Synthesis and characterization of network liquid crystal elastomers and thermosets

A new series of network liquid crystal polymers were synthesized by graft copolymerization of the difunctional mesogenic monomer 4‐allyloxy‐benzoyloxy‐4′‐allyloxybiphenyl (M) upon polymethylhydrosiloxane (PMHS). Monomer M acted not only as a mesogenic unit but also as a crosslinker for the network polymers. The chemical structures of the polymers were confirmed by IR spectroscopy. DSC, TGA, and X‐ray scattering were used to measure their thermal properties and mesogenic properties. The glass transition temperature (T_g) of these network liquid crystal polymers was increased when the monomer was increased, and T_d (temperature of 5% weight loss) at first went up and reached a maximum at P₁, then went down. The slightly crosslinked polymers (P₀, P₁) show rubber‐like elasticity, so it was called liquid‐crystal elastomer. Network polymers will lose elasticity property with a highly crosslinked degree, and turn into thermosetting polymers (P₄, P₅). All polymers exhibited a smectic texture by X‐ray scattering. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1104–1109, 2002     

Influence of rare earth compounds on the anionic ring-opening polymerization of cyclosiloxanes

The influence of rare earth compounds on the polymerization of cyclosiloxanes has been studied for hexamethylcyclotrisiloxane (D₃) and octamethylcyclotetrasiloxane (D₄). In both cases, it has been shown that rare earth compounds alone do not lead to well defined polymers: yields are never quantitative and the formation of cyclic side-products is always observed. The influence of these compounds has also been studied in the anionic polymerization of the same cyclosiloxanes initiated by organolithium reagents or fluorides. In the case of D₃, it has been shown that back-biting reactions can be slowed down in the presence of rare earth compounds whereas for D₄, both polymerization and back-biting reactions get slower. Received: 22 May 1997/Revised: 8 September 1997/Accepted: 8 September 1997     

Properties of some polysilane polymers: (n-PrSiMe)n, (i-PrSiMe)n, and (sec-BuSiMe)n

Three polysilane polymers, (n-PrSiMe) _n , (i-PrSiMe) _n , and (sec-BuSiMe) _n , were synthesized and characterized by DSC. UV spectroscopy, wide-angle X-ray diffraction, and optical microscopy, all at variable temperatures. The known thermochromic transition of (n-PrSiMe) _n at 48 C is associated with a change from an orthorhombic to an isotropic phase. (i-PrSiMe) _n was examned as an insoluble and soluble (lowM _w) fraction, both existing mainly in an orthohombic lattice at room temperature. (sec-BuSiMe) _n has a mesophase structure at 25 C, undergoes a weak endothermic transition to a second (nematic) mesophase near 65 C, and becomes isotropic at 160 C.Dedicated to the memory of Professor Zygmunt Lasocki, a fine chemist and a kind and gentle person.     

Behaviour of the miscibility of poly(ethylene oxide)/liquid crystal blends

The microscopic behaviour of blends of poly(ethylene oxide) with two different low molecular weight liquid crystals (LC) was studied in order to evaluate miscibility. One of the liquid crystal components had a phase transition temperature lower than the melting temperature of poly(ethylene oxide) (PEO), and the other a higher value. The low molecular weight liquid crystal components were 4-cyano-4′-n-heptylbiphenyl (7CB) and p-cyanophenyl p-pentyloxybenzoate (pCP). Thermal analysis and polarized optical and scanning electron microscopy were employed. The melting temperature (T_m) depression of PEO increased with LC content in the blend, suggesting that the PEO was miscible with both liquid crystals in the isotropic phase. The spherulitic structural morphology of the semicrystalline components is affected by the presence of liquid crystals. © 1998 SCI.     

Synthesis and phase behavior of cholesteric liquid crystal polymers containing glutamic acid in main‐chain

Four polymers (P₀–P₃) containing peptide chain as polymer backbone were synthesized by condensation reaction with bis(trichloromethyl)carbonate and triethylamine. The chemical structures of the monomers M₀–M₃ were confirmed by FTIR and ¹H‐NMR. The structure–property relationships of the monomers and polymers are discussed. Their phase behavior and optical properties were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. Monomers M₁–M₃ and polymers P₁–P₃ displayed cholesteric phases. The results demonstrated that the melt temperature and clear point of monomers (M₁–M₃) and polymers (P₁–P₃) decreased with the increase of the flexible spacer length in the side‐chain, and the mesophase temperature range of the polymers increased with the increase of the flexible spacer length. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Anionic polymerization of cyclosiloxanes in heterogeneous medium

Anionic polymerization of various cyclosiloxanes [octamethylcyclotetrasiloxane (D₄), 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane (V₄), and hexamethylcyclotrisiloxane (D₃)] was performed. As catalysts, IRA-900 and PB-100 type anionites with benzyltrimethylam-monium and 3-acrylamidopropylbenzyldimethylammonium groups, respectively, were used. The anionite with higher strongly basic exchange capacity (IRA-900) is more efficient in dimethylcyclosiloxane polymerization. PB-100 anionite with less strongly basic capacity is more active for polymerization of the V₄ monomer with bulky and electronegative sub-stituent. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of side-chain liquid crystalline polysiloxanes

The synthesis and characterization are described for a series of side-chain liquid crystal polysiloxanes using polyhydrosilylation reaction between a poly(hydrogen methyl-co-dimethylsiloxanes),-(OSiHMe)_x,-(OSiMe2)_y-, where x/y was 13/87, 30/70, 55/45, 73/27 and 98/2, and [4-(allyloxy)benzoyll biphenyl mesogenic group. The side-chain liquid crystal polysiloxanes were characterized by¹H NMR,¹³C NMR, IR, gel permeation chromatography (GPC), differential scanning calorimetry (DSC) and optical polarizing microscopy. The dimethylsiloxane segment factors governing thermal transition temperatures and activation energy (E_a) of the nematic-to-isotropic phase transition are discussed.     

Synthesis and properties of liquid crystalline polyurethane elastomers

Novel type of mesogenic chain extenders used in this study are N,N′‐bis(4‐hydroxyphenyl)‐3,4,3′,4′‐biphenyldicarboxyimide (BPDI) and N,N′‐bis[4‐(6‐hydroxyhexyloxy) phenyl]‐3,4,3′,4′‐biphenyldicarboxyimide (BHDI). BHDI has a flexible spacer of 6‐methylene units but BPDI does not. The liquid crystalline polyurethane elastomers were synthesized from BPDI or BHDI as a mesogenic chain extender, 4,4′‐diphenylmethane diisocyanate, and poly(oxytetramethylene)glycol (MW 1000) as a soft segment. Polyurethane based on BHDI exhibited two melting transitions. However, any melting behavior was not shown in the BPDI‐based polyurethanes because of higher melting temperature than decomposition temperature. The composition of polyurethanes was varied as a means of manipulating liquid crystalline behavior and physical properties. The BHDI‐based polyurethanes containing above 50 wt % of hard segment content exhibited nematic liquid crystal behaviors. As the hard segment content of the BHDI‐based polyurethanes increased, the glass transition temperature (T_g), strength, modulus, and the amount of hydrogen bonding increased. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 577–585, 2000     

Anionic polymerization and copolymerization of cyclosiloxanes initiated by trimethylsilylmethyllithium

Summary A novel initiator, i.e. trimethylsilylmethyllithium has been successfully used for the ring opening polymerization of cyclosiloxanes, in toluene or in the bulk, in the presence of the cryptand [211] or DMSO. Suitable conditions have been found in which monomodal distributions of molecular weights are observed for homopolymers of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane (V₄) as well as for copolymers of V₄ with D₃ or D₄. Laboratoire de Chimie Macromoléculaire associé au CNRS, URA 24     

Morphology and thermal properties of liquid crystal p‐PAEB/n‐propyl methacrylate copolymers

The copolymers of p‐phenylene di{4‐[2‐(allyloxy) ethoxy]benzoate} (p‐PAEB) with n‐propyl methacrylate (PMA) were synthesized. The liquid crystalline behavior and thermal properties of copolymers were studied by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), X‐ray diffractometer (XRD), and torsional braid analysis (TBA). The results of XRD, POM, and DSC demonstrate that the phase texture of copolymers is affected by the composition of liquid crystal units in copolymers. The POM and XRD reveal that liquid crystal monomer (p‐PAEB) and copolymers of p‐PAEB with PMA are all smectic phase texture. The dynamic mechanical properties of copolymers are investigated with TBA. The results indicate that the phase transition temperatures and dynamic mechanical loss peak temperature T_p of copolymers are affected by the composition of copolymers and liquid crystal cross networks. The maximal mechanical loss T_p is 114°C and is decreased with added PMA. The behaviors of phase transition are affected by the crosslinking density, and it is revisable for lightly crosslinking LC polymer networks, but it is nonreversible for the densely crosslinking of LC polymer networks. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Investigations of Construction and in vitro Release of Curcumin Lyotropic Liquid Crystals: Phase Diagrams,Small Angle X-ray Scattering,Rheological Technology,and Release Kinetics

In this study, hexagonal and cubic lyotropic liquid crystals (LLC) were constructed in Brij 97-Tween 40 (MS₈₂, MS₆₄ and MS₄₆)/OLA/H₂O systems to encapsulate curcumin. MS₈₂, MS₆₄, and MS₄₆ indicated that the mass ratio of Brij 97/Tween 40 was 8/2, 6/4, and 4/6. The microstructure of curcumin LLC was studied using small angle X-ray scattering (SAXS). Phase diagrams showed that the increase of MS reduced the phase transition temperature (T_C). Particularly, the T_C of sample C₁Cur [Brij 97-Tween 40 (MS₄₆)/OLA/H₂O = 50.0/2.8/47.2] and C₂Cur [Brij 97-Tween 40 (MS₄₆)/OLA/H₂O = 50.0/25.0/25.0] was 37.6 and 35.4 °C, respectively, close to the temperature of the human body. Thus, the shear rheology and SAXS were used to study the structural changes of samples C₁Cur and C₂Cur with temperature. The moduli values of samples C₁Cur and C₂Cur decreased with the increase of temperature, showing various structural strengths. in vitro release experiment was used to study the drug release kinetics. The release of curcumin from LLC conformed to the concentration diffusion model. Due to a similar a_S, the release of curcumin from samples A₁Cur, B₁Cur, and C₁Cur (Brij 97-Tween 40/OLA/H₂O = 50.0/2.8/47.2 and the MS is MS₈₂, MS₆₄, and MS₄₆) showed a similar release behavior under different MS. The release behavior of curcumin was related to the structure of samples C₁Cur and C₂Cur at different temperatures. Curcumin exhibited the fastest release rate when the samples behaved as the micellar phase.     

Phase and Rheological Properties of a Curcumin-Encapsulated Cubic Liquid Crystal

For the purpose of encapsulating curcumin, cubic liquid crystals were constructed using a Brij 97‐NaDC (surfactant)/IPM‐PEG 400 (oil)/H₂O system, at a constant Brij 97/NaDC ratio of 4:1 and varied IPM/PEG 400 ratios of 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, and 3:7. The cubic liquid crystal samples, possessing a fixed surfactant/oil/water composition and different IPM/PEG 400 ratios, underwent a structure transition from Im3m to the coexistence of Im3m and Ia3d as determined by small‐angle X‐ray scattering (SAXS) measurements. SAXS and rheological investigations on the 5:5 IPM/PEG 400 ratio cubic samples suggested that the cubic liquid crystals became more stable after encapsulating curcumin in either IPM or PEG 400, as indicated by the longer characteristic relaxation time. By saturating curcumin in both IPM and PEG 400, at an IPM/PEG 400 ratio less than 5:5, higher elastic modulus, larger q value, and stronger intensity of the first scattering peak for the curcumin‐encapsulated liquid crystals were observed as compared to the corresponding curcumin‐free samples. Also, clearly different melting points for these systems were found. These results indicate a method of tailoring the stability and the temperature sensitivity of the investigated curcumin‐encapsulated cubic liquid crystals.     

Atom-Transfer Radical Polymerization to Synthesize Novel Liquid Crystalline Diblock Copolymers with Polystyrene and Mesogen-jacketed Liquid Crystal Polymer Segments

The synthesis of a series of new rod-coil diblock copolymers with different molecular weights and low polydispersity was achieved by atom transfer radical polymerization. The block architecture (coil-conformation of styrene segment and rigid-rod conformation of 2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene segment) of the diblock copolymers was experimentally confirmed by proton nuclear magnetic resonance (¹H NMR) and differential scanning calorimetry (DSC). The liquid crystalline behavior of the copolymers was studied using DSC and a polarized optical microscope (POM). It was found that the liquid crystalline behavior was dependent on the molecular-weight of the rigid segment. Only those copolymers with M _n of the rigid block beyond 9,300 g/mol could form liquid crystalline phases above the glass transition temperature of the rigid block.     

Alignment layer relaxation—a technique for assessing thermal transitions in polymer films

We introduce a method for assessing the glass transition temperature (T_g) of thin polymer films. The technique may be applied to any polymer film that can effect liquid crystal alignment, and is demonstrated here for a commercial polyamide-imide. The method leverages the ability of the polymer film to align nematic liquid crystals on its surface, when that surface has been prepared by mechanical brushing. Relaxation of the alignment layer, brought about by thermal cycling through T_g, is seen to affect liquid crystal alignment, and thus serve as a T_g indicator. The technique reveals a three-order-of-magnitude change in the measured property. The method allows the assessment of that portion of the film responsible for aligning liquid crystals, and provides an indication of the efficacy of alignment. Our results imply that the relaxation of the surface in Probimide 32 occurs over a range of temperatures, and relaxation is not complete until the film is heated to a temperature above the glass transition of the bulk polymer.     

Effect of polymer structures on electro-optical properties of polymer stabilized liquid crystal films

The polymer stabilized liquid crystal (PSLC) film is a relatively novel electro-optical material, which is generally obtained by dissolving a small amount of a bifunctional photoreactive monomer in a low molecular mass liquid crystal. In this paper, the PSLC films were prepared with photoreactive biphenyl methacrylate monomers by photopolymerization induced phase separation. The effects of liquid crystal concentration, curing time, monomer structures and alignment layer on the electro-optical properties of PSLC films were investigated. The results show that the transmittance in the OFF state (T _OFF) increased with the liquid crystal concentration, but the driving voltage decreased. T _OFF was also influenced by the curing time. Furthermore, when polyimide was used as alignment layer, the films prepared from the bifunctional monomer shows a higher T _OFF, while those from the single functional monomer exhibited a deformed electro-optical curve due to the unsteady polymer networks. __________ Translated from Polymer Materials Science and Engineering, 2008, 24(1): 63–66 [译自: 高分子材料科学与工程]     

Recoverable shear strain of liquid crystal‐forming concentrated hydroxypropyl cellulose solutions

The recoverable shear strain (S_R) for the liquid crystal‐forming hydroxypropyl cellulose solutions was determined by means of a concentric cylinder rotational apparatus as functions of shear stress prior to recovery and concentration of the solutions at 30°C. S_R greatly depended on shear stress and concentration; the phase of the solution (the single phase or biphase) governed the dependences of S_R on stress and concentration. S_R increased with increasing stress for the single phase and decreased for the biphase. S_R seemed to be related to the die swell (B): S_R ∝ Bⁿ. S_R exhibited a maximum and a minimum with respect to concentration. S_R for the cellulosic cholesteric liquid crystalline solutions was greater than that for the isotropic solutions. A model was proposed for explaining the greater S_R. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 865–872, 2002     

Phase behavior and structural properties for the triton X-100/<Emphasis Type="Italic">n</Emphasis>-C<Subscript>n</Subscript>H<Subscript>2n+1</Subscript>COOH/H<Subscript>2</Subscript>O system

In the Triton X-100/n-C_nH_2n+1COOH/H₂O system, n-C_nH_2n+1COOH can be used as a cosurfactant. As its chain length increases, the regions of the microemulsions showing oil-in-water (O/W), water-in-oil (W/O), and bicontinuous structures decrease and at the same time, the region of the lamellar liquid crystal increases. In the O/W region, the distribution coefficient K of n-C_nH_2n+1COOH between Triton X-100 micellar phase and water phase increases with the chain length of saturated unbranched monocarboxylic acid. The relationship between the standard solubilization Gibbs free energy of saturated unbranched monocarboxylic acid and the number of methylene groups in the saturated unbranched monocarboxylic acid is given by the equation: ΔG _m ⁰=−2.364−2.818 n(CH₂) kJ·mol⁻¹ in the Triton X-100 micellar system. In the lamellar liquid crystal region, small-angle X-ray diffraction shows that the thickness of the bilayer d ₀ is independent of the weight ratio of n-C_nH_2n+1COOH to Triton X-100, but the volume of the solvent penetrating from the solvent layer to the amphiphilic bilayer increases with the weight ratio of n-C_nH_2n+1COOH to Triton X-100. Furthermore, the d ₀ value increases with the chain length of saturated unbranched monocarboxylic acid, which will contribute to the formation and stabilization of the lamellar liquid crystal.     

Cationic polymerization initiated by intercalation compounds of Lewis acids

The results of initial studies showing the high activity of intercalation compounds of Lewis acids (C₃₀SbCl₅, C₇₇FeCl₃, C₆₄AlBr₃) as initiators of the cationic polymerization of cyclosiloxanes are presented. The influence of some reaction conditions on the yield and the molecular mass of the polymers formed is described.     

VIscometric behaviour of Kevlar fibre filled liquid crystalline solutions of ethyl cellulose in m-cresol

Liquid crystalline solutions of ethyl cellulose in m-cresol were mixed with Kevlar® fibres, and the viscometric behaviour with respect to temperature of those filled systems was determined with a cone-plate type viscometer. The viscosity of the systems exhibited a maximum and a minimum at temperatures denoted by T_max and T_min' respectively. The effects of fibre on the critical temperatures (T_max and T_min) and critical concentrations (C_a and C_b) and on the viscosity enhancement are discussed. T_max and T_min decreased with fibre concentration for single-phase anisotropic solutions, whereas they increased for the biphasic solution. The critical concentrations increased with fibre concentration and C_b was more sensitive to the fibre than C_a. The viscosity enhancement due to the fibre depended on the phase of solution. In the single-phase (isotropic and anisotropic), the viscosity enhanced with fibre; however, in the biphasic solution, the effect was not simple. The viscosity enhancement for the single-phase anisotropic solutions with fibre was lower than that for the isotropic solutions.     

Structural studies on Ca3Al4MgO10 (C3A2M)—A ternary phase in the system CaO–Al2O3–MgO

In a sequence of temperature-dependent solid-state reactions in the system CaO–Al₂O₃–MgO the formation of the ternary phase Ca₃Al₄MgO₁₀ or C₃A₂M has been studied. Whereas the compound could not be prepared at 1200°C, a yield of 85 wt.-% of Ca₃Al₄MgO₁₀ was obtained at 1320°C (incongruent melting point: 1330°C). Powder diffraction data compare well with results of previous investigations from the 1960s. Single crystals of Ca₃Al₄MgO₁₀ could be retrieved from the sinter-pellets. Basic crystallographic data are as follows: orthorhombic symmetry, space group Pbcm, a = 5.14073(8), b = 16.7576(2), c = 10.70977(16) Å, V = 922.61(2) ų, Z = 4. Using synchrotron diffraction data it was possible to solve the crystal structure. Least-squares refinements resulted in a residual of R(|F|) = 0.021 for 1000 independent observed reflections with I > 2σ(I) and 97 parameters. The structure contains [TO₄]-tetrahedra (T=Al,Mg) forming a three-dimensional (3-D) framework whose topological characteristics have been determined. Al-Mg distributions on the different T-sites have been studied. The calcium cations are located in voids of the network. More than 50 years after its first observation our investigation clarifies the crystal structure of a compound belonging to a system that is of relevance for several fields of materials science.