Thermotropic main chain liquid crystalline polyesters containing ferrocene and phosphate units: synthesis and characterization

A new series of liquid crystalline main chain copolyesters were prepared, having ferrocene in the mesogenic segment and a methyl phosphate group along with a methylene spacer. The even numbered methylene groups were varied from two to ten. Liquid crystalline behaviour was investigated on a hot stage optical polarized microscope. Thermal properties of the polymers were analysed by TGA and DSC, revealing that the polymers yield high char products, probably caused by the formation of phosphorus and iron oxides. The glass transition (T _g) temperatures of the polymers were found to be fairly low, the result of the incorporation of bulky phosphorus and ferrocene moieties in the chain. The phase behaviour was analysed and correlated with the structure of the polymers. The liquid crystalline textures of the polymers became more transparent with increasing spacer length. Energy minimized structures for the polymer repeating units reveal that both the ferrocene and phosphorus moieties produce more molecular entanglement, thus reducing the T _g and T _m of the polymers.     

Liquid-crystalline side chain polymethacrylates II. Variation of spacer and central linkage in nitro-terminated polymers

The thermal behaviour and the mesogenic properties of liquid-crystalline side chain polymers with the structure are described with n = 3, 6, 8 or 11 and Z = -COO-, -CONH- or -N=N-. The polymers were made by radical chain polymerization. Most of them exhibit smectic phases, nematic phases were not observed. The amide linkage which has not yet been described as a structural element in such polymers gives rise to polymers of high polarity and high glass transition temperatures (T_g). In all cases the amide polymers produced the highest T_g values, the ester polymers showing the lowest. The azo polymers exhibited the largest mesophase ranges and the highest clearing temperatures (T_c1) of all the materials investigated. Whereas the T_c1 values for the azopolymers are nearly independent of the length of the spacer those of the amide and ester polymers show rising clearing points with increasing spacer length.     

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.     

Synthesis and characterization of halogen-containing ferroelectric liquid crystals and side chain liquid crystalline polymers

A new series of ferroelectric liquid crystals and side chain liquid crystalline polymers based on halogen-containing chiral centres has been synthesized. Chemical structures were analysed by NMR. Liquid crystal phases were characterized by differential scanning calorimetry, optical polarizing microscopy, and X-ray diffractometry. The behaviour of the liquid crystalline phases was investigated as a function of spacer units and differing terminal asymmetric moieties. It was found that phase transition temperatures decreased with increasing length of the oligooxyethylene spacer unit. Differing terminal asymmetric moieties led to differing mesophase phenomena. Furthermore, a wide temperature range (including room temperature) of a chiral smectic C phase was achieved.     

Synthesis and characterization of novel poly（aryl ether）s containing naphthyl moieties

Two poly(aryl ether)s containing naphthyl moieties were prepared from bis(3,5-dimethyl-4-hydroxyphenyl)naphthyl methane (monomer 1) via nucleophilic aromatic substitution polycondensation with bis(4-fluorophenyl) ketone and bis(4-fluorophenyl) sulfone.The structures of these polymers were confirmed by ~1H NMR.The M_n values of the two polymers were 96,200 and 88,600, respectively.The polymers exhibited good thermal stabilities with 5%mass loss at T>400℃and high glass-transition temperature(T_g) of T>250℃...     

Consequences of the 'jacketed' effect on mesomorphic and orientational properties of 'side-on fixed' liquid crystalline polymers

The mesomorphic properties have been studied as a function of the degree of polymerization for certain 'side-on fixed' polyacrylates. A peculiar evolution of the clearing temperature, T_IN, as well as of the glass transition temperatures, T_g, revealed that beyond a certain backbone length, T_IN and T_g decrease as the main chain length increases. The nematic 'jacketed' structure of these polymers induces a more or less high anisotropy of the polymer backbone conformation in the nematic phase and this can counterbalance the usual effect of an increase in the degree of polymerization on the thermodynamical properties of these systems. This evolution allows us to explain the unusual diamagnetic anisotropy anomaly observed as a function of temperature for this type of polymer.     

Investigations of polarization profiles in sandwich cells containing a liquid crystalline polymer by using the heat wave method (LIMM)

The laser intensity modulation method (LIMM) was applied to the investigation of polarization distributions in sandwich cells of a side chain liquid crystalline polymer (LCP). The thermal poling procedure using a pulsating electric field was carried out for the nematic phase at 80°C. After cooling down the samples to room temperature T_R (i.e. below the glass transition temperature, T_g) a rather perfect alignment of the side chains could be obtained. Our first LIMM investigations at T_R show a nearly homogeneous polarization profile in the LCP layer.     

Liquid crystalline and photoactive poly[4,4′-stilbeneoxy]alkylbiphenylphosphates

A series of liquid crystalline and photoactive polymers were synthesized from biphenylphosphorodichloridate with various 4,4′-bis(m-hydroxyalkyloxy)stilbenes (m = 2, 4, 6, 8, 10) in chloroform by solution polycondensation method using an acid scavenger. The resultant polymers were characterized by inherent viscosity, FT-IR, ¹H, ¹³C and ³¹P NMR spectroscopies. The liquid crystalline (LC) properties were studied using HOPM and DSC and it was inferred that out of the five polymers synthesized, higher methylene chain containing polymers (m = 6, 8, 10) exhibited LC properties. Thermogravimetric analysis revealed that all the polymers were stable in between 290 and 367 °C and underwent degradation thereafter. The thermal stability and char yield of the polymers decreased with increase in flexible methylene chain. The photochemical properties of these polymers were investigated by UV and fluorescence spectroscopy. Crosslinking proceeds via 2π-2π cycloaddition reaction of the -CHCH- of the stilbene moieties. The rate of crosslinking increases with increase in methylene chain length in the polymer backbone. The fluorescence spectra showed that the longer methylene spacer containing polymers exhibited larger red-shifts than the shorter spacer containing polymers.     

Effect of molecular structure on mesomorphism XXI. Monodisperse tetrameric model compounds for liquid crystalline polymers

Twinned dimeric mesogens having a rigid-flexible-rigid molecular structure have been shown to be appropriate models for some properties of regularly alternating (rigid-flexible)_n main chain liquid crystalline polymers (lcps). A family of tetrameric monodisperse liquid crystalline model compounds chemically related to known main chain liquid crystalline polymers of the 4-alkoxyphenyl 4'-alkoxy-benzoate type has been synthesized. The tetramers are nematogenic. Alternations in thermodynamic parameters (ΔH, ΔS) for the N-I transition as a function of spacer chain length indicate conformational behaviour of the internal spacers dominates mesophase properties.     

Synthesis and characterization of side‐chain liquid‐crystalline poly(ethyleneimine)s with cyanobiphenyl groups

A series of polyethyleneimine‐based side‐chain liquid‐crystalline polymers substituted with different ratios of cyanobiphenyl as pendent mesogenic groups has been synthesized in which the spacer length varies between two and six methylene units. The structures of the synthesized polymers are confirmed by infrared and ¹H nuclear magnetic resonance spectroscopy. The thermal properties of these polymers have been investigated using differential scanning calorimetry, polarized optical microscopy and X‐ray diffraction. The results indicate that the thermal behaviour of the polymers is strongly dependent on the degree of substitution. Polymers containing more than 69% of mesogenic groups exhibit nematic‐type thermotropic liquid‐crystalline behaviour with schlieren textures. Below this limit, the polymers are amorphous. Polymers with a higher degree of substitution present the crystalline states. The phase transition temperatures increase and the mesomorphic temperature ranges widen with increasing degree of substitution. The clearing temperatures decrease as the spacer length increases. An odd–even effect in the clearing temperatures is observed and the odd members display the higher values.     

聚甲基丙烯酸4［（4＇－硝基－1＇硫酰基苯）－1－羟烷氧基本基］酯的合成

new series of sulfur-contalning side chain liquid crystalline polymers were described. Mesomorphic side chains with methylene spacer in different length have been synthesized and their structures were identified by NMR, IR and MS.The liquid crystalline nature of the polymers was characterlzed by microscopy.The Polymers have liquid crystalline nature.     

聚甲基丙烯酸4［（4＇－硝基－1＇硫酰基苯）－1－羟烷氧基本基］酯的合成

聚甲基丙烯酸４［（４＇－硝基－１＇硫酰基苯）－１－羟烷氧基本基］酯的合成张维邦，蒋，许家瑞，曾汉民（中山大学材料科学研究所广州５１０２７５）关键词含硫液晶单元，侧链液晶高分子，液晶合成与表征侧链高分子液晶是高分子液晶的重要组成部分，是当前高分子科学中...     

Novel glassy nematic and chiral nematic oligomers derived from 1,3,5-cyclohexanetricarboxylic and (1R,3S)-( )-camphoric acids

Novel nematic and chiral nematic liquid crystals capable of vitrification have been synthesized using 1,3,5-cyclohexanetricarboxylic and (1R,3S)-(+)-camphoric acids as the base structures to which cyanotolan, cyanobiphenyl, methoxybiphenylbenzoate nematogenic groups, (S)-(-)-1-phenylethylamine and (S)-(+)-1,3-butanediol chiral moieties are attached. Once the glassy state is induced by quenching or controlled cooling from the isotropic state, these liquid crystals showed no detectable tendency towards crystallization upon heating through the glass transition temperature. In all cases, the ΔC_p and ΔH_c values resulting from the DSC heating scans are comparable to those previously reported for polymer analogues and other low molar mass glassy liquid crystals. In the nematic series with varying spacer lengths, both T_g and T_c are consistently lower than the linear polymer counterparts, in contrast to the siloxane-based systems. It was also demonstrated that cholesteric mesomorphism can be induced following one of the three approaches: chiral nematic mixture, chiral nematic cyclic cooligomer, and pendant nematogenic groups attached to a chiral ring.     

Mesogenic Unsymmetric dimers containing cholesteryl ester and tolane moieties

Among unsymmetric oligomesogens, chiral dimers formed by connecting a cholesteryl ester fragment with various aromatic mesogenic cores through a polymethylene spacer have been attracting much attention due to their remarkable thermal behaviour. In particular, dimers containing a diphenylacetylene segment having an alkoxy chain have shown interesting mesomorphic behaviour. In view of this a new series of unsymmetric dimers consisting of a diphenylacetylene moiety having an alkyl chain and a cholesteryl ester unit joined through a paraffinic spacer have been synthesized and their liquid crystalline properties characterized. The lengths of the central methylene spacer (C₃, C₄, C₅ and C₇) as well as that of the alkyl chain (n-butyl, n-pentyl, n-hexyl and n-heptyl) have been varied to establish structure-property relationships. These investigations have revealed that all the dimers exhibit smectic A, twist grain boundary and chiral neamtic (N*) phases with the exception of one of the dimers for which only the N* phase was observed. Some differences in the mesomorphic properties of the unsymmetric dimers containing odd or even parity methylene spacers have been observed. The majority of dimers having an even (C₄) parity paraffinic spacer show a blue phase while the dimers with odd (C₃, C₅ and C₇) parity spacers exhibit the chiral smectic (SmC*) phase. In some cases, the SmC* phase exists well below (-60°C) and above room temperature.     

Synthesis and characterization of liquid‐crystalline polyphosphonates containing disubstituted ferrocene esters as mesogens

A series of ferrocene‐containing liquid‐crystalline polyphosphonates with an even number of methylene groups are reported. All the polymers gave birefringent melts. The mesophase was identified as transparent with an increase in the spacer. The effects of pendant substitution and the spacer were studied with thermogravimetric analysis and differential scanning calorimetry. The effects of the phosphonate group in the spacer and the ferrocene ester group in the mesogen were examined. The presence of a steplike mesogenic structure and a pendant phenyl group in the spacer led to reductions in the glass‐transition and melting temperatures. The ferrocene moiety in the mesogen might be one of the reasons for the increased thermal stability and decreased liquid crystallinity. An energy‐minimized structure for the mesogenic and spacer segments was created with computer‐modeling programs, and it suggested the reason for the reductions in the glass‐transition and melting temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2256–2263, 2002     

Mesomorphic properties of liquid crystalline polysiloxanes and elastomers based on a tri-vinyl crosslinker

A series of crosslinked liquid crystalline polymers and the corresponding uncrosslinked liquid crystalline polymers were prepared by graft copolymerization; their liquid crystalline properties were characterized by DSC, POM and X-ray measurements. The results show that the crosslinking obtained in the isotropic state leads to a reduction of the clearing point (T_c) of the crosslinked polymers, as compared with the corresponding uncrosslinked polymers. The crosslinked polymers with low crosslinking density (P₁-P₇) exhibit nematic mesogenic phases, as do the uncrosslinked polymers. In contrast, a high crosslinking density leads to the crosslinked polymers P₈ and P₉ losing their thermotropic liquid crystalline phases; they instead exhibit stress-induced orientation.     

Thermal and topographical characterization of polyester- and styrene/acrylate-based composite powders by scanning probe microscopy

The thermal properties of two conventional polyester-based toners and a chemically prepared styrene/acrylate toner with different thermal histories were studied by scanning probe microscopy (SPM) and differential scanning calorimetry (DSC). The thermal transition temperatures detected by SPM agreed with the results of the DSC measurements. The validity of SPM for detecting thermal transitions was further confirmed by studying two amorphous reference polymers with different glass transition points (T_g) and three crystalline reference polymers with different melting points (T_m). When the toner sample was heated by the SPM probe above the glass transition temperature of the toner powder (T_probe > T_g), changes occurred in the surface topography and roughness causing different levels of local sintering of the particles. A set of roughness parameters calculated from the SPM image data were used to quantify the most essential features of toner surfaces. Environmental scanning electron microscopy (ESEM) was used to study the penetration depth of heat dissipated by the SPM probe. The probe-annealing was compared with oven-annealing in order to establish the effect of thermal history on the thermal properties of the materials.     

Melting and glass transitions in paraffinic and naphthenic oils

Naphthenic and paraffinic oils were analyzed by modulated differential scanning calorimetry (MDSC). The results showed several improvements in the analysis of thermal properties when compared with standard DSC. The glass transition temperature (T_g), the enthalpy relaxation at T_g, and the melting endotherms could be deconvoluted, and reversible melting could be identified. This allowed for an easier interpretation of the thermal properties of the oils. With MDSC, the T_gs in mineral oils were found to coincide with endothermic enthalpy relaxation, which is generally regarded as a melting endotherm with standard DSC. A decrease in heat capacity after T_g was attributed to the existence of rigid amorphous material. From Δc_p at T_g and the oil molecular weight, the number of repeat units in the oil chains was estimated at less than 20. The T_g of a hypothetical pure aromatic oil was found to be similar to that for petroleum asphaltenes, and that for a naphthenic oil of infinite molecular weight to be similar to that of petroleum resins.     

Gas permeability in rubbery polyphosphazene membranes

The synthesis, characterization, and gas permeability of 10 new polyphosphazenes has been studied. Additionally, the first gas permeation data has been collected on hydrolytically unstable poly[bis-(chloro)phosphazene]. Gases used in this study include CO₂, CH₄, O₂, N₂, H₂, and Ar. CO₂ was the most permeable gas through any of the phosphazenes and a direct correlation between the T_g of the polymer and CO₂ transport was noted with permeability increasing with decreasing polymer T_g. To a lesser degree, permeability of all the other gases studied also yielded increases with decreasing polymer T_g. The trend observed for these new polymers was further supported by published data for other phosphazenes. Furthermore, permeability data for all gases were found to correlate to the gas condensability and the gas critical pressures, except for hydrogen, suggesting that the nature of the gas is also a significant factor for permeation through rubbery phosphazene membranes. Ideal separation factors () for the CO₂/H₂ and CO₂/CH₄ gas pairs were calculated. For CO₂/CH₄, no increase in was observed with decreasing T_g, however increases in were noted for the CO₂/H₂ pair.     

Synthesis and thermal behaviour of salicylaldimine-based liquid crystalline symmetrical dimers

A series of symmetrical dimers consisting of salicylaldimine moieties connected by flexible alkylene central spacer via ether linkages has been synthesized. In order to validate the empirical rule suggested by Date et al. to account for the smectic behaviour of such dimers, the chain length of the terminal alkoxy chain has been kept constant (C₈) while the number of methylene units in the central spacer was varied from C₃ to C₁₁. Another aim of the present investigation was to understand structure-property relationship in these dimers in which the salicylaldimine mesogenic segment has been used for the first time in dimers. The mesomorphic behaviour of these dimers was evaluated using optical microscopy and differential scanning calorimetry and the structure of some of the mesophases has been further investigated with the help of X-ray diffraction. Our studies reveal that the dimers consisting of 3 to 8 methylene units in the flexible spacer show only smectic (smectic C and smectic A) phases. For the dimers containing 4, 6 and 8 methylene units in the central spacer, a unique filament growth pattern has been observed in the smectic A phase while cooling from the isotropic phase. The dimers containing of C₉ to C₁₁ methylene groups exhibit the nematic phase in addition to smectic modifications. This observation indicates that when the terminal chains are shorter than the spacer, the tendency to form smectic phases is not fully extinguished but is perhaps reduced.