Jian-She Hu

Synthesis, structure and properties of new chiral liquid crystalline monomers and homopolysiloxanes containing menthyl groups

The synthesis is described of four new chiral liquid crystalline monomers (M2–M5 ) and their corresponding side‐chain homopolysiloxanes (P2–P5 ) containing menthyl groups. Chemical structures were characterised using FT‐IR or 1H NMR spectra, and specific optical rotations were evaluated with a polarimeter. The phase behaviour and mesomorphic properties of the new compounds were investigated by differential scanning calorimetry, thermogravimetric analysis, polarising optical microscopy, UV/visible/NIR spectrocopy and X‐ray diffraction. The monomers and homopolymers with more aryl segments showed noticeably lower specific optical rotation value. The monomers M2–M5 formed a cholesteric or blue phase when a flexible spacer was inserted between the rigid mesogenic core and the terminal menthyl groups by reducing the steric effect. M2–M5 revealed enantiotropic cholesteric phase. Moreover, M2 also exhibited a monotropic smectic A (SmA) phase, and M4 also exhibited a cubic blue phase on cooling. The selective reflection of light shifted to the long wavelength region with increasing rigidity of the mesogenic core for M2–M5 . P2–P5 exhibited SmA phases, and the mesogenic moieties were ordered in smectic orientation with their centres of gravity in planes. Melting or glass transition temperature and the clearing temperature increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic core.

Synthesis and phase behaviour of chiral liquid crystalline monomers based on menthyl groups, smectic polymers and cholesteric elastomers

The synthesis of new chiral liquid crystal monomers (M1 −M4 ) derived from menthyl groups, the corresponding smectic polymers (P1 −P4 ), and cholesteric elastomers (E1 −E4 ) based on M2 and crosslinking agent (CA ) is presented. The chemical structures and purity were characterised by Fourier transform infrared, 1H nuclear magnetic and elemental analyses. The phase behaviour and mesomorphism were investigated by differential scanning calorimetry, polarising optical microscopy, thermal gravimetric analysis and X-ray diffraction. The selective reflection of light for M1 −M4 was characterised with ultraviolet/visible/near infrared. The structure–property relationships of M1 −M4 and P1 −P4 were studied. The effect of the content of mesogenic crosslinking units on phase behaviour and mesomorphism of E1 −E4 was discussed. By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, M1 −M4 all showed strong mesomorphism and exhibited an oily streak and focal conic textures of the cholesteric phase, or the broken fan-shaped texture of the smectic C* phase and the platelet texture of a cubic blue phase. P1 −P4 exhibited batonnet textures of the smectic A phase, indicating that the liquid crystal polymers with siloxane chains tended to form a lower order smectic phase. For M1 −M4 or P1 −P4 , the melting temperature Tm , the isotropic temperature Ti and the glass transition temperature Tg increased, and the mesophase temperature range widened with increasing rigidity of the mesogenic units or decreasing spacer length. E1 −E4 exhibited a cholesteric texture because of the introduction of the nematic crosslinking unit. By increasing the content of the crosslinking unit, the general tendency is toward increased Tg and decreased Ti .

Synthesis and phase behaviour of new biodegradable liquid crystalline polycarbonate derived from side chain cholesteryl derivative

ABSTRACT A new cholesterol side-functionalised polycarbonate was synthesised through a coupling reaction between the terminal carboxyl group of the monomer 6-cholesteroxy-6-oxocaproic acid (COHA) and side hydroxyl group of the polycarbonate (PHTMC). The chemical structures of the intermediate compounds, monomers and polymers obtained in this study were characterised with FT-IR and 1H NMR spectrum. Their phase behaviour and thermal stability were investigated using polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis. The monomer COHA showed a cholesteric phase, while the corresponding cholesterol side-functionalised polycarbonate P(TMC-g-COHA) revealed a smectic A phase. This behaviour was attributed to an increased density of the mesogenic units in side chain and hence an ordered organisation into the mesophase. Furthermore, P(TMC-g-COHA) could exhibit a liquid crystalline state below body temperature (≈37°C). This fact indicated it could be used clinically as a self-assemble material with orientational-order mesophase. In addition, P(TMC-g-COHA) had a good thermal stability, the corresponding thermal decomposition temperature was 241°C. Graphical Abstract

New chiral liquid crystal monomers and cholesteric polyacrylates: synthesis and characterisation

The synthesis of new chiral monomers (M1 −M3 ) based on menthol and the corresponding polyacrylates (P1 −P3 ) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, 1H-NMR, elemental analyses, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The effect of the mesogenic core rigidity, spacer length and menthyl steric effect on the phase behaviour of M1 −M3 and P1 −P3 is discussed. The expected mesophase of the compounds based on menthol can be obtained by inserting a flexible spacer between the mesogenic core and the terminal groups. For the chiral monomers and polyacrylates, their corresponding melting temperature (T m), glass transition temperature (T g) and clearing temperature (T i) increased with an increase of the mesogenic core rigidity; while the T m, T g and T i decreased with increasing the spacer length. M1 and P1 showed no mesophase, while M2 and M3 all revealed a SmC* and cholesteric phases. P2 and P3 only showed a cholesteric phase.

New side chain liquid crystal aliphatic polycarbonate with pendant functionalized diosgenyl groups: I. Synthesis and mesomorphism

A new side chain liquid crystal aliphatic polycarbonate bearing side-functionalized diosgenyl mesogen, well-defined amphiphilic block copolymer mPEG43-b-P(MCC-DHO)11 was synthesized through the ring-opening polymerization and coupling reaction. The chemical structures and average molecular weights of the monomers and copolymers obtained in this study were characterized using Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H NMR) spectrum, and gel permeation chromatographic (GPC) measurement. Their mesomorphism was investigated with differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and variable-temperature x-ray diffraction (XRD) measurement. As a result, the monomer DHO and copolymer mPEG43-b-P(MCC-DHO)11 all exhibited fan-shaped texture of a smectic A (SmA) phase on heating and cooling cycles. Furthermore, mPEG43-b-P(MCC-DHO)11 revealed a LC state at body temperature. In addition, XRD suggested that mPEG43-b-P(MCC-DHO)11 showed a SmAd phase and exhibited interdigitated packing of side chains.

New chiral liquid crystalline monomers, polymers, and elastomers derived from menthol derivatives: synthesis and mesomorphism

To investigate liquid crystalline properties and structure relationships of chiral compounds based on menthol, a series of new chiral monomers derived from menthol derivatives, a mesogenic crosslinking agent, the corresponding side chain homopolymers with siloxane backbone, and cholesteric elastomers were synthesized. The structures and purity of these chiral compounds obtained in this study were characterized using FTIR, 1H NMR, and elemental analyses. The mesomorphism and thermal stabilities were investigated using differential scanning calorimetry, polarizing optical microscopy, thermogravimetric analysis, and X-ray diffraction. The selective reflection of light for the chiral monomers was studied with UV/visible/near IR. The effect of the crosslinking agent content on the phase transition temperatures of the elastomers was discussed. It was found that these chiral monomers seemed beneficial for the formation of the mesophases when a flexible spacer was inserted between the mesogenic core and the terminal menthyl groups. All obtained chiral monomers showed a cholesteric phase, chiral smectic C phase, and cubic blue phase. The crosslinking agent exhibited a smectic A (SA) phase and nematic phase. However, their corresponding homopolymers with siloxane chains tended to form a lower order SA phase. With an increase of the mesogenic rigidity, the melting temperatures, glass transition temperatures (Tg), and isotropic temperatures (Ti) of chiral monomers or homopolymers all increased. For the elastomers, general tendency was toward increased Tg and Ti with increasing the crosslinking agent content.

Study on new chiral liquid crystalline monomers and polymers containing menthyl groups

A series of new chiral monomers (M1–M4) and the corresponding siloxane polymers (P1–P4) containing menthyl groups were synthesised to establish the relationship between their structure and liquid crystalline properties. The effect of the mesogenic core rigidity and the spacer length on the phase behaviour of the monomers and polymers obtained in this study was discussed. The selective reflection of light for the chiral monomers was studied with UV-Vis spectrometer. Polarising optical microscopy, differential scanning calorimetry, X-ray diffraction and thermogravimetric analysis were used to characterise the phase behaviour and thermal stabilities. It was found that these chiral monomers and polymers were beneficial for the formation of the mesophases when a flexible spacer was inserted between the mesogenic core and terminal menthyl groups. M1–M3 showed enantiotropic chiral smectic C phase and cholesteric phase, and monotropic cubic blue phase on cooling cycle. M4 only showed cholesteric phase. P1–P4 showed a smectic A phase. With increasing the mesogenic core rigidity or decreasing the spacer length, the corresponding melting temperatures, glass transition temperatures and isotropic temperatures all increased.

Synthesis and phase behavior of chiral liquid crystalline polymeric networks derived from menthol

The synthesis of new chiral monomer 4-(menthyloxyacetoxy- benzoyloxy)biphenyl-4′-(2-(undec-10-e noyloxy)ethoxy)benzoate (ML), crosslinking agent 4-(undec-10-enoyloxy)biphenyl-4′-(2-(undec-10-enoyloxy)ethoxy)benzoate (CA), and liquid crystal polymer networks (E1−E5) containing menthyl group is presented. Their chemical structures and phase behavior were characterized with Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H-NMR), elemental analyses, polarizing optical microscopy, differential scanning calorimetry, thermogravimetric analysis (TGA), and X-ray diffraction. The selective reflection of light for ML was investigated with ultraviolet/visible/near infrared (UV/Visible/NIR). By inserting a flexible spacer between the mesogenic core and the terminal menthyl groups, ML could form mesophase and show a chiral smectic C phase, cholesteric phase and cubic blue phase. CA displayed a smectic A phase and nematic phase. The polymer networks containing less than 12 mol% of the crosslinking units showed reversible cholesteric phase transition, wide mesophase temperature range, and excellent thermal stability. With increasing the content of crosslinking unit, the corresponding Tg increased, the Ti decreased, and the mesophase temperature range narrowed for E1−E5. TGA showed that the Td(5%) was greater than 330°C for E1−E5.

Synthesis and mesomorphism of new aliphatic polycarbonates containing side cholesteryl groups

ABSTRACT New cholesterol side-functionalised polycarbonate polymers were synthesised by the ring-opening homo- and copolymerisation reaction of the cyclic monomer cholesteryl 5-methyl-2-oxo-1,3-dioxane-5-carboxylate and d,l-lactide using Sn(Oct)2 as a catalyst. The chemical structures and average molecular weights of the cyclic monomer, homopolymer and block copolymers obtained in this study were characterised using FT-IR, 1H NMR and gel permeation chromatographic measurement. The mesomorphism and mesophase structure were investigated with polarising optical microscopy, differential scanning calorimetry and X-ray diffraction measurement. As a result, the homopolymer and block copolymers showed an enantiotropic smectic A (SmA) phase. With the concentration of the lactide segment increasing, the glass transition temperature and isotropic temperature of the corresponding block copolymer all decreased. In addition, XRD suggested that the homopolymer and two block copolymers showed the SmA double-layer packing of side chains. GRAPHICAL ABSTRACT

1,2-Propanediol-linked chiral symmetric and non-symmetric liquid crystal dimers containing trifluoromethyl

ABSTRACT Four symmetric and non-symmetric chiral liquid crystal dimers containing trifluoromethyl groups, termed as TFBA-PD-TFBA, UEBBA-PD-TFBA, UEBA-PD-TFBA and UEA-PD-TFBA, respectively, have been synthesised and characterised. UEA-PD-TFBA exhibited chiral nematic phase, whereas the other three dimers displayed chiral smectic A phase. X-ray diffraction (XRD) has revealed the structure of the smectic A phase for TFBA-PD-TFBA to be intercalated, whereas that for UEBBA-PD-TFBA and UEBA-PD-TFBA to be monolayer and interdigitated, respectively. In addition, the weaker peak corresponding to a shorter layer spacing was observed for UEBBA-PD-TFBA and UEBA-PD-TFBA. Considering the results of XRD measurements and computer simulations, the structural model corresponding to the shorter layer spacing is assigned as horseshoe-like shape. The absence of smectic behaviour for UEA-PD-TFBA reveals that the weaker aromatic–aromatic interactions cannot stabilise the smectic A phase. GRAPHICAL ABSTRACT