Mesomorphic properties of cholesteric side‐chain liquid crystalline polysiloxanes and elastomers

A series of crosslinked liquid crystalline polymers and corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization. Their liquid crystalline properties were characterized by differential scanning calorimetry, polarizing optical microscopy, and X‐ray diffraction measurements. The results showed that the crosslinking obtained in the isotropic state and the introduction of nonmesogenic crosslinking units into a polymeric structure could cause additional reduction of the clearing point (T_i) of the crosslinked polymers, compared with the corresponding uncrosslinked polymers. The crosslinked polymers (P‐2–P‐4) with a low crosslinking density exhibited cholesteric phases as did the uncrosslinked polymers. In contrast, a high crosslinking density made the crosslinked polymer P‐5 lose its thermotropic liquid crystalline property. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 773–778, 2004     

Preparation and properties of Mahua oil‐based liquid crystalline pentalkyds

Medium oil length Mahua oil‐based pentalkyds are prepared with varying degree of excess hydroxyl. These alkyds are subsequently converted into liquid crystalline form by copolymerizing with p‐hydroxy benzoic acid (p‐HBA). Esterification is facilitated by dicyclohexyl carbodiimide (DCC). Graft efficiencies of copolymers are calculated and reported. Characterization of grafted alkyds is carried out using IR, DSC, and polarizing microscope techniques. A sharp melting point indicates liquid crystalline characteristic of p‐HBA grafted alkyds. DSC and polarizing microscope study results further substantiated the observation. Mechanical film properties of LC resins viz., hardness, impact resistance, and adhesion are also reported and compared with the amorphous counterparts. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Viscosity‐reducing effects of two semiflexible liquid‐crystalline polyesters with different chain rigidities in a matrix of polycarbonate

Two liquid‐crystalline polyesters (LCPs) with different chain rigidities were synthesized and melt‐blended with polycarbonate (PC) at an LCP concentration of 2 wt %. The first LCP (LCP1) was based on hydroxybenzoic acid (HBA), hydroquinone (HQ), sebacic acid (SEA), and suberic acid (SUA) and contained a relatively high concentration of flexible units (SEA and SUA). The other one (LCP2) was based on HBA, hydroxynaphthoic acid, HQ, and SEA and contained a lower concentration of flexible units. LCP2 had a much lower melting point, a higher clearing temperature, and a lower shear viscosity than LCP1. The blending was carried out at 265, 280, and 300°C for both systems. The extent of the viscosity reduction induced by the addition of LCP1 depended on the compounding temperature, and the lowest viscosity was achieved with blending at 280°C. This was attributed to the large interfacial area and interactions between the flexible segments of LCP1 and PC chains at the interface. For PC/LCP2, the viscosity reduction was not significantly dependent on the compounding temperature, and when it was compounded at 280°C, its viscosity was significantly higher than that of PC/LCP1 at high shear rates, even though LCP2 had lower viscosity. A scanning electron microscopy study revealed that, with compounding at 265 and 280°C, LCP2 was poorly dispersed in the PC matrix in comparison with LCP1, and the glass‐transition‐temperature depression caused by the addition of LCP2 was relatively small. This indicated that interfacial interactions in PC/LCP2 were weaker, thereby explaining their different rheological behavior in comparison with PC/LCP1. With compounding at 300°C, the compatibility of both systems improved because of transesterification reactions, but this did not lead to a lower viscosity because of the lack of physical interfacial interactions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 960–969, 2004     

Curing behavior of liquid crystalline epoxy/DGEBA blend

The effect of liquid crystalline epoxy (LCE) resin on the curing behavior and thermomechanical properties of diglycidylether of bisphenol A (DGEBA) was investigated. LCE was blended with DGEBA and curing behavior of the blend was studied according to LCE content in the blend. Curing of DGEBA was accelerated and thermomechanical properties of DGEBA were considerably improved by the addition of LCE, which acted as a molecular reinforcement. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Toughening liquid‐crystalline polymers with polyethylenes containing epoxy functionality

To improve toughness, a liquid‐crystalline polymer (LCPs) was blended with polyethylenes containing epoxy functionality in concentrations of 2, 6, and 15 wt %. The blends were prepared with a corotating twin‐screw extruder and were injection‐molded into specimens for mechanical testing. The effect of the amount of the epoxy‐functionalized polyethylenes on the morphology and mechanical and thermal properties was studied. The toughness improved with increasing amount of functionalized polyethylene, and the blend containing 15 wt % epoxy‐functionalized polyethylene had the best toughness properties. Impact strength values up to three times higher than those of the neat LCP were achieved. However, the stiffness of the LCP concurrently decreased substantially. The morphology became much more uniform, and the melting behavior changed. The results show that considerable improvements in the toughness properties of LCPs can be achieved with epoxy‐functionalized polyethylenes. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1886–1891, 2002     

Synthesis and curing of liquid crystalline epoxy resin based on asymmetric mesogen

A novel liquid crystalline epoxy resin (LCER) derived from asymmetric mesogen unit was synthesized. Its structure and liquid crystalline behavior were characterized by hydrogen nuclear magnetic resonance (H‐NMR), differential scanning calorimetry (DSC), polarized optical microscopy (POM). The results indicated that the LCER converted to a nematic phase at 85°C during heating and finally became isotropic at 145°C. The curing behavior and phase behavior of the LCER with 4,4′‐diaminodiphenyl methane and methyl hexahydrophthalic anhydride were also studied by DSC and POM, respectively. Their apparent activation energy (E_a) was evaluated according to the Ozawa's isoconversional method. The results suggested that autocatalytic reaction had occurred in these two systems. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Determination of the phase diagram of HBA‐HNA liquid crystalline polymer/polycarbonate blends

The phase diagram of blends of liquid crystalline polymer (LCP) and polycarbonate (PC) was constructed. The effect of temperature on morphological development in melt‐blended samples was examined with a polarized light microscope, in conjunction with a heating stage. Phase separation in the blend was observed as the temperature was increased. For a particular LCP/PC blend composition, two‐phase separation temperatures (T_sp1 and T_sp2) were determined. Consequently, the corresponding phase diagram relating to phase separation was constructed. It was divided into three regions. No phase separation occurred when the blend was below T_sp1. However, a slight phase separation was detected when the temperature was between T_sp1 and T_sp2. Moreover, pronounced phase separation was observed when the blend was at a temperature above T_sp2. The phase‐separated structure varied according to the initial composition of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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     

Preparation of liquid crystalline networks doped with azobenzene molecules and their photochemical grating formation behavior

Liquid crystalline (LC) networks with macroscopically uniaxial molecular orientation were prepared by photopolymerization of mixtures of LC mono‐ and diacrylates and a donor–acceptor azobenzene compound in a homogeneous glass cell at the nematic phase, and their photoresponsive properties were investigated. The transparency of the LC networks decreased with a decrease in the crosslinking density with LC diacrylate. The LC networks crosslinked with a few mol percent of LC diacrylate showed an enantiotropic phase transition from an anisotropic phase to an isotropic phase as well as high transparency. Formation and removal of the grating were investigated by irradiating two writing beams with an argon ion laser. Grating less than 1.0 μm could be achieved, and the response time of formation and removal of the grating were in a range of a few tens of microseconds. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 943–951, 2003     

Synthesis and thermotropic liquid‐crystalline behavior of novel main‐chain poly(aryl ether ketones)

Novel aromatic poly(ether ketones) containing bulky lateral groups were synthesized via nucleophilic substitution reactions of 4,4′‐biphenol and (4‐chloro‐3‐trifluoromethyl)phenylhydroquinone (CF‐PH) with 1,4‐bis(p‐fluorobenzoyl)benzene. The copolymers were characterized by differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, and polarized light microscopy observation. Thermotropic liquid‐crystalline behavior was observed in the copolymers containing 40, 50, 60, and 70 mol % CF‐PH. The crystalline–liquid‐crystalline transition [melting temperature (T_m)] and the liquid‐crystalline–isotropic phase transition appeared in the DSC thermograms, whereas the biphenol‐based homopolymer had only a melting transition. The novel poly(aryl ether ketones) had glass‐transition temperatures that ranged from 143 to 151°C and lower T_m's that ranged from 279 to 291°C, due to the copolymerization. The polymers showed high thermal stability, and some exhibited a large range in mesophase stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1347–1350, 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     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

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     

Effect of interfacial interaction on rheological behavior of blends of a semiflexible liquid‐crystalline polyester and polycarbonate

A liquid‐crystalline polyester based on hydroxybenzoic acid, hydroquinone, sebacic acid, and suberic acid (named as BQSESU) was melt blended with polycarbonate (PC) at the BQSESU concentration of 2 wt %. It was found that the extent of viscosity reduction induced by the addition of BQSESU depends on the compounding temperature and the relation between them is not monotonic. The lowest viscosity was achieved by blending at 280°C. GPC measurements indicate that molecular weight reduction induced by the compounding is not a major contributor to the viscosity reduction. SEM study shows that when compounded at 280°C the blend is partially miscible with particle size at the submicron level. At the same time a large T_g depression was observed, which indicates strong interactions between the flexible segments of BQSESU and PC in the interfacial regions. The lowest viscosity achieved by blending at 280°C is thus proposed as an interfacial phenomenon. When compounded at 265°C, BQSESU particle size is larger, which gives a small interfacial area and hence less viscosity reduction. When compounded at 300°C a nearly miscible morphology was achieved, which also leads to less viscosity reduction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3051–3058, 2003     

Preparation of polymer‐dispersed liquid crystal films containing a small amount of liquid crystalline polymer and their properties

Polymer‐dispersed liquid crystal (PDLC) films were synthesized by the copolymerization of liquid crystalline polymer (LCP) precursor, urethane acrylate (UA), and mesogenic monomer (AI) at different conditions. The morphology of polymer matrix changed with the weight ratio of polymer/liquid crystal (LC) ratio and curing temperature, resulting in a large change in the droplet size of LC domains in the PDLC film. The components used in the synthesis of polymer matrix, that is, the weight ratio of LCP, AI, and UA, also strongly influenced the morphology of PDLC films. A small amount of LCP was copolymerized with UA and AI in the preparation of polymer matrix to improve the electrooptical properties such as the viewing angle. Added LCP also affected the morphology and the properties of PDLC. The hydrophobicity of LCP caused changes in the droplet size of LC domain in PDLC films and the anchoring energy between matrix polymer and LC droplets. As the hydrophobicity of the matrix increases, the droplet size of LC domain also increases; on the contrary, anchoring energy decreased, leading to the decrease of driving voltage. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3178–3188, 2000     

Synthesis and liquid‐crystalline properties of poly(4‐vinylpyridinium) bromides N‐substituted with dialkyloxyterphenyl groups

Poly(4‐vinylpyridine)s (P4VPs) fully and partially quaternized with dialkyloxyterphenyl groups were synthesized and characterized. These new polymers developed both liquid‐crystalline (LC) properties and a light emission (luminescence) in the blue region. The mesomorphic behavior of the polymers was initially characterized by differential scanning calorimetry and polarizing optical microscopy and was further corroborated by X‐ray diffraction analyses. The X‐ray diffraction patterns showed in the low‐angles region several equidistant diffraction peaks (d₀₀₁, d₀₀₂, d₀₀₃, …) and in the wide‐angles region a broad peak typical of nonordered mesophases. From d₀₀₁ and the length of the monomers, we deduced that the molecular arrangement in the mesophase corresponded to a double‐layered stacking of molecules with mesogens tilted with respect to the smectic plane and the backbones sandwiched between. In this arrangement, the different parts of mesogens are segregated from one another in layered domains. The longer smectic periods observed for copolymers indicated that the nonsubstituted pyridine cycles were sandwiched between two smectic layers. The emission spectra of these polymers were characterized by a broad signal centered at 365 nm. The combination of LC properties with luminescence in the polymers is interesting for the preparation of thin films with aligned emitters, particularly for linearly polarized light emission. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

New arylidene–siloxane polyethers: Liquid‐crystalline and photosensitive properties

By polycondensation reactions, starting from α, ω‐bis(chloromethyl)polydimethylsiloxanes with different molecular weights and 2,6‐bis(4‐hydroxybenzylidene)cyclohexanone, new polyethers were obtained. The structure of resulting polymers was confirmed by IR and ¹H‐NMR spectroscopy and their thermal properties and mesophase behavior were studied by TGA, DSC, and polarizing light microscopy. Depending on the length of the siloxane spacer, some of the obtained compounds exhibited thermotropic liquid‐crystalline properties. A possible smectic texture was investigated by X‐ray diffraction measurements at room temperature. A decrease of the transition temperatures values was observed as the spacer length increased. The photochemical behavior of the siloxane polyethers was studied by ultraviolet absorption spectroscopy. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3093–3099, 2003     

Experimental results for the rheological and rheo‐optical behavior of poly(ethylene terephthalate)/liquid‐crystalline polymer blends

The use of thermoplastic/liquid‐crystalline polymer (LCP) blends is recognized as a good strategy for reducing viscosity and improving mechanical properties relative to pure thermoplastics. This improvement, however, is only noticeable if the LCP fibrillates, in situ, during processing and the fibrils are kept in the solid state. In this article, we report a morphological, rheological, and rheo‐optics study performed with two blends of poly(ethylene terephthalate) with a LCP, Rodrun LC3000 (10 and 25 wt % LCP content), and we show that the obtained droplet‐shape relaxation time (the time the deformed droplet took to regain its spherical form after the cessation of flow) allowed for the explanation of the morphological observations. In fact, the droplet‐shape relaxation time was higher for the blend with higher LCP content, for the higher experimentally accessible shear rates, and still increased at the highest shear rate, which explained the fibrils of the LCP dispersed phase observed in this blend, whereas for the lower LCP content blend, the droplet‐shape relaxation time reached a low‐value plateau for higher shear rates, which explained the absence of fibrillation in this blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

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 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