Low-temperature heat capacity and standard molar enthalpy of formation of 9-fluorenemethanol (C14H12O)

Low-temperature heat capacities of the 9-fluorenemethanol (C14H12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T = 78 K and T = 390 K. The solid-liquid phase transition of the compound has been observed to be T-fus = (376.567 +/- 0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be Delta(fus)H(m) = (26.273 +/- 0.013) kJ (.) mol(-1) and Delta(fus)S(m) = (69.770 +/- 0.035) J (.) K-1 (.) mol(-1). The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, Delta(c)U(C14H12O, s) = -(7125.56 +/- 4.62) kJ (.) mol(-1) and Delta(c)H(m)degrees(C14H12O, s) = -(7131.76 +/- 4.62) kJ (.) mol(-1), by means of a homemade precision oxygen-bomb combustion calorimeter at T = (298.15 +/- 0.001) K. The standard molar enthalpy of formation of the compound has been derived, Delta(f)H(m)degrees (C14H12O, s) = -(92.36 +/- 0.97) kJ (.) mol(-1), from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle. (C) 2004 Elsevier Ltd. All rights reserved.

Low-temperature heat capacity and thermodynamic properties of crystalline 2-chloro-5-trichloromethylpyridine

The low-temperature heat capacities of 2-chloro-5-trichloromethylpyridine were measured with a high-precision automated adiabatic calorimeter in the temperature range from 80 K to 345 K. A solid-liquid phase transition was observed from 318.57 K to 327.44 K with peak temperature 324.67 K; the molar enthalpy and entropy of phase transition, DeltaH(m) and DeltaS(m), were determined to be 14.50 +/-0.02 kJ mol(-1) and 44.66 +/- 0.07 kJ K-1 mol(-1), respectively. The thermal stability was investigated through thermogravimetric analysis (TG). The TG and DTG results reveal that 2-chloro-5-trichloromethylpyridine starts to lose mass at 332 K due to evaporation and completely changes into vapour at 483 K under the present experimental conditions.

Investigation of thermodynamic properties of Co2O3 powder

The isobaric molar heat capacities of powder of Co2O3 were determined by an adiabatic calorimeter in the temperature range from 78 to 350 K. No phase transition takes place in this temperature range. The relationship of C-p,C-m with thermodynamic temperature T was established as C-p,C-m = -5 x 10(-6)T(3) + 0.0026T(2) + 0.0325T + 4.2592 (J K-1 mol(-1)), fitting coefficient R-2 = 0.9996. According to this relationship and the relationships between thermodynamic functions, the thermodynamic functions of powder of C2O3 were derived with 298.15 K as reference temperature. Thermal decomposition of Co2O3 powder was studied through thermogravimetry (TG). The possible mechanism of the thermal decomposition reaction was suggested according to the TG result. (C) 2003 Elsevier Science B.V. All rights reserved.

Heat capacities and thermodynamic functions of p-chlorobenzoic acid

The heat capacities of p-chlorobenzoic acid were measured in the temperature range from 80 to 580 K by means of an automatic adiabatic calorimeter equipped with a small sample cell of internal volume of 7.4cm(3). The construction and procedures of the calorimetric system were described in detail. The performance of this calorimetric apparatus was evaluated by heat capacity measurements on alpha-Al2O3. The deviations of experimental heat capacities from the corresponding smoothed values lie within +/-0.28 per cent, while the inaccuracy is within +/-0.40 per cent, compared with the recommended reference data in the whole experimental temperature range. A fusion transition at T = 512.280 K was found from the C-p-T curve of p-chlorobenzoic acid. The enthalpy and entropy of the phase transition, as well as the thermodynamic functions {G((T)) - G((298.15))}, {H-(T) - H-(298.15)} and {S-(T) - S-298.15}, were derived from the heat capacity data. The mass fraction purity of p-chlorobenzoic acid sample used in the present calorimetric study was determined to be 0.99935 by fraction melting approach. (C) 2002 Elsevier Science Ltd. All rights reserved.

Hole-transporting polymers containing carbazol-3,9-diyl and 1,4-phenylene fragments in the main chain

New carbazole-based polymers, which contain various content of electro-active fragments in the main chain connected via alkylene spacers, have been synthesized by Ni(0)-catalyzed Yamamoto-type aryl-aryl coupling reactions. These compounds represent amorphous materials of high thermal stability with glass-transition temperatures of 139-151 degrees C and thermal decomposition starting at temperatures above 400 degrees C. UV-vis absorption and photoluminescence emission spectra of the materials confirmed that the conjugated segments in the macromolecules are rather short.

Crystal structure and charge transfer energy of the vaterite-type orthoborate YBO3:Eu

Ligand-to-metal charge transfer energies of YBO3:Eu have been investigated from the chemical bond viewpoint. The chemical bond parameters, such as the covalency, the polarizability of the chemical bond volume, and the presented charge of the ligands in the chemical bond have been quantitatively determined based on the dielectric theory of complex crystal. We calculated the environmental factor (h(e)), which is the major factor influencing the charge transfer energy in the compounds. The calculated results show that the suitable group space of YBO3 is C2/c. The method provides us with a supplementary tool to judge the proper structure when the structure of the crystal has many uncertain space groups.

Novel temperature- and pH-responsive graft copolymers composed of poly(L-glutamic acid) and poly(N-isopropylacrylamide)

A series of novel temperature- and pH-responsive graft copolymers, poly(L-glutamic acid)-g-poly(N-isopropylacrylamide), were synthesized by coupling amino-semitelechelic poly(N-isopropylacrylamide) with N-hydroxysuccinimide-activated poly(L-glutamic acid). The graft copolymers and their precursors were characterized, by ESI-FTICR Mass Spectrum, intrinsic viscosity measurements and proton nuclear magnetic resonance (H-1 NMR). The phase-transition and aggregation behaviors of the graft copolymers in aqueous solutions were investigated by the turbidity measurements and dynamic laser scattering.

Novel pH- and temperature-responsive block copolymers with tunable pH-responsive range

A series of novel pH- and temperature-responsive diblock copolymers composed of poly(N-isopropylacrylamide) (PNIPAM) and poly[(L-glutamic acid)-co-(gamma-benzyl L-glutamate)] [P(GA-co-BLG)] were prepared. The influence of hydrophobic benzyl groups on the phase transition of the copolymers was studied for the first time. With increasing BLG content in P(GA-co-BLG) block, the thermal phase transition of the diblock copolymer became sharper at a designated pH and the critical curve of phase diagram of the diblock copolymer shifted to a higher pH region.

Synthesis and properties of soluble poly[bis(benzimidazobenzisoquinolinones)] based on novel aromatic tetraamine monomers

Four aromatic tetraamine monomers possessing flexible ether linkages were successfully synthesized by nucleophilic aromatic substitution of hydroquinone, 4,4'-dihydroxybiphenyl, 2,2'-bis(4-hydroxyphenyl)propane, and 2,7-dihydroxynaphthalene with 5-chloro-2-nitroaniline, followed by reduction, respectively. With these monomers, a new class of soluble poly[ bis(benzimidazobenzisoquinolinones)] was prepared by a one-step, high-temperature solution polycondensation. The resulting polymers were completely soluble in phenolic solvents and had high inherent viscosities ranging from 1.2 to 1.5 g dL(-1). These polymers had glass transition temperatures in the range of 427-449 degrees C. Thermogravimetric analysis showed that all polymers were thermally stable, with 5% weight loss recorded above 510 degrees C in nitrogen.

The synthesis and properties of meso-tetra(4-alkylamidophenyl)porphyrin liquid crystals and their Zn complexes

A series of novel, long-chain-substituted, porphyrin derivatives, meso-tetra (4-alkylamidophenyl) porphyrin ligands and their Zn complexes (alkyl = 8,10,12,14,16,18) were prepared by acylation of the amino groups of 5,10,15,20-tetra(4-aminophenyl)porphyrin by alkyl chloride. Mesomorphism was investigated by DSC, polarized optical microscopy (POM) and X-ray diffraction (XRD). Only ligands containing chains > 12 carbon atoms displayed liquid crystalline behaviour, which exhibited a high phase transition temperature and a broad mesophase temperature span, Zn complexes showed no liquid crystalline behaviour. Cyclic voltammetry, luminescence spectra and surface photovoltage spectroscopy revealed that covalent linking of an alkylamido group to the tetraphenylporphyrin molecule influences, significantly, the properties of the porphyrin macrocycle.

Preparation and characterization of poly (N-isopropylacrylamide)/polyvinylamine core-shell microgels

In this paper, well-defined temperature- and pH-sensitive core-shell microgels were synthesized by graft copolymerization in the absence of surfactant and stabilizer. The microgel particles consisted of poly (N-isopropylacrylamide (NIPAm)) core crosslinked with N, N'-methylene-bisacrylamide (MBA) and polyvinylamine (PVAm) shell. The effect of MBA content and NIPAm/PVAm ratio on microgel size was investigated. SEM showed that the microgels were spherical and had narrow particle-size distribution. TEM images of the microgels clearly displayed well-defined core-shell morphologies. Zeta-potential measurement further elucidated that the microgels possessed positively charged PVAm molecules on the microgel surface. Turbidity measurement and H-1-nuclear magnetic resonance (NMR) experiments indicated that the VPTT of microgels was the same as the LCST of PNIPAm.

Synthesis and Application of Thiadiazoloquinoxaline-Containing Chromophores as Dopants for Efficient Near-Infrared Organic Light-Emitting Diodes

series of a donor-acceptor-donor type of near-infrared (NIR) fluorescent chromophores based on [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ) as an electron acceptor and triphenylamine as an electron donor are synthesized and characterized. By introducing pendent phenyl groups or changing the pi-conjugation length in the TQ core, we tuned tile energy levels of these chromophores, resulting in the NIR emission in a range from 784 to 868 nm. High thermal stability and glass transition temperatures allow these chromophores to be used as dopant emitters, which can be processed by vapor deposition for the fabrication of organic light-emitting diodes (OLEDs) having the multilayered structure of ITO/MoO3/NPB/Alq(3):dopant emitter/BCP/Alq(3)/LiF/Al. The electroluminescence spectra of the devices based on these new chromophores cover a range from 748 to 870 nm. With 2 wt % of dopant 1, the LED device shows an exclusive NIR emission at 752 nm with the external quantum efficiency (EQE) as high as 1.12% over a wide range of current density (e.g., around 200 mA cm(-2)).

Nonconjugated Carbazoles: A Series of Novel Host Materials for Highly Efficient Blue Electrophosphorescent OLEDs

A series of carbazole derivatives was synthesized and their electrical and photophysical properties were investigated. It is shown that the triplet energy levels of these hosts are higher than that of the most popular blue phosphorescent material iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C-2'] picolinate (FIrpic) and the most extensively used phosphorescent host material 4,4'-N,N'-dicarbazole-biphenyl (CBP). These new host materials also showed good thermal stability and high glass transition temperatures (T-g) ranging from 78 to 115 degrees C as the linkage group between the carbazoles was altered. Photophysical measurements indicate that the energy transfer between these new hosts and FIrpic is more efficient than that between CBP and FIrpic. Devices incorporating these novel carbazole derivatives as the host material doped with FIrpic were fabricated with the configurations of ITO/NPB (40 nm)/host:FIrpic (30 nm)/BCP (15 nm)/AlQ (30 nm)/LiF (1 nm)/Al (150 nm). High efficiencies (up to 13.4 cd/A) have been obtained when 1,4-bis (4-(9H-carbazol-9-yl)phenyl)cyclohexane (CBPCH) and bis(4-(9H-carbazol-9-yl)phenyl) ether (CBPE) were used as the host, respectively.

Polyimides Derived from 1,4-Bis [3-oxy-(N-aminophthalimide)] Benzene

A novel diamine, 1,4-bis [3-oxy-(N-aminophthalimide)] benzene (BOAPIB), was synthesized from 1,4-bis [3-oxy-(N-phenylphthalimide)] benzene and hydrazine. Its structure was determined via IR, H-1 NMR, and elemental analysis. A series of five-member ring, hydrazine-based polyimides were prepared from this diamine and various aromatic dianhydrides via one-step polycondensation in p-chlorophenol. The inherent viscosities of these polyimides were in the range of 0.17-0.61 dL/g. These polymers were soluble in polar aprotic solvents and phenols at room temperature. Thermogravimetric analysis (TGA) showed that the 5% weight-loss temperatures of the polyimides were near 450 degrees C in air and 500 degrees C in nitrogen. Dynamic mechanical thermal analysis (DMTA) indicated that the glass-transition temperatures (T(g)s) of these polymers were in the range of 265-360 degrees C. The wide-angle X-ray diffraction showed that all the polyimides were amorphous.

Macrocycle-Terminated Core-Cross-Linked Star Polymers: Synthesis and Characterization

We have synthesized macrocyclic polystyrene- (PS-) terminated PS star polymers via a core-cross-linking approach in this work. A tadpole-shaped macrocyclic PS-linear-PS copolymer was synthesized at first via click chemistry and ATRP polymerization method. The "living" ATRP initiating chain-ends of the tadpole-shaped copolymers were linked together via ATRP polymerization with divinylbenzene to form a core-cross-linked macrocyclic star polymer. The number of arms attached to the macrocyclic star polymers was measured with NMR. and absolute molecular weights with gel permeation chromatography (GPC) with multiangle laser light scattering detector. These macrocyclic star polymers had a highly cross-linked core and many radiating arms. The shorter tadpole-shaped precursors caused core-cross-linked star polymers with higher molecular weights and more arm numbers. The macrocycle-terminated core-cross-linked star polymers showed two glass transition temperatures, one arising from the linear branches and another from the macrocycles.