Heat capacities and entropies of linear,aliphatic polyesters

New measurements of the heat capacity in the melt of poly(trimethylene succinate) (PTMS), poly(trimethylene adipate) (PTMA), and poly(hexamethylene sebacate) (PHMS) from 310 to 400 K are presented. Based on these data and literature data on eight other molten polylactones and poly(ethylene sebacate) (PES), an addition scheme is developed for linear, aliphatic polyesters that leads to the equation: which represents the ATHAS-recommended melt heat capacities for all linear polyesters. Combining previously discussed solid heat capacities, derived from an approximate frequency spectrum, with the new liquid heat capacities, the various thermodynamic functions (enthalpy, entropy, and Gibbs function) could be derived using the ATHAS computation scheme. The average value of residual entropy at zero kelvin of 5.3 ± 1.8 J/(K mol) per mobile bead for glassy linear polysters was found to be somewhat higher than for many other polymers in the data bank, but closer to that observed for linear, aliphatic polyamides. The phase transitions of PTMS, PTMA, and PHMS are also analyzed using the quantitative baselines available from the heat capacity study.     

Heat capacities and entropies of liquid,high-melting-point polymers containing phenylene groups (PEEK,PC, and PET)

The heat capacity at constant pressure of liquid PEEK, poly(oxy-1,4-phenylene-oxy-1,4-phenylene-carbonyl-1,4-phenylene), has been measured by scanning calorimetry from 420 to 680 K, and that of PC, poly(4,4′-isopropylidenediphenylene carbonate), from 325 to 610 K. These new data were combined with data-bank data for PC and PET, poly(ethylene terephthalate), over wide temperature ranges. An addition scheme for liquid heat capacities of similar macromolecules has been obtained. In addition, values of absolute entropy, residual entropy for the glassy state, enthalpy, and Gibbs function are estimated for these three polymers. Both melting and glass transition temperatures have been confirmed. The heat capacity increases at the glass transition temperature have been determined by making use of previously calculated solid-state heat capacities.     

Heat capacities of liquid polycyclic aromatic hydrocarbons

Liquid heat capacities of 14 aromatic hydrocarbons were measured using a DSC calorimeter. Measurements were performed in the temperature range 100 K above the melting temperature of each hydrocarbon. The lowest and highest temperatures considered were respectively 303 and 692 K. Experimental results were correlated using Benson's group contribution approach. The group parameters determined allow the experimental results to be represented to within 2%.     

Calculation of absolute molecular entropies and heat capacities made simple

We propose a fully-automated composite scheme for the accurate and numerically stable calculation of molecular entropies by efficiently combining density-functional theory (DFT), semi-empirical methods (SQM), and force-field (FF) approximations. The scheme is systematically expandable and can be integrated seamlessly with continuum-solvation models. Anharmonic effects are included through the modified rigid-rotor-harmonic-oscillator (msRRHO) approximation and the Gibbs–Shannon formula for extensive conformer ensembles (CEs), which are generated by a metadynamics search algorithm and are extrapolated to completeness. For the first time, variations of the ro-vibrational entropy over the CE are consistently accounted-for through a Boltzmann-population average. Extensive tests of the protocol with the two standard DFT approaches B97-3c and B3LYP-D3 reveal an unprecedented accuracy with mean deviations <1 cal mol⁻¹ K⁻¹ (about <1–2%) for the total gas phase molecular entropy of medium-sized molecules. Even for the hardship case of extremely flexible linear alkanes (C₁₄H₃₀–C₁₆H₃₄), errors are only about 3 cal mol⁻¹ K⁻¹. Comprehensive tests indicate a relatively strong variation of the conformational entropy on the underlying level of theory for typical drug molecules, inferring the complex potential energy surfaces as the main source of error. Furthermore, we show some application examples for the calculation of free energy differences in typical chemical reactions.

A novel scheme for the automated calculation of the conformational entropy together with a modified thermostatistical treatment provides entropies with unprecedented accuracy even for large, complicated molecules.     

Heat capacities and phase transitions of the antiferroelectric liquid crystals MHPOBC and MHPOCBC

Heat capacities of the antiferroelectric liquid crystals 4-(1-methylheptyloxycarbonyl)phenyl4-octyloxybiphenyl-4-carboxylate (MHPOBC) and 4-(1-methylheptyloxycarbonyl)phenyl4-octylcarboxybiphenyl-4-carboxylate (MHPOCBC), have been measured with an adiabatic calorimeter between 350 and 460 K. MHPOBC showed three smectic subphases (ferrielectric C*, ferroelectric C* and a fancy phase C*) between antiferroelectric smectic C* and paraelectric gamma alpha smectic A, while MHPOCBC exhibited only one subphase (smectic C*). These phases are clearly discriminated by the existence of phase transitions. The enthalpies and entropies gained at the respective phase transitions were very small. A much larger phase transition from smectic A to isotropic liquid was also observed in both compounds. A alpha     

Heat capacities of perfluoropolyethers

The heat capacities at constant pressure of liquid perfluoropolyethers with different chain structures were determined above the glass transition temperature up to 480 K by means of differential scanning calorimetry (DSC). The group contributions of the  O , CF₂ , and  CF(CF₃) were calculated as a function of the temperature. Anomalous behavior of ethereal oxygen in a perfluorinated chain, as previously found for group contributions to the glass transition and to the vaporization energy, was observed also for heat capacity where the oxygen contribution is consistently lower for perfluorinated polyoxides in comparison to the hydrogenated homologous. The jump in c_p at the glass transition follows a regular behavior in the sense that ΔC_p/beadmole is within the average range found by Wunderlich for the majority of polymers. Moreover, data obtained in the present work allow the prediction of c_p of perfluoropolyethers of whatever structure between T_g and 480 K. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2073–2082, 1997     

Heat capacities of linear macromolecules

The heat capacity of liquid selenium was measured from 500 K to 700 K. Three commercial dynamic differential calorimeters were used for the evaluation (du Pont, Mettler, Perkin-Elmer). Comparison with limited literature data by adiabatic calorimetry shows that all three instruments give data of better than ± 3 % accuracy. Differences among the instruments are thus mainly in the convenience of sample handling and calibration. The heat capacity measured shows a decreasing trend with increasing temperature, opposite to synthetic linear macromolecules.

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Zusammenfassung Die Wärmekapazität von flüssigem Selen wurde zwischen 500 und 700 K gemessen. Drei handelsübliche dynamische Differentialkalorimeter wurden zur Bewertung eingesetzt (du Pont, Mettler, Perkin-Elmer). Der Vergleich mit einigen Literaturangaben bezüglich adiabatischer Kalorimetrie zeigt für alle drei Instrumente eine höhere Genauigkeit als ± 3 %. Der Unterschied zwischen den Instrumenten besteht demnach hauptsächlich in der Leichtigkeit der Probenbehandlung und der Eichung. Die gemessene Wärmekapazität zeigt eine Abnahme mit steigender Temperatur, im Gegensatz zu synthetischen linearen Makromolekülen.

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Résumé On a mesuré la chaleur spécifique du sélénium liquide entre 500 et 700 K, à l'aide de trois analyseurs calorimétriques différentiels commerciaux (Du Pont, Mettler, Perkin-Elmer). La comparaison avec les données restreintes de la littérature, obtenues par calorimétrie adiabatique, a montré que les trois instruments donnent des résultats dont l'exactitude est meilleure que ± 3 %. Ainsi, les différences entre les instruments résident surtout dans la commodité de manipulation des échantillons et d'étalonnage. La chaleur spécifique ainsi mesurée tend à dimineur quand la température augmente, contrairement aux macromolécules synthétiques linéaires.

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500– 700 K. — , — . , , ±3%. , . , .

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Help by the du Pont Instruments Division, Wilmington, Delaware, in acquisition and operation of the du Pont 900 system is gratefully acknowledged.Thanks are expressed to Mr. H. J. Hoehn and to the Mettler, Instrument Corporation, Hightstown, N.J., for the opportunity to use and evaluate the TA 2000 system; and to Mr. G. Widmann of Mettler for the data used in this paper. Appreciation is also expressed to Dr. A. P. Gray, R. L. Fyans and the Perkin — Elmer Corporation, Norwalk, Conn. for their assistance in setting up the DSC-2 and providing us with the digital data recording facilities. This study was sponsored in part by a grant from the National Science Foundation (GH 42634X).     

Reaction of methanol with polychloroethylenes

Summary A new reaction between methanol and polychloroethylenes was discovered; it results in the formation of chloroallyl alcohols.     

Heat capacities and thermodynamic properties of MgNDC

One-three-dimensional metal-organic frameworks Mg_1.5(C₁₂H₆O₄)_1.5(C₃H₇NO)₂ (MgNDC) has been synthesized solvothermally and characterized by single crystal XRD, powder XRD, FT-IR spectra. The low-temperature molar heat capacities of MgNDC were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 205 to 470 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range. The thermodynamic parameters of MgNDC such as entropy and enthalpy relative to reference temperature of 298.15 K were derived based on the above molar heat capacities data. Moreover, the thermal stability and decomposition of MgNDC was further investigated through thermogravimetry (TG)?Cmass spectrometer (MS). Three stages of mass loss were observed in the TG curve. TG?CMS curve indicated that the oxidative degradation products of MgNDC are mainly H₂O, CO₂, NO, and NO₂.     

甲氰菊酯的热容及热力学性质的研究

采用精密自动绝热量热测量了自已合成并提纯到0.9916(摩尔分数)的甲氰菊酯在80~400K温区的热容.在此温区发现一固液熔化相变.其熔化温度、摩尔熔化焓、摩尔熔化熵分别为:(322.476^+~-0.012)K,(18.57^+~-0.29)kj.mol^-^1,(57.59^+~-1.01)J.K^-^1.mol^-^1.报道了该物质每隔5K的热力学函数值,用热重法研究了该化合物的热分解,对试样的化学纯度进行了量热研究。     

Heat capacities and thermodynamic properties of MgBTC

A novel two-dimensional metal organic framework MgBTC [MgBTC(OCN)₂·2H₂O, where BTC = 1,3,5-benzenetricarboxylate] has been synthesized solvothermally and characterized by single crystal XRD, powder XRD, FT-IR spectra. The low-temperature molar heat capacities of MgBTC were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 190 to 350 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range. The thermodynamic parameters of MgBTC such as entropy and enthalpy relative to reference temperature of 298.15 K were derived based on the above molar heat capacities data. Moreover, the thermal stability and decomposition of MgBTC was further investigated through thermogravimetry (TG)-mass spectrometer (MS). Four stages of mass loss were observed in the TG curve. TG-MS curve indicated that the products of oxidative degradation of MgBTC are H₂O, N₂, CO₂ and CO. The powder XRD showed that the mixture after TG contains MgO and graphite.     

Heat capacities of some phthalate esters

Isobaric heat capacities C _p in the liquid phase of dimethyl phthalate, diethyl phthalate, dibutyl phthalate, bis(2-ethylhexyl) phthalate, and benzyl butyl phthalate were measured by commercial SETARAM heat conduction calorimeters. Results obtained cover the following temperature range: dimethyl phthalate 283 to 323 K, diethyl phthalate 306 to 370 K, dibutyl phthalate 313 to 447 K, bis(2-ethylhexyl) phthalate from 313 to 462 K, benzyl butyl phthalate from 313 to 383 K. The heat capacity data obtained in this work were merged with available experimental data from literature, critically assessed and sets of recommended data were developed by correlating selected data as a function of temperature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Heat capacities of crystalline tetraalkylammonium salts

The behavior of crystalline tetraalkylammonium salts at 290–350 K was studied by differential scanning calorimetry. For tetraethyl- and tetrabutylammonium bromides (Et₄NBr and Bu₄NBr), the experimental heat capacities agreed well with the literature values. For tetrahexyl-, tetraheptyl-, and tetraoctylam-monium bromides (Hex₄NBr, Hep₄NBr, and Oct₄NBr), phase transitions were found between crystal modifications whose characteristic temperatures depended significantly on the size of the cation. Empirical equations for the temperature dependences of the heat capacities of the salts within the ranges of homogeneous equilibrium phases were derived.     

Heat capacities and thermodynamic properties of chrysanthemic acid

The heat capacities of chrysanthemic acid in the temperature range from 80 to 400 K were measured with a precise automatic adiabatic calorimeter. The chrysanthemic acid sample was prepared with the purity of 0.9855 mole fraction. A solid-liquid fusion phase transition was observed in the experimental temperature range. The melting point, T _m, enthalpy and entropy of fusion, Δ_fus H _m, Δ_fus S _m, were determined to be 390.741±0.002 K, 14.51±0.13 kJ mol^-1, 37.13±0.34 J mol^-1 K^-1, respectively. The thermodynamic functions of chrysanthemic acid, H _(T)-H_(298.15), S _(T)-S_(298.15) and G _(T)-G ₍₂₉₈.₁₅₎ were reported with a temperature interval of 5 K. The TG analysis under the heating rate of 10 K min^-1 confirmed that the thermal decomposition of the sample starts at ca. 410 K and terminates at ca. 471 K. The maximum decomposition rate was obtained at 466 K. The purity of the sample was determined by a fractional melting method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Heat capacities,third-law entropies and thermodynamic functions of the negative thermal expansion material Zn2GeO4 from T=(0 to 400) K

The molar heat capacity of Zn₂GeO₄, a material which exhibits negative thermal expansion below ambient temperatures, has been measured in the temperature range 0.5⩽(T/K)⩽400. At T=298.15 K, the standard molar heat capacity is (131.86 ± 0.26) J · K⁻¹ · mol⁻¹. Thermodynamic functions have been generated from smoothed fits of the experimental results. The standard molar entropy at T=298.15 K is (145.12 ± 0.29) J · K⁻¹ · mol⁻¹. The existence of low-energy modes is supported by the excess heat capacity in Zn₂GeO₄ compared to the sums of the constituent binary oxides.     

Heat capacities and thermodynamic functions of d-ribose and d-mannose

The heat capacities of d-ribose and d-mannose have been studied over the temperature range from 1.9 to 440 K for the first time using a combination of Quantum Design Physical Property Measurement System and a differential scanning calorimeter. The purity, crystal phase and thermal stability of these two compounds have been characterized using HPLC, XRD and TG–DTA techniques, respectively. The heat capacities of d-Mannose have been found to be larger than those of d-ribose due to its larger molecular weight, and the solid–liquid transition due to the sample melting has also been detected in the heat capacity curve. The heat capacities of these two compounds have been fitted to a series of theoretical models and empirical equations in the entire experimental temperature region, and the corresponding thermodynamic functions have been derived based on the curve fitting in the temperature range from 0 to 440 K. Moreover, the phase transition enthalpy and melting temperature of these two compounds have also been determined from the heat flows obtained in DSC measurements.

     

Heat capacities of liquids linear aliphatic polyoxides

Heat capacities at constant pressure of liquid polyoxymethylene (430-540 K) and polyoxyethylene (330-430 K) have been measured by scanning calorimetry. These new data are discussed together with the heat capacity of polyethylene and other linear, aliphatic polyoxides to arrive at a wide-range addition scheme for heat capacities. Values of absolute entropy, enthalpy, and Gibbs free energy are estimated. The new data are offered as “Recommended Data 1984” in our ATHAS Data Bank.     

Heat capacities of aqueous solutions containing diethanolamine and N-methyldiethanolamine

In this work, we present new results for heat capacities of aqueous mixtures of diethanolamine with N-methyldiethanolamine over the temperature range (303.2 to 353.2) K with a differential scanning calorimeter. For mole fractions of water ranging from 0.2 to 0.8, 16 concentrations of the (DEA + MDEA + water) systems were investigated. For the binary system, (DEA + MDEA), heat capacities of nine concentrations were also measured. A Redlich–Kister-type equation for representing excess molar heat capacity was applied to correlate the measured C_p of aqueous alkanolamine solutions. For a total of 176 data points for the (DEA + MDEA + water) system, the overall average absolute percentage deviation of the calculations are 16.5% and 0.2% for the excess molar heat capacity and the molar heat capacity, respectively. The heat capacities presented in this study are, in general, of sufficient accuracy for most engineering-design calculations.     

ViscosityB-coefficients,structural entropies and heat capacities,and the effects of ions on the structure of water

The water-structural contributions to the entropies and heat capacities of hydration of over 120 ions and the viscosity B-coefficients of nearly 80 aqueous ions are tabulated and correlated. B-coefficients for many more ions are predicted from this relationship and from their dependence on ionic size and charge. The structural entropies determine a unique scale of water structure making and breaking by the ions.