Hot-stage Polarizing Optical Microscopy Research Articles

STUDIES ON ODD-EVEN EFFECT OF METHYLENE SPACERS IN POLY(PYROMELLITIMIDE-URETHANE)S

Three series of poly(pyromellitimide-urethanes)s were synthesized from various N,N′ -bis(ω-hydroxyalkyl)pyromellitimides (HAPMIs) and various dicarbooxyloxyl diazides namely terephthaloyl diazide (TPDA), 4,4′ -diphenyldiacid azide (BPDAA) and 4,4′ -azobenzenediacid azide by solution polycondensation in DMSO at 75°C in the presence of di-n-butyltin dilaurate as catalyst. The polymers were characterized by elemental analysis,IR, 1H and 13C-NMR and X-ray diffraction analysis. Thermalstability and phase transition behavior were studied by TGA, DSC, and hot-stage optical polarized microscopy (HOPM). Tg values decrease linearly as the number of methylene spacer increases while Tm shows odd-even effect. In a given series, polymers with even number of methylene spacers possess higher Tm values than the neighboring polymers with odd number of methylene spacers and thermal stability decreases with increase in number of methylene spacers. Thermal stability is also influenced by the aromatic segment present in the polymer backbone, order being : phenyl > biphenyl > azobenzene.

Studies on the odd-even effect of methylene spacers in poly(pyromellitimide-ester)s

Three series of poly(pyromellitimide-ester)s were synthesized from various N,N′-bis(ω-hydroxyalkyl)pyromellitimides (HAPMIs) by melt condensation with dicarboxylic acids, including terephthalic acid (TPA), 4,4′-biphenyldicarboxylic acid (BPDA), and 4,4′-azobenzenedicarboxylic acid (ABDA). Polymers were characterized by elemental analysis, solubility, inherent viscosity, spectra (IR, 1H-NMR, 13C-NMR), and X-ray diffraction (XRD). Thermal stability and phase transition behaviour were evaluated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and hot-stage optical polarized microscopy (HOPM). The d-spacings, calculated from XRD data, showed an odd-even effect with varying numbers of methylene spacers. Crystallinity of polymers decreased in the following order: azobenzene > biphenyl > phenyl polymers. Similarly, DSC-obtained melting temperatures (Tm's) showed an odd-even effect, and glass transition temperatures (Tg's) decreased with increasing numbers of methylene spacers. Thermal stability decreased as methylene chain length increased. Thermal stability of polymers occurred in the following order: phenyl > biphenyl > azobenzene polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1755–1761, 1999

Synthesis, characterization and thermal behaviour of poly(pyromellitimide-ester)s and (imide-urethane)s containing azobenzene units

Two new series of poly(pyromellitimide-ester)s and (imide-urethane)s were synthesized from N,N′-bis(ω-hydroxyalkyl)pyromellitimides (HAPMIs) with 4,4′-azobenzenedicarboxylic acid by melt polycondensation, and HAPMIs with 4,4′-azobenzenedicarboxylicacid azide by solution polycondensation, respectively. The polymers were characterized by elemental analysis, IR, 1H and 13C NMR and X-ray diffraction analysis. The d-spacings calculated for poly(imide-ester)s show an odd–even effect. The thermal stability and phase transition behaviour were studied by TGA, differential scanning calorimetry (DSC) and hot-stage optical polarized microscopy (HOPM). Poly(imide-ester)s show higher Tg and Tm values than the corresponding poly(imide-urethane)s. Tg values decrease linearly as the number of methylene spacer increases, while Tm shows odd–even effect. Poly(imide-ester)s show higher thermal stability than the corresponding poly(imide-urethane)s, and in the given series thermal stability decreases with an increase in the number of methylene spacers.

Studies on poly(imide-ester)s and poly(imide-urethane)s containing pyromellitimide units

Two new series of poly(imide-ester)s and poly(imide-urethane)s have been synthesized from various N,N′-bis(ω-hydroxyalkyl)pyromellitimides (HAPMIs). The poly(imide-ester)s were prepared from terephthalic acid with HAPMIs by melt polycondensation while poly(imide-urethane)s were obtained from HAPMIs with terephthaloyl diazide by solution polycondensation in DMSO using di-n-butyltin dilaurate at 75°C. Synthesized polymers were characterized by elemental analysis, solubility, inherent viscosity, IR, 1H and 13C NMR and X-ray diffraction studies. Thermal stability and phase transition behaviour were evaluated by TGA, DSC and hot-stage optical polarized microscopy (HOPM). From X-ray diffraction studies d spacings were calculated for poly(imide-ester)s and d spacings showed an odd–even effect with varying number of methylene spacers. Similarly Tm values obtained by DSC analysis, showed an odd–even effect. Thermal stability decreases as methylene chain length increases. © 1998 Society of Chemical Industry

Synthesis, Structure, and Thermotropic Mesomorphism of Layered N-Alkylpyridinium Tetrahalopalladate(II) Salts

Two homologous series of N-alkylpyridinium salts, [Cn-Py]2[PdX4] (n = 12, 14, 16, 18; X = Cl, Br), have been synthesized, and their thermal behavior has been studied by differential scanning calorimetry and hot-stage polarizing optical microscopy. Except for the substances with n = 12, all the materials show thermotropic polymorphism. The crystal structures of [C12-Py]2[PdCl4], [C16-Py]2[PdCl4], and [C16-Py]2[PdBr4] have been solved. All three complex salts crystallize in the triclinic space group P1̄. Crystal packing reveals layered structures with alternating polar and apolar sublayers, where each [PdX4]2- anion is sandwiched between two antiparallel pyridinium cations. Alkyl chains are highly interdigitated and tilted with respect to the layer normal. The structural characterization of the [Cn-Py]2[PdX4] (n = 16, 18; X = Cl, Br) salts has been achieved also through variable-temperature powder X-ray diffraction. The [PdCl4]2- salts undergo transitions to a second crystalline phase and then to an ordered and a disordered smectic phase. The latter are assigned to single-layered smectic-E and partially bilayered smectic-Ad phases, respectively. On warming, the [PdBr4]2- analogues only show the smectic-Ad phase, preceded by a crystalline phase very similar to the room-temperature solid phase. The relative importance of hydrogen bonding throughout the sequence of structural changes is briefly addressed.