Concept of hard clusters in the interpretation of thermal and mechanical properties of polyurethane and polyurethane acrylate networks

Polyurethane (PU) and polyurethane acrylate (PUA) networks based on hydroxyl-terminated polycaprolactone (PCL), 1,3-bis-2,2′(2-isocyanatopropyl)benzene (m-TMXDI), trimethylolpropane (TMP) for PU or hydroxyethyl methacrylate (HEMA) for PUA were synthesized. Glass transition temperature, T_g, dynamic mechanical relaxation, α, and equilibrium tensile modulus, E′, were measured to compare the two kinds of networks. To explain thermal and mechanical properties of networks, the concept of hard clusters has been introduced. PU networks exhibit a single-phase structure with modulus and T_g dependent on the concentration of elastically active network chains (EANC) per unit volume calculated by considering hard crosslink clusters. The rigidity of the clusters comes from small diisocyanate and trimethylolpropane units connected by urethane bonds. They are embedded in a continuous soft phase of macrodiol urethane. Physical equivalence between several kinds of network models has been demonstrated for full conversion of isocyanate-alcohol reaction. PUA networks exhibit thermodynamically one-phase structures that become a two-phase structure for high molar mass of macrodiol when the molar fraction of isocyanate groups increases. For those networks, the calculated modulus considering clusters based on polyacrylate chains seems to be a good way to approach the experimental value of the equilibrium modulus. For the same molar ratio of OH to NCO groups the range of dynamic moduli is larger for PUA than for PU. This difference can be explained by a different concentration of crosslinks in the networks. © 1996 John Wiley & Sons, Inc.     

D2O–H2O solvent isotope effects on the volumetric properties of aqueous 1,3-dimethyl-2-imidazolidinone between (278.15 and 318.15) K

Densities of dilute solutions of 1,3-dimethyl-2-imiazolidinone in H₂O and D₂O, with the solute mole-fractions ranging up to 0.01, have been measured with an error of 1.5 · 10⁻⁵ g · cm⁻³ at (278.15, 288.15, 298.15, 308.15, 313.15, and 318.15) K and atmospheric pressure using a vibrating-tube densimeter. The partial molar volumes of the dissolved DMI (down to the infinite dilution) and solvent (H₂O or D₂O) as well as the excess molar volumes of the isotopically distinguishable solutions have been calculated. The effects of the solvent isotope substitution, solute concentration and temperature on the volume changes caused by DMI hydration have been considered. The obvious relationship between the D₂O–H₂O solvent isotope effects on the partial molar volume and enthalpy of solution of DMI has been discovered.     

Free volume characteristics of 2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene copolymers: Effect of composition and molecular weight

2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene (PDD-TFE) copolymer is a good candidate to prepare gas separation membranes with excellent permeability due to its free volume characteristics. However, the influence of PDD-TFE copolymer structure on its free volume characteristics is less studied. In this paper, PDD-TFE copolymers with different compositions and molecular weights were synthesized, and their free volume characteristics were analyzed by positron annihilation lifetime spectroscopy and a molecular dynamics simulation. It indicated that the molar fraction of PDD in copolymers had a significant effect on free volume characteristics, while the molecular weight of copolymers exerted a slight influence on free volume when the molecular weight exceeded a critical region (intrinsic viscosity [η] > 68 ml g⁻¹). PDD-TFE copolymers with greater PDD molar fractions (i.e., 72% and 84%) showed bimodal distributions in positron lifetime and free volume size distributions, while PDD-TFE copolymers with lower PDD molar fractions (i.e., 27% and 35%) exhibited a single peak. The long-lifetime parameter τ₃ was assigned to micro-cavities formed by [-(TFE)_y-PDD-] segments and τ₄ was attributed to micro-cavities formed by [-(PDD)_x-TFE-] segments. The cis and trans transitions of PDD led to a local multilayer spiral structure with a 2.6–4.3 Å layer spacing, which would also increase the free volume of copolymers.     

Phosphorescence properties and kinetics of the lowest triplet state T1 of a series of pyrene derivatives as obtained by ODMR techniques

The experimental results of an ODMR investigation of the radiative and nonradiative properties of the lowest electronically excited triplet state T₁ of a series of pyrene derivatives are presented. The paper gives the highly resolved phosphorescence spectra of 1,2-benzopyrene, naphtho-(2′, 3′ ; 1,2)-pyrene, anthraceno-(2′, 3′; 1, 2)-pyrene, 1,2:6,7-dibenzo-pyrene, 1,2-benzonaphtho-(2′, 3′; 6, 7)-pyrene and 1,2; 4,5-dibenzo-pyrene along with vibrational analyses and — in part — symmetry assignments. The correlation know from the literature between triplet energies and the ZFS-parameter D is discussed in terms of character orders. Three of the molecules exhibit an unusual deactivation behaviour similar to that of 3,4-benzo-pyrene where the out-of-plane level is not the slowest level. Several possibilities to explain this unexpected behaviour are discussed.     

Fractal character of the SAXS correlation volume in poly(ethylene glycol)/silica hybrid wet gels

Small-angle X-ray scattering (SAXS) was employed to study the nanostructural properties of poly(ethylene glycol)(PEG)/silica hybrid wet gels prepared from hydrolysis of tetraethoxysilane (TEOS) in mixtures with PEG/(PEG + TEOS) molar ratio in the nominal range between 0 and 0.8. The SAXS pattern was found to be well fitted by the scattering from a polymeric particle of radius of gyration R _g with an internal structure of primary silica particles described by a polymeric constraint of a mass-fractal of dimension D. R _g increases with the PEG quantity while D first increases from 2.24 for the pure TEOS-derived gel to reach values between 2.46 and 2.40 with the additions of PEG. The correlation volume V _c as determined by SAXS for such a polymeric structure behaves as a volume-fractal and accordingly scales with R _g as V _c ~ R _g ^D . An overall mean value of about 1 nm could be estimated as an upper limit for the radius of the primary silica particle building up the structure of all the wet gels, independent of the PEG addition.     

Density,excess molar volumes and refractive indices of β-pinene with o,m, p-xylene and toluene at 303.15, 308.15 and 313.15 K

Densities (ρ), excess molar volumes (V^E ), refractive indices (n_D ) and deviation in refractive (Δn_D ) indices on mixing for β-pinene with o-xylene, m-xylene, p-xylene and toluene have been determined at T?=?303.15, 308.15 and 313.15?K. The excess molar volume and deviation in refractive index have been fitted to Redlich–Kister polynomials. In addition, deviations in refractive indices were compared with the predictions of several mixing rules. Results obtained have been discussed in terms of intermolecular interactions.     

Structural Peculiarities of Dioxane Media in H/D Isotope Effects of Water Solvation at 288.15K-318.15K

Using the data of precision densimetry measurements for diluted solutions of H₂O and D₂O in 1,4-dioxane (1,4-DX) at 288.15 K-318.15 K we calculated the limiting partial molar volumes of the H/D isotopomers of water in dioxane and the excess molar volumes of the stated systems. The water molecules dispersed in 1,4-DX form complexes H-bonded into associates whose packing coefficient slightly exceeds that of the structural aggregates in liquid H₂O and D₂O. It is concluded that the structure of 1,4-DX is loosened and concomitantly undergoes volume expansion caused by the water microimpurities. The differentiating temperature effect on the volume solvation effects of H₂O and D₂O in 1,4-DX has been found.Original Russian Text Copyright © 2004 by. E. V. Ivanov, E. Yu. Lebedeva, and V. K. Abrosimov__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 852–861, September–October, 2004.     

Thermoanalytical study of cyclization reaction of some thioureates

Thermal initiated conversion of N-aryl-N'-(2-benzylpyridinium)thioureates into 2-arylamino-4H-benzo[d][1,3]thiazines was studied by non-isothermal differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermal analysis (DTA) in the solid-state. The values of molar reaction ethalpies (DH _r) of six derivatives of thioureates and the melting parameters (T _f, DH _f, DS _f) of the obtained products - benzothiazines were determined by the DSC method. This revised version was published online in August 2006 with corrections to the Cover Date.     

Volumetric Properties of Aqueous Binary Mixtures of 1-Butanol,Butanediols, 1,2,4-Butanetriol and Butanetetrol at 298.15 K

Excess molar volumes, V _m ^E, and partial molar volumes, ↕ ₂, have been determined for dilute aqueous solutions of 1-butanol, 1,2-butanediol, 2,3-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol and 1,2,3,4-butanetetrol (erythritol) at 298.15 K, as a function of composition from density measurements. The limiting partial molar volumes, ↕ ₂∞, of alcohols in aqueous solution are evaluated through extrapolation. Interactions of the different solutes with water are discussed in terms of the relationship among polar and non-polar groups on water structure and the effect of the position of hydroxyl groups in the molecule.     

Complexes of Co(II), Ni(II), Cu(II), and Pd(II) with Sulfametrole-Cyclodiphosph(V)azane Derivatives

Novel [1,3-di-[N ₁ -4-methoxy-1,2,5-thiadiazole-3-yl-sulfanilamide(sulfametrole)]-2″4-bis-[1,3-dithiole-2-thione-4,5-dithiolate]-2′,4′-dichl-orocyclodiphosph(V)azane] (III) , was prepared and their coordinating behavior towards the metal ions Co(II), Ni(II), Cu(II), and Pd(II) was studied. The structures of the isolated products are proposed based on elemental analyses, IR, UV, ¹ H, and ³¹ P NMR, ESR, magnetic susceptibility, molar ratio, conductometric titration and electrical conductivity measurements. The prepared complexes showed high to moderate bactericidal activity compared with the ligand.     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

 The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions.     

Zwischenmolekulare Wechselwirkungen von Jod mit 1,2-Bis-pyridyl-ethylenen und -acetylenen

Spectra of trans-1,2-bis-(2-pyridyl)-ethylene (I), cis-1,2-bis-(2-pyridyl)-ethylene (II), trans-1,2-bis-(4-pyridyl)-ethylene (III), cis-1,2-bis-(4-pyridyl)-ethylene (IV), 1,2-bis-(2-pyridyl)-acetylene (V) and 1,2-bis-(4-pyridyl)-acetylene (VI) with low molar amounts of iodine, in dilute solutions in dichloromethane, are studied in the visible spectral region. Wavelengths and molar extinction coefficients for the shifted iodine band in the visible region, equilibrium constants and the wavelength of the isosbestic point for each system are reported. The experimental results are attributed to the formation of complexes between I–VI and iodine in which one pyridyl ring in I–VI is coordinated with one molecule of iodine.     

THE QUENCHING OF TYROSINE AND TRYPTOPHAN FLUORESCENCE BY H2O AND D2O*

Abstract— The quantum yields and lifetimes of the fluorescence of tyrosine and tryptophan were determined in D₂O-H₂O and glycerol-H₂O solvent mixtures of varying composition from 10 vol.% to 100% H₂O at 15°C. Forboth amino acids the ratio of the quantum yields in D₂O and H₂O (i.e., q_D/q_H) was smaller than the ratio of the corresponding lifetimes (_D/_H). For tyrosine the ratio of the quantum yields in glycerol and H₂O (q_G/q_H) was also smaller than the corresponding _G/_H ratio, but for tryptophan q_G/g_HG/_H. The proximity of the q vs. plots for tyrosine in the two solvent mixtures indicates that at 15°C neither D₂O nor glycerol, in the pure state or when diluted with H₂O, quench tyrosine significantly. However, H₂O quenches tyrosine by a dynamic process, which increases both the radiative and the nonradiative rate constant. The quenching action is attributed to a tyrosine-H₂O exciplex, whose formation is independent of bulk viscosity and dielectric constant. Unlike tyrosine, tryptophan is quenched weakly by D₂O by a static process at 15°C (i.e., involving no change in), but H₂O quenches tryptophan much more efficiently by a dynamic process, which involves the nonradiative rate constant, but not the radiative constant. These results are explained on the basis of electrostatic complexation of the ammonium group to the carbon atom adjacent to the ring nitrogen with a lifetime which is longer thanin D₂O but shorter thanin H₂O, with solvent reorientation possibly also being an important factor in the quenching. This explanation is consistent with the fact that concentrated (8 M) urea increases q andof aqueous tryptophan ? 15–20%, while guanidine hydrochloride (6.4 M) has the opposite effect, i.e., it decreases q and t of tryptophan ? 15–20%, and with the fact that neither 8 M urea nor 6.4 M guanidine hydrochloride affects any fluorescence parameter of tyrosine at all.     

Effect of solvent polarizability on dual fluorescence of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene

The properties of the lowest excited states of EE-1-phenyl,4-(1′-pyrenyl)-1,3-butadiene were studied by absorption and emission spectrometry in solvents of different polarity and polarizability. The effect of the latter on the energy and relative position of the two lowest excited singlet states (of B_u and A_g parentage) was investigated. Dual fluorescence was observed in low polarizability solvents at room temperature. The emission from a thermally populated upper state disappears at low temperature and in higher polarizability solvents, such as CS₂, where the lowest excited state acquires an allowed character. The excited molecule relaxes mainly by the radiative pathway. Internal conversion also plays an important role while the triplet population is scarce and photoisomerization is practically negligible. The behaviour is compared with those of related compounds.     

Tetrahydroberberine,a pharmacologically active naturally occurring alkaloid

Tetrahydroberberine (systematic name: 9,10‐dimethoxy‐5,8,13,13a‐tetrahydro‐6H‐benzo[g][1,3]benzodioxolo[5,6‐a]quinolizine), C₂₀H₂₁NO₄, a widely distributed naturally occurring alkaloid, has been crystallized as a racemic mixture about an inversion center. A bent conformation of the molecule is observed, with an angle of 24.72 (5)° between the arene rings at the two ends of the reduced quinolizinium core. The intermolecular hydrogen bonds that play an apparent role in crystal packing are 1,3‐benzodioxole –CH₂...OCH₃ and –OCH₃...OCH₃ interactions between neighboring molecules.     

Apparent Molar Volume and Viscosity Studies on Some Carbohydrates in Solutions

Summary.  The apparent molar volume (φ_v) and viscosity (η) of L(+)-arabinose, D(+)-galactose, D(−)-fructose, D(+)-glucose, sucrose, lactose, and maltose in water and in 0.1% and 0.3% water-Surf Excel solutions were measured as a function of solute concentrations at 308.15, 313.15, and 323.15 K, respectively. The apparent molar volume (φ_v) of the carbohydrates was found to be a linear function of the concentration. From a φ_v versus molality (b) plot, the apparent molar volume at infinite dilution (), which is practically equal to the partial molar volume at infinite dilutions () of these substances was determined. The viscosity coefficients B and D for the carbohydrates were calculated on the basis of the viscosity of the solutions and the solvent using the Jones-Dole equation. The activation free energy for viscous flow (ΔG ^≠) of the solutions was also calculated using the Eyring equation. The carbohydrates showed structure making behaviour both in water and in water-Surf Excel solutions. When water-Surf Excel solutions and pure water solutions containing carbohydrate molecules are compared, the former were found to be more structured. The behaviour of these solutes in water and in water-Surf Excel solution systems is discussed in the light of solute–solvent interactions. Corresponding author. E-mail: chemistry_ru@yahoo.com Received March 19, 2002; accepted (revised) July 31, 2002 Published online February 24, 2003     

Gas transport properties of annealed polyimide films

Sorption and permeation of CO₂ in various annealed polyimide (PI) films were investigated. Dual-mode sorption and partial immobilization models were used to analyze the data. Sorption of CO₂ in PI film quenched from above the glass transition temperature (T_g) is greater than in film as received. In fact, sorption is decreased over the entire pressure range by cooling the film slowly. These changes in sorption of CO₂ can be attributed to a change in the Langmuir sorption capacity C′_H by annealing, since the other dual-mode sorption parameters, k_D and b, are almost independent of annealing. The value of C′_H is increased by quenching, and decreased by slow cooling from above T_g. The two diffusion coefficients D_D and D_H according to the Henry and Langmuir modes, respectively, for CO₂ also depend markedly on annealing. Diffusion coefficients of quenched PI films are increased and those of film cooled slowly are decreased compared with values for PI film as received. The change in D_H is larger than that in D_D. The permeability coefficient of quenched PI films at 100 cmH_g is about 1.7 times that of PI film as received. The film structure formed by quenching can enhance permselectivity.     

Weak C—H...X (X = O,N) hydrogen bonds in the crystal structure of dihydroberberine

Dihydroberberine (systematic name: 9,10‐dimethoxy‐6,8‐dihydro‐5H‐1,3‐dioxolo[4,5‐g]isoquinolino[3,2‐a]isoquinoline), C₂₀H₁₉NO₄, a reduced form of pharmacologically important berberine, crystallizes from ethanol without interstitial solvent. The molecule shows a dihedral angle of 27.94 (5)° between the two arene rings at the ends of the molecule, owing to the partial saturation of the inner quinolizine ring system. Although lacking classical O—H or N—H donors, the packing in the crystalline state is clearly governed by C—H...N and C—H...O hydrogen bonds involving the two acetal‐type C—H bonds of the 1,3‐dioxole ring. Each dihydroberberine molecule is engaged in four hydrogen bonds with neighbouring molecules, twice as donor and twice as acceptor, thus forming a two‐dimensional sheet network that lies parallel to the (100) plane.     

H 2 O-D2O Solvent Isotope Effect on Excess Molar Volumes of 3-Methylpyridine Solutions

Densities of 3-methylpyridine (3-MP) + water and 3-methylpyridine + heavy water were measured in the 3-MP mole fraction range 0.002–0.04 from 298 to 318 K. The excess molar volumes of 3-MP + D₂O mixtures were found to be more negative than those of 3-MP + H₂O mixtures. The partial molar volume of 3-MP at infinite dilution is smaller in D₂O than in H₂O which suggests that 3-MP causes a structure-breaking effect in water which is more pronounced in D₂O. It was found that the volume change with concentration in dilute solutions of 3-MP in water and heavy water can be adequately described by the pair-wise interaction of the solute molecules. The molal volume second-virial coefficient, V _xx , is positive indicating that the water molecules are less structured in the cospheres of the solute pairs than in the bulk solvent. The temperature dependence of V _xx displays a maximum at around 308 K in the case of D₂O solutions, whereas V _xx increases almost linearly with temperature in H₂O solutions.     

Effect of sub-Tg relaxations on chromophore reorientation in corona-poled polymers

Activation volumes for chromophore reorientation were measured for a series of guest–host polymeric materials, indicating a significant coupling between chromophore motion and the glassy α and β relaxation dynamics of the polymer host. The specific systems studied were formed by individually dissolving N,N-dimethyl-p-nitroaniline (DpNA), 4-(dimethylamino)-4′-nitrotolane (DMANT), 4-(diethylamino)-4′-nitrotolane (DEANT), and 1-((4-(dimethylamino)phenyl)ethynyl)-4-((4-nitrophenyl)ethynyl)benzene (DMAPEANT) in poly(methyl methacrylate) (PMMA), poly(ethyl methacrylate) (PEMA), and poly(isobutyl methacrylate) (PiBMA). In each of these systems, the isothermal, sub-T_g decay of the second-order optical susceptibility χ⁽²⁾ was monitored as a function of pressure using second harmonic generation. In each system, the observed decay of χ⁽²⁾ was represented by a stretched exponential equation from which the decay time τ₀ and decay distribution width β_KWW were determined. For each dopant molecule, the decrease in activation volume with the increasing size of the polymer host's alkyl side group and the pressure dependence of β_KWW were indicative of partial coupling between chromophore rotation and the glassy β relaxation dynamics of the polymer host. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1013–1024, 1998