Thermochemistry of the Binary System Nitrocellulose+2,6-dinitrotoluene

The mixing and melting enthalpy of the binary system nitrocellulose+2,6-dinitrotoluene was determined using the DSC method. The mixing enthalpy of the components was calculated. At the melting temperature the maximum value of the mixing enthalpy for the mole fractionx _w26DNT=0.607 is equal H ^M _max= −3.41 kJ mol⁻¹. Measurements of the melting process (second measurement) were conducted after a storage period of several days at room temperature. Analysis of the melting peaks shows that the melting process of 26DNT takes place in pores of the micro-fiber and bulk outside the fibers. In the case of a mass fraction of x _w26DNT>0.9 the melting process takes place in the bulk, which suggests that in the case of such concentrations separation of the micro-fibers occurs. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermochemistry of the binary system nitrocellulose+N-nitrodiethanolamine dinitrate

The melting and mixing enthalpy of the binary system nitrocellulose and N-nitrodiethanolamine dinitrate (DINA) was determined by DSC. The mixing enthalpy H _max^M = 1.95 kJ mol⁻¹ had maximum at mass fraction x _wDINA=0.46. The influence of samples storing on glass and endothermic transitions were studied. The temperature range of glass transition broadened with x _wDINA what proved the increase of samples heterogeneity. For x _wDINA≤0.750 no influence of samples storing on the phase changes was observed. The heat capacity change decreased and temperature range of glass transition increased for x _wDINA≤0.500 what indicated the reduction of glass phase fraction in studied samples.     

DSC studies on long-term properties of nitrocellulose and SYM-diphenylurea system

Long-term investigations of the phase structure and pore structure of nitrocellulose and sym-diethyldiphenylurea (C1) mixtures were conducted for samples with C1 mass fractions w _C1=0.5, 0.6 and 0.8. The distribution of pore sizes and the composition of the nitrocellulose matrix were determined based on the melting enthalpy of C1. The three kinds of pores was observed with the characteristic size of about 7, 14 and 28 nm. Long-term storage of mixtures caused an increase in size of the smallest pores and a decrease of C1 concentration in the nitrocellulose matrix. The mechanism of changes in pore sizes is presented in term of multi-sheet model of NC fiber. This revised version was published online in July 2006 with corrections to the Cover Date.     

Intermolecular interactions and phase equilibria in nitrocellulose - s-diethyldiphenylurea system

Values of the Flory-Huggins interaction parameters c were predicted on the base of mixing enthalpy H ^M for nitrocellulose-s-diethyldiphenylurea system. The phase diagram of the system and the glass transition temperature of mixtures T _g12 were estimated using calculated c parameters. The predicted glass transition temperatures were in accordance with values determined experimentally. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamic and kinetic behaviour of salicylsalicylic acid

The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10°C min^-1. The melting peak showed an onset at T _on = 144°C (417 K) and a maximum intensity at T _max = 152°C (425 K), while the onset of the glass transition signal was at T _on = 6°C. The melting enthalpy was found to be Δ_mH = 28.9±0.3 kJ mol^-1, and the heat capacity jump at the glass transition was ΔC _P = 108.1±0.1 J K^-1mol^-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol^-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as Δ_fH_m ^o(C₁₄H₁₀O₅, cr) = - (837.6±3.3) kJ mol^-1, by combustion calorimetry. This revised version was published online in August 2006 with corrections to the Cover Date.     

A study of enthalpic relaxation of a liquid crystal

A liquid crystal, BL038, which was observed not to crystallize, has a glass transition at 215 K and a nematic to isotropic transition at 380 K. Samples aged below the glass transition at various temperatures T _a, exhibited an endotherm at the transition which developed with extent of ageing time, t _a. We attribute this endotherm to the relaxation of the glass towards the equilibrium liquid. The progress of the relaxation process was measured using differential scanning calorimetry. On subsequent reheating, the aged glass showed an apparent shift in the glass transition to higher temperatures. The endotherm was used to define the extent of enthalpic relaxation and the maximum value observed was found to increase initially then decrease, with the extent of undercooling from the glass transition temperature, Δ T, passing through a maximum for a Δ T = 15 K. From the temperature dependence of the relaxation times, an apparent activation enthalpy for the relaxation process of 85 ± 10 kJ mol^-1 was determined. The small value of the activation enthalpy compared with that found in the ageing of polymers reflects differences in the molecular species involved in relaxation processes.     

Heat capacity and glass transition of ethylene oxide clathrate hydrate

The heat capacity of structure I ethylene oxide clathrate hydrate EO-6.86 H₂O was measured in the temperature range 6–300 K with an adiabatic calorimeter. The temperature and enthalpy of congruent melting were determined to be (284.11 ± 0.02) K and 48.26 kJ mol^–1, respectively. A glass transition related to the proton configurational mode in the hydrogen-bonded host was observed around 90 K. This glass transition was similar to the one observed previously for the structure II tetrahydrofuran hydrate but showed a wider distribution of relaxation times. The anomalous heat capacity and activation enthalpy associated with the glass transition were almost the same as those for THF-hydrate.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.Author for correspondence.     

Nitro- and fluoropolyformals. III. Copolyformals from mixtures of fluoro- and nitro-α,ω-diols

Polyformals of fluoro-, nitramine-, and C-nitrodiols show widely differing properties with respect to glass transition temperature, melting transition, and solubility. Polymers with desirable combinations of these properties, e.g., low T_g, high nitro content, and good solubility in polar solvents, were expected to result from acid-promoted copolycondensation of appropriate mixtures of diols with formaldehyde. A series of such condensations were carried out and the polymers obtained from binary mixtures of fluoro- and nitrodiols, different nitrodiols, and fluoro- or nitrodiols and carboranediols, were characterized by GPC, ¹H-NMR, and DSC analysis.     

Thermochemistry of the Binary System Nitrocellulose-s-Diethyldiphenylurea

A method of gelation enthalpy determination of nitrocellulose (NC)+s-diethyldiphenylurea (Centralite 1, C1) binary system was elaborated using the change of Centralite 1 melting enthalpy in the mixture. The heats of C1 melting together with gelation and dissolution of NC fibres were determined by DSC calorimetric methods. A sharp maximum of the gelation enthalpy for C1 mole fraction x _C1 ^max =0.555 suggests that the complex is very stable and one partly nitrated anhydroglucose ring is interacting with about 1.25 C1 molecules. The gelatinization enthalpy maximum equals =−4.59 kJ mol⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.     

The thermodynamic properties of polytetrafluoroethylene

Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ₃ of 54 K, and θ₁ of 250 K, and a full set of group vibrations. C_v to C_p conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10^?3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔC_p of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.     

Catalytic wet air oxidation of 2-nitrotoluidine and 2,4-dinitrotoluene

The rates of wet air oxidation of 2-nitrotoluidine and 2,4-dinitrotoluene in the presence of excess oxygen and at different temperatures and oxygen pressures was investigated. Oxidation experiments were carried out at temperatures between 180 and 225^oC and oxygen partial pressures of 1,0-3,0 MPa, in a 280 mL glass vessel-inserted stainless steel reactor. Copper sulfate (CuSO₄ .5H₂O) was used as a catalyst, and the effect of catalyst loading was studied by varying the concentration: 0.75, 2.5 and 25 mg/L as Cu²⁺. Addition of Cu²⁺ ions in the reaction media accelerated 2-nitrotoluidine oxidation nearly ten times even if it exists in trace amount in the reaction medium (0.75 ppm Cu²⁺). Unfortunately copper did not show catalytic effect for the oxidation of 2,4-dinitrotoluene. This revised version was published online in August 2006 with corrections to the Cover Date.     

Infrared spectroscopic studies of polymer transitions. III. Effects of sodium ion on glass transitions in styrene-based ionomers

The glass transition in styrene-based ionomers was investigated by means of infrared spectroscopy and differential scanning calorimetry (DSC). Transition temperatures were determined from the temperature dependence of the peak absorbances of the 1700 and 1745 cm^?1 bands. These transition temperatures agreed with glass transition temperatures (T_g) determined by DSC. With increasing degree of ionization, T_g and the enthalpy ΔH of the residual intermolecular hydrogen bonding increased. The values of T_g obtained were analyzed by the theory of Fox and Loshaek for the effect of crosslinks. It is concluded that sodium ions probably from ionic domains and act as crosslinks to reinforce the residual hydrogen bonding and may increase T_g. The absorbance at 1560 cm^?1 (ν_COO^?) did not change at T_g. This suggests that the glass transition observed here is not due to the onset of the mobility in ionic domains, as has been proposed for ethylene-based ionomers on the basis of dielectric measurements.     

The effect of soft-segment length and concentration on phase separation in segmented polyurethanes

Three series of polyurethanes, based on three polyols, diphenylmethane diisocyanate (MDI), and three chain extenders were synthesized. Polypropylene glycol (PPG) soft-segment length (MW 1000, 2000, and 3000), soft-segment concentration (30%, 50%, and 70%), and the type of chain extender (ethylene glycol, butane diol, and hexane diol) were varied and their effect on the amount of phase separation studied. Methods for assessing phase separation quantitatively, based on shifts of the glass transition temperature T_g and the enthalpy jump at the glass transition were tested. It was shown that they give incorrect results, especially with PPG 1000 as the soft segment. Dependence of the soft segment T_g on the polyol length was explained by the “network effect.” True phase mixing was found only with PPG 1000 series at low soft-segment concentration, whereas, no clear indication of the phase mixing with PPG 2000 and PPG 3000 based polyurethanes was observed.     

2,4-二硝基甲苯热解自催化特性鉴别及其热解动力学

为研究2,4-二硝基甲苯(2,4-DNT)的热危险性及其分解反应的特征, 利用差示扫描量热仪(DSC)对该物质进行了动态扫描测试, 得到其起始分解温度T₀范围为272.4-303.5℃, 分解热ΔH_d约为2.22 kJ·g^-1. 在此基础上, 采用瑞士安全技术与保障研究所提出的快速鉴别法(瑞士方法)及数值模拟技术, 对其分解反应的特性参数进行了推算, 结果表明其分解具有自催化性. 采用Malek法分析了该物质分解反应的最概然机理函数并得出了相关动力学参数, 表明其分解具有自催化性且符合Sestak-Berggren 双参数自催化模型(SB模型), 这与瑞士方法所得结论一致. 采用等温DSC测试获得了该物质的‘钟形’热解曲线, 从而验证了两种方法的结论.     

Thermoanalytical investigation of some alkaline earth hydroxide hydrates on application as latent heat storage materials

Owing to their high specific melting enthalpy and the range of the melting temperatures the alkaline-earth hydroxide hydrates Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O are promising latent heat storage materials. The investigations of the melting and solidification behaviour of Sr(OH)₂·8H₂O and its mixtures with Ba(OH)₂·8H₂O, which had been performed by means of DTA and DSC methods in the closed system with a constant gross composition lead to statements on the melting temperature and specific melting enthalpyvs. concentration. Theoretical storage densities of 532 MJ/m³ are obtained for the mixture of Ba(OH)₂·8H₂O and Sr(OH)₂·8H₂O (80/20) and a value of 655 MJ/m³ can be achieved for Sr(OH)₂·8H₂O. The kinetics of rehydration to the octahydrates has a great influence on the storage temperature and storage density.     

Solubility and Solution Thermodynamics of Some Sulfonamides in 1-Propanol + Water Mixtures

The solubilities of sulfadiazine (SD), sulfamerazine (SMR) and sulfamethazine (SMT) in some 1-propanol + water co-solvent mixtures were measured at five temperatures from 293.15 to 313.15 K over the polarity range provided by the aqueous solvent mixtures. The mole fraction solubility of all these sulfonamides was maximal in the 0.80 mass fraction of 1-propanol solvent mixture (δ _solv = 28.3 MPa^1/2) and minimal in water (δ = 47.8 MPa^1/2) at all temperatures studied. The apparent thermodynamic functions Gibbs energy, enthalpy, and entropy of solution were obtained from these solubility data by using the van’t Hoff and Gibbs equations. Apparent thermodynamic quantities of mixing were also calculated by using the ideal solubilities reported in the literature. Nonlinear enthalpy–entropy relationships were observed for these drugs in the plots of enthalpy versus Gibbs energy of mixing. The plot of ?_mix H° versus ?_mix G° shows different trends according to the slopes obtained when the mixture compositions change. Accordingly, the mechanism for the solution process of SD and SMT in water-rich mixtures is enthalpy driven, whereas it is entropy driven for SMR. In a different way, in 1-propanol-rich mixtures the mechanism is enthalpy driven for SD and SMR and entropy driven for SMT. Ultimately, in almost all of the intermediate compositions, the mechanism is enthalpy driven. Nevertheless, the molecular events involved in the solution processes remain unclear.     

Kinetics of the solvolysis of [Co(Rpy)4Cl4]+ with R = 4-t-Bu, 3-Me or 3-Et in mixtures of urea with water

Summary The kinetics of the solvolysis of complex ions trans-[Co(Rpy)₄Cl₂]⁺, with R = 4-t-Bu, 3-Me and 3-Et, have been investigated in mixtures formed by adding urea to water, which enhances the dielectric constant and decreases solvent structure. Differential effects of the changes in solvent structure on the initial and transition states are found to be important factors controlling changes in the rate constant with solvent composition. The variation of the enthalpy and the entropy of activation with solvent composition are contrasted with their variations found for the solvolysis of [Co(Rpy)₄Cl₂]⁺ in mixtures where solvent structure is enhanced by additions of a co-solvent to water. The application of a free energy cycle to the process of the initial state going to the transition state suggests that the Co³⁺ cation in the transition state is more stable than the Co³⁺ cation in the initial state in the water + urea mixtures.     

Epoxidation of bacterial polyesters with unsaturated side chains. II. Rate of epoxidation and polymer properties

Poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate)s (PHOUs) with controlled amounts of unsaturated repeating units were epoxidized to various extents with m-chloroperbenzoic acid (MCPBA) in homogeneous solution. The epoxidation reaction was second order, with an initial rate constant of 1.1 × 10⁻³Lmol^−1.s⁻¹ at 20°C, regardless of the unsaturated unit content in PHOU. No substantial change in either molecular weight or molecular weight distribution occurred as a result of epoxidation, but the melt transition temperature and enthalpy of melting both decreased as the unsaturated groups were increasingly converted into epoxide groups. In contrast, the glass transition temperature (T_g) increased by approximately 0.25°C for each 1 mol % of epoxidation, irrespective of the composition of the PHOU. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2381–2387, 1998     

Thermophysical properties of azomethine ether main-chain liquid crystalline polymers at pressures to 200 MPa

This article reports on an experimental investigation of the equation of state and the transition behavior of main-chain thermotropic liquid crystalline polymers over a wide temperature range, and at pressures to 200 MPa. The materials studied were a series of azomethine ether polymers. A varying number n (= 4, 7, 8, 9, 10 and 11) of methylene spacer units in the backbone provided systematic variation of the structure. Experimental techniques used included high-pressure dilatometry (PVT measurements) to 200 MPa, high-pressure differential thermal analysis, also to 200 MPa, and conventional (atmospheric-pressure) differential scanning calorimetry (DSC). The equation of state of the materials can be well represented by the Tait equation in distinct regions, separated by a glass transition, T_g(P), a first-order transition to a nematic state, T_k-n(P), and a first-order transition to an isotropic melt state T_c(P). The atmospheric pressure values of T_k-n and T_c decreased with increasing number of spacer units and showed a clear odd-even effect. T_g and T_k-n both increased with pressure. The pressure dependence of T_c could not be observed due to the onset of degradation in the same temperature region. On isobaric cooling at 3°C/min, the crystallization from the nematic state occurred a few tens of degrees below T_k-n. This supercooling was independent of pressure for some materials, while for others it increased with increasing pressure. The values of the enthalpy and entropy associated with the first-order transition into the nematic state were lower than those of typical isotropic polymers at their melting transitions. The transition enthalpy did not have any systematic variation with increasing number of spacer units. Values of the transition enthalpy calculated from the Ciapeyron equation did not always agree with the values measured by DSC. This may be due to the two-phase nature of the low-temperature state. At the transition to the isotropic state, the transition enthalpy at P = 0 decreased with n and showed an odd-even effect. © 1994 John Wiley & Sons, Inc.     

Simultaneous volume and enthalpy relaxation

The ratio between the relaxed enthalpy and volume (so-called aging modulus, K_a) was expressed in frame of the Tool-Narayanaswamy-Moynihan theory. The common case where various experimental arrangements are used for measuring these quantities was analyzed. It was found that relatively small differences between the conditions of enthalpy and volume relaxation experiments may cause a significant shift of observed K_a value. The sensitivity of K_a modulus to the difference between the enthalpy and volume relaxation conditions is significantly higher in the case of organic polymeric glasses in comparison with silicate and chalcogenide glasses. The reason for such grouping resides in higher values of glass transition temperature and lower values of activation enthalpy of inorganic glasses.