit a smectic phase, the mesogenic units level influencing the side‐chain crystallinity, and also the thermal and mechanical properties of the polymers; the enhanced PI films possess good solubility, higher thermal stability, higher tensile strength and modulus. © 2001 Society of Chemical Industry     

Synthesis and characterization of α‐methylstilbene‐ and azobenzene‐based thermotropic liquid crystalline polymers

A series of combined liquid crystalline poly(bis‐4,4′‐oxy‐α‐methylstilbene‐4‐substituted (X) phenylazo‐4′‐phenyloxydecylphosphate ester)s bearing photoreactive mesogenic units were synthesized. FTIR and ¹H NMR spectroscopy confirmed the structures of these polymers. The inherent viscosities of the polymers were found to be in the range 0.45–0.65 dL g^?1. Polarizing optical microscopy (POM) exhibited birefringent liquid crystalline melt properties. The thermal properties of all of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The photochemical properties of these polymers were studied by UV‐visible and fluorescence spectroscopy. The influence of the photoinduced E–Z (trans–cis) isomerization of the various terminal substituents of the side‐chain azobenzenes was investigated. The kinetics of the photoisomerization process reveal the switching times for the conversion between the trans‐ and cis‐ forms of the azobenzene units. The photo‐optical properties of these polymers exhibited layered smectic phases and showed good photoinduced properties in their mesomorphic states. Copyright © 2005 Society of Chemical Industry     

Side‐chain copolymers containing smectic monomer and chiral reagent—Synthesis and characterization

A series of new chiral side‐chain liquid‐crystalline polymers were prepared containing smectic‐nematic monomer and nonmesogenic chiral monomer. All polymers were synthesized by graft polymerization using polymethylhydrosiloxane as backbone. The mesomorphic properties were investigated by differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analyses, and X‐ray diffraction measurements. The chemical structures of the monomers and polymers obtained were confirmed by Fourier transform infrared, proton nuclear magnetic resonance spectra (¹H NMR). M₁ showed smectic (S_B, S_C) and nematic phase on the heating and the cooling cycle. Polymers P₀–P₂ were in chiral smectic A phase, while P₃–P₅ were in cholesteric phase, P₆ has bad LC properties, and P₇ has no LC properties. Experimental results demonstrated that nonmesogenic chiral moiety and LC mesogenic with long carbochain offered the possibility of application because of its lower glass transition temperature, and the glass transition temperatures and isotropization temperatures and the ranges of the mesophase temperature reduced with increasing the contents of chiral agent. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Main‐chain liquid‐crystalline ionomers bearing potassium sulfonate groups

A series of thermotropic main‐chain liquid‐crystalline (LC) ionomers were prepared, which contained potassium sulfonate groups pendent to the chains. The polymers were prepared in an esterifying reaction with potassium ion contents ranging between 0 and 3.9 wt %. The content of potassium ion was characterized by spectrophotometric analysis with sodium tetraphenylboron as the titrant. Chemical structures were determined by various experimental techniques including Fourier transform IR spectroscopy and ¹H‐NMR. LC properties were characterized by differential scanning calorimetry, polarizing optical microscopy, and X‐rays. All of the polymers displayed nematic or smectic mesophases. With increasing potassium sulfonate ionic concentration in the polymers, the melting temperatures and isotropic transition temperatures changed little, whereas the temperature of the smectic A–nematic phase transition increased. The ionic aggregation was tangled with the rigid mesogenic groups of LC segments to form multiple block domains, leading the soft main chains to fold and form a lamellar structure due to their electrostatic interactions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2021–2026, 2005     

Synthesis and characterization of side‐chain liquid‐crystalline ionomers containing quaternary ammonium salt groups

A series of thermotropic side‐chain liquid‐crystalline ionomers (LCIs) containing 4‐(4‐alkoxybenzyloxy)‐4′‐allyloxybiphenyl (M) as mesogenic units and allyl triethylammonium bromide (ATAB) as nonmesogenic units were synthesized by graft copolymerization upon polymethylhydrosiloxane. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC was used to measure the thermal properties of these polymers. The mesogenic properties were characterized by polarizing optical microscopy, DSC, and X‐ray diffraction. Homopolymers without ionic groups exhibit smectic and nematic mesophases. The nematic mesophases of the ionomers disappear and the mesomorphic temperature ranges decrease with increasing concentration of ionic units. The influence of the alkoxy chain length on clearing temperature (T_c) values of ionomers clearly shows an odd‐even effect, similar to that of other side‐chain liquid‐crystalline polymers. The mesomorphic temperature ranges increase with increasing alkoxy chain length when the number of alkoxy carbon is over 3. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2879–2886, 2003     

Synthesis and mesomorphic properties of side‐chain cholesteric liquid‐crystalline polymers containing menthyl groups

A series of new cholesteric liquid‐crystalline polysiloxanes ( P₁ – P₅ ) derived from menthyl groups were synthesized. The chemical structures of the monomers and polymers were characterized with Fourier transform infrared, ¹H‐NMR, ¹³C‐NMR, and elemental analyses. The mesomorphic properties and thermal behavior were investigated with differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis, and X‐ray diffraction measurements. The influence of the polymer structure on the thermal behavior was discussed. The monomer diosgeninyl 4‐allyloxybenzoate exhibited a typical cholesteric oily‐streak texture and a focal‐conic texture. Polymers P₁ – P₅ showed thermotropic liquid‐crystalline properties. P₁ displayed a smectic fan‐shaped texture, P₂ – P₅ showed a cholesteric Grandjean texture, and P₆ and P₇ did not show mesomorphic properties. The experimental results demonstrated that the glass‐transition temperature and the clearing temperature decreased, and the mesomorphic properties weakened with an increasing concentration of menthyl units. Moreover, P₁ – P₅ exhibited wide mesophase temperature ranges and high thermal stability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:5559–5565, 2006     

Effect of Lateral Nitro Groups on the Properties of Sulfur-Ligated Twin Mesogens

The syntheses and the properties of new sulfurligated liquid crystalline sulfones, containing biphenyl units, as well as the influence of lateral nitro groups on their phase behaviour are described. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for most of the synthesized bis(4-alkoxy-biphenyl-3-yl)sulfones ( 4 ). The mesomorphic behaviour of these compounds is compared with that of the corresponding nitro compounds 6 . The bis(4-alkoxy-6-nitrobiphenyl-3-yl)sulfones ( 6 ) are not mesogenic. The results demonstrate that lateral nitro groups introduced into the biphenyl unit, changing the length-breadth relation, depress the thermal stability and lead to the loss of the mesomorphic properties.     

Synthesis of a side chain liquid crystalline polycarbonate with a chiral backbone

We report the experimental demonstration of a novel and environmentally benign supercritical carbon dioxide (ScCO₂) technique that yields an optically active, side chain liquid crystalline polycarbonate in a single‐step reaction. The obtained polymer is worthwhile, since it is highly stereoregular and can find applications in an enlarged mesomorphic temperature range compared to its acrylic analogues. The synthesized materials were characterized by IR, ¹H‐NMR, and ¹³C‐NMR, while the thermal properties were measured by DSC. Polarized optical micrograph and wide angle X‐ray diffraction were used for the mesogenic property characterization of the copolymer. The transfer chirality from the backbone to the mesophase is demonstrated on the optical microscopy textures. Being consistent with the ¹³C‐NMR, X‐ray implies an ordered polymeric structure. The DSC analysis of the copolymer indicates that the T_i (the clearing point temperature) value does not change dramatically, whereas a pronounced decrease in T_g (the glass transition temperature) value is observed from that of its acrylic analogues. Hence, the obtained polymer exhibits another practical benefit by widening the mesomorphic temperature range. This study is the insightful combination of material processing and chemical design that elucidates the advantages of ScCO₂ application, in terms of liquid crystallinity and the tacticity of the obtained polymer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1915–1921, 2006     

Synthesis of hyperbranched polyester‐amides and their application as crosslinkers for polyurethane curing systems

A series of hyperbranched polyester‐amides (S1, S2, S3) with trimethylolpropane as a core molecule were synthesized using core‐dilution/slow monomer addition strategy. The products were characterized by FTIR, ¹³C NMR, GPC, TGA, hydroxyl value measurement, and viscosity measurement. The result showed that the hyperbranched polyester‐amides synthesized had narrow molecular weight distribution and high degree of branching (DB). The hyperbranched polyester‐amides synthesized were used as crosslinkers for polyurethane curing systems and the mechanical properties of the polyurethane curing systems were investigated. It was found that the best tensile property and tear strength were obtained when the S2 were used as crosslinkers and the molar ratio of  OH and  NCO was 1 : 1. It was also found that the polyurethane curing systems had the highest hardness and T_g when the S3 were used as crosslinkers. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Synthesis and characterization of fluorine‐containing liquid crystalline polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens

Several novel side‐chain liquid crystalline (LC) polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric LC monomer cholesteryl 3‐(4‐allyloxy‐phenyl)‐acryloate and a fluoro‐containing LC monomer 4‐[2‐(3‐trifluoromethyl‐phenoxy)‐acetoxy]‐phenyl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques, such as FTIR, ¹H‐NMR, ¹³C‐NMR, TGA, DSC, POM, and XRD. The temperatures at which 5% weight loss occurred were greater than 300°C for all the polymers, and the residue weight near 600°C increased slightly with increase of the trifluoromethyl‐substituted mesogens in the fluorinated polymer systems. The samples containing mainly cholesteryl cinnamate mesogens showed chiral nematic phase when they were heated and cooled, but the samples containing more trifluoromethyl‐substituted mesogens exhibited chiral smectic A mesophase. The glass transition temperature of the series of polymers increased slightly with increase of trifluoromethyl‐substituted mesogens in the polymer systems, but mesophase–isotropic phase transition temperature did not change greatly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of trifluoromethyl‐substituted mesogens in the fluorinated polymers systems, indicating that the smectic order derived from trifluoromethyl‐substituted mesogens should be strengthened. These results should be due to the fluorophobic effect between trifluoromethyl‐substituted mesogens and the polymer matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of liquid‐ crystalline triblock copolymers by ATRP,having electron‐transporting thiadiazole unit

ABA‐type block copolymers composed of 2,5‐diphenyl‐1,3,4‐thiadiazole (DPTD) oligoester and poly(methyl methacrylate) (PMMA) segments (M_n = 16 200 and 23 000) were synthesized by atom‐transfer radical polymerization and their liquid‐crystalline (LC) and photoluminescence (PL) properties were examined. The structures of block copolymers were identified by Fourier transform infrared and ¹H NMR spectroscopies. Differential scanning calorimetry measurement, polarizing microscopy observation and wide‐angle X‐ray analysis revealed that the block copolymers form thermotropic LC phase (smectic C) independent of molecular weights of PMMA segments, but a model polymer (PMMA segments having the DPTD unit in the central part) has no LC melt. Solution and solid‐state PL spectra indicated that all the block copolymers display blue emission arising from the DPTD unit. Their quantum yields are 17–21%, which increase with the PMMA chain lengths. The block copolymers have good aligned structures in the LC states, but their order parameter (S) values in sheared LC states were lower than those in the sheared LC compounds. The PL properties in the LC states were independent of the LC aligned structures. Cyclic voltammetry measurements showed that these block copolymers have deep HOMO levels compared with polymers composed of oxadiazole rings. Copyright © 2007 Society of Chemical Industry     

Synthesis and characterization of side‐chain cholesteric liquid‐crystalline polysiloxanes containing different space groups

A series of liquid‐crystalline (LC) polysiloxanes were synthesized by two different cholesteric monomers, cholest‐5‐en‐3‐ol(3β)‐10‐undecenoate and cholesteryloxycarbonylmethyl 4‐allyloxybenzoate. The chemical structures and LC properties of the monomers and polymers were characterized by various experimental techniques, including Fourier transform infrared spectroscopy, ¹H‐NMR, elemental analysis, differential scanning calorimetry, and polarized optical microscopy. The specific rotation absolute values increased with increasing rigid spacers between the main chain and the mesogens. All of the polymers exhibited thermotropic LC properties and revealed cholesteric phases with very wide mesophase temperature ranges. With a reduction in the soft‐space groups in the series of polymers, the glass‐transition temperature and the isotropic temperature increased slightly on heating cycles. Reflection spectra of the cholesteric mesophase of the series of polymers showed that the reflected wavelength shifted to short wavelengths with decreasing soft‐space groups in the polymers systems, which suggested that the helical pitch became shorter with increasing rigid‐space groups. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Blends of liquid crystalline polyester–polyurethane and epoxy: Preparation and properties

A novel liquid crystalline polyester–polyurethane (LCPU) that contains polyester mesogenic units was synthesized in the present work. Through a careful investigation of the structure and morphology of the LCPU, it was found that the home‐synthesized LCPU is a highly birefringent thermotropic nematic liquid crystal. After being blended with bisphenol‐A epoxy, the liquid crystalline polymer can, simultaneously, improve the impact strength and the glass transition temperature as well as the tensile strength and the tensile modulus of the blends. It was proved to be an efficient toughening agent for epoxy without the expense of other properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 783–787, 2003     

Synthesis and characterization of the environmental‐sensitive hyperbranched polymers as novel carriers for controlled drug release

Novel hyperbranched polymers, which contain a hydrophobic branched poly(p‐(chloromethy)styrene) (PCMS) core and poly(N,N‐dimethylaminoethyl methacrylate) (PDMA) shell that exhibited environmental sensitivity, have been synthesized by atom transfer radical polymerization (ATRP). At first, a hyperbranched polymer (PCMS) core is obtained via ATRP of p‐(chloromethy)styrene (CMS), which may act as an “inimer”‐monomer and initiator. Then the modified hyperbranched polymers having different average arm length consisting of PCMS and PDMA are synthesized by ATRP using anterior PCMS as macroinitiators. Their macromolecular structures are characterized by FTIR and ¹H NMR. Using chlorambucil as a model drug, the behaviors of the controlled drug release from the environmental‐sensitive hyperbranched polymers with different average chain length of PDMA and degree of branching are studied. The data demonstrate that the rate of the drug release can be effectively controlled by pH value, and these environmental‐sensitive hyperbranched polymers have the potential to be used as novel carriers in some controlled drug release systems in the future. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 311–316, 2006     

Synthesis and self-assembly of hyperbranched polyester peripherally modified by touluene-4-sulfonyl groups

In this paper, hyperbranched polyesters (HPs) were synthesized in the molten state from 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) and 2-ethyl-2-hydroxymethyl-1,3-propanediol (TMP) using acid catalysis. The modified hyperbranched polyesters were obtained through the chemical modification of the hyperbranched polyester cores by substituting a controlled fraction of the terminal hydroxyl groups with touluene-4-sulfonyl chloride using triethylamine (TEA) as an acceptor of HCl. The resultant polyesters were characterized by ¹H NMR, ¹³C NMR, FT-IR, UV and GPC and their self-assembly behaviors were investigated. The results revealed that self-assembled structures could be formed in selected solvents (trichloromethane/acetone or trichloromethane/n-hexane).     

Mesomomorphism enhancement of modified side‐chain liquid‐crystalline polysiloxanes by copolymerization

The liquid‐crystalline (LC) monomer 4‐allyoxybenzoyloxy‐4′‐buthylbenzoyloxy‐p‐phenyl (M₁), whose LC phase appeared at lower temperatures, from 137 to 227°C, and the modified mesogenic monomer 4‐allyoxybenzoyloxy‐4′‐methyloxybenzoyloxy‐p‐biphenyl (M₂), whose LC phase appeared at higher temperatures, from 185 to 312°C, were prepared. A series of side‐chain LC polysiloxanes containing M₁ and M₂ were prepared by graft copolymerization. Their LC properties were characterized by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction. The results show that the introduction of the modified mesogenic monomer M₂ into the polymeric structure caused an additional increase in the clearing point (isotropic transition temperature) of the corresponding polysiloxanes, compared with unmodified polysiloxanes, but did not significantly affect the glass‐transition temperature. Moreover, the modified polysiloxanes exhibited nematic phases as the unmodified polymer did. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1196–1201, 2005