Synthesis and thermal behaviour of model compounds for thermotropic main chain polyesters (original) (raw)
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Macromolecules, 1997
The effect of flexible spacer length on the phase transitions and mesophase structures of main-chain thermotropic liquid-crystalline polyesters having bulky pendent side groups was investigated using differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and polarizing optical microscopy (POM). For the investigation, a homologous series of poly[(phenylsulfonyl)-p-phenylene alkylenebis(4-oxybenzoate)]s (PSHQn) having varying lengths (n) of methylene groups of flexible spacers (n) 3-12) were synthesized in our laboratory. Using POM we observed that all PSHQn synthesized, with the exception of PSHQ3, have only a schlieren-textured nematic mesophase at temperatures between a glass transition temperature (or melting point) and the isotropization temperature; the nematic-isotropic transition temperature exhibits odd-even fluctuation with the number of methylene groups of the flexible spacer. We found that the isotropization enthalpy and isotropization entropy for PSHQn do not follow a linear relationship with the number of methylene groups when the flexible spacer length becomes shorter than 7, which deviates from the findings for linear main-chain TLCPs reported in the literature. We ascribe this difference to the presence of bulky pendent arylsulfonyl side groups in the main-chain of PSHQn. We found from both DSC and WAXD that (i) PSHQn having odd numbers (5-11) of methylene groups exhibit a glassy nematic mesophase, while PSHQ3, having three methylene groups, has no liquid crystallinity, becoming an amorphous polymer with a glass transition temperature of 129°C, and (ii) among the PSHQn having even numbers (4-12) of methylene groups, PSHQ4 showed the highest degree of ordering in the crystalline structure. WAXD of PSHQn melt-drawn fibers showed an odd-even fluctuation of chemical repeat unit d-spacing, very similar to that reported in the literature for linear main-chain TLCPs.
Thermotropic liquid-crystalline polymers: A new type of mesomorphic macromolecular system
1980
A new approach to the synthesis of thermotropic liquid-crystalline (LC) polymers is described based on the polymerization of monomers containing various mesogenic groups attached to the backbone chain by flexible polymethylene spacer groups. Dozens of new LC polymers are described, including derivatives of polymethacryloyl L-lysine, cholesteric esters of long-chain aminocarboxylic acids, and other aromatic polymers. Phase transition temperatures, heats of fusion, and x-ray structural analysis were evaluated. Polymers exhibiting spontaneous optical anisotropy in the glasslike, elastic, and fluid states are described, and schemes of molecular packing in the LC phase are proposed. We show the possibility of realizing smectic, nematic, and cholesteric types of structures in these thermotropic LC polymers. A n LC structure for various comblike copolymers not having mesogenic groups at every monomeric unit was detected. The role of specific interactions in side groups and their mobility in allowing for the LC structure are discussed, and the necessity of having particular conformations of the macromolecules is shown to provide the LC structure in films made from various solutions.
Journal of Polymer Science Part A: Polymer Chemistry, 1995
Two series of thermotropic liquid-crystalline polymers (TLCPs) were synthesized by reacting various dialkoxy terephthalate units with hydroquinone (HQ) and 2,6-naphthalene diol (Naph). The dialkoxy terephthalate moieties used in this study include 2,5-diethoxyterephthalate, 2,5-dibutoxyterephthalate, and 2,5-dihexyloxy-terephthalate. All the TLCPs synthesized in this study formed nematic phases. The molecular motions according to the length of the dialkoxy side groups in the TLCPs were evaluated by 13 C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy. The thermal properties and molecular dynamics of the TLCPs are found to be affected by the length of the dialkoxy side group and the aromatic diol unit in the main chain. Further, the thermal behaviors, liquid crystalline mesophases, and degree of crystallinity of the two series of TLCPs, i.e., HQ-and Naph-TLCPs, are compared.
Journal of Polymer Science Part A: Polymer Chemistry, 1997
A series of wholly aromatic, thermotropic polyesters, derived from 3,3-bis (phenyl)-4,4-biphenol (DPBP), nonlinear 4,4-benzophenone dicarboxylic acid (4,4-BDA), and various linear comonomers, were prepared by the melt polycondensation reaction and characterized for their thermotropic properties by a variety of experimental techniques. The homopolymer of DPBP with 4,4-BDA had a fusion temperature (T f) at 265ЊC, exhibited a nematic phase, and had a liquid crystalline range of 105ЊC. All of the copolyesters of DPBP with 4,4-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), or 50 mol % terephthalic acid (TA), 2,6-naphthalenedicarboxylic acid (2,6-NDA) had low T f values in the range of 220-285ЊC, exhibited a nematic phase, and had accessible isotropization transitions (T i) in the range of 270-420ЊC, respectively. Their accessible T i values would enable one to observe a biphase structure. Each of the copolymers with HBA or HNA had a much broader range of liquid crystalline phase. In contrast, each of the copolymers with TA or 2,6-NDA had a relatively narrow range of liquid crystalline phase. Each of these polyesters had a glassy, nematic morphology that was confirmed with the DSC, PLM, WAXD, and SEM studies. As expected, they had higher glass transition temperatures (T g) in the range of 161-217ЊC than those of other liquid crystalline polyesters, and excellent thermal stabilities (T d) in the range of 494-517ЊC, respectively. Despite their noncrystallinity, they were not soluble in common organic solvents with the exception that the homopolymer and its copolymer with TA had limited solubility in CHCl 3. However, they were soluble in the usual mixture of p-chlorophenol/1,1,2,2-tetrachloroethane (60/40 by weight) with the exception of the copolymer with 2,6-NDA. ᭧ 1997
Pure and Applied Chemistry, 2000
A new field of physical chemistry of macromolecular compounds -physical chemistry of synthetic liquid-crys-. talline polymers, particularly, comb-.like polymers with mesogenic side..groups is considered. The classification of mesophase types of such polymers is given and the dependence of its structure on the chemical constitution of monomeric units is analized. The approaches to creation of liquid crystalline polymers with definite interval of existance and of mesophase type are demonstrated. Particular attention is paid to the structure and the optical properties (selective reflection of light) of cholesteric polymers. The formation of an intramo-. lecular liquid crystalline structure in solutions of polymers with mesogenic side groups is discussed.
Macromolecular Chemistry and Physics, 1994
The influence of replacing a methylene group in the middle of the side chain of alkoxy-substituted poly(p-phenylene terephthalate)s by an oxygen atom was investigated by differential scanning calorimetry (DSC), rheological measurements and X-ray diffraction. Due to the presence of the oxygen atom the side chains of the polymer with long side chains (PTA12(O)HQ) lose their ability to crystallize. Except for this difference and a shift of the transition temperatures to lower temperatures, this polymer shows a similar phase behaviour compared to the corresponding alkoxy-substituted polyester PTA12HQ. The polymer with short side chains, PTA6(O)HQ, shows a similar behaviour as the corresponding polymer without an extra oxygen atom, PTA6HQ. Only the transition to the nematic mesophase is shifted to lower temperatures.
Die Makromolekulare Chemie
The syntheses of a number of new comb-like polymers are described, which contain mesogenic groups as side branches presenting models of low-molecular liquid crystals of smectic type. The resulting polymers are capable to form an enantiotropic liquid crystalline phase, which may be defined as smectic, according to the terminology used for low-molecular liquid crystalline substances. The thermodynamic limits of the liquid crystalline state in these polymers were determined, which made it possible to define the liquid crystalline state as a thermodynamically stable phase with spontaneously appearing anisotropy of properties (in particular, the optical anisotropy). The characteristic feature of the structure of these polymers was found to be the layer order of side groups providingin combination with the packing of the mesogenic groupsthe possibility of liquid crystalline properties. Only the mesogenic groups take part in the formation of the crystalline packing in these polymers, whereas the methylene chains are in the amorphous phase together with the backbone chain. *) Part 2: V. P. Shibaev, R. V. Tal'rose, F. I. Karakhanova, N. A. Plate, J. Polym. Sci., Polym. Chem. Ed. 17, 1671 (1979).
Die Makromolekulare …, 1985
A theory of orientational ordering in the melts of comb-like polymers containing mesogenic groups in the side chains is proposed. A variant of the lattice method is used, which was developed in our previous publication for the analysis of the liquid-crystalline transition in thermotropic polymers with mesogenic groups in the main chain. A full phase diagram for the system under consideration is constructed and the properties of the corresponding phase transition are determined. It is shown that for polymers with mesogenic groups in the side chain the dependence of the behaviour of the macromolecular main chain on the ordering of the mesogenic groups is much weaker than in the case of linear polymers with mesogenic groups in the main chain.