Diffusion of poly(ethylene glycol) and ectoine in NIPAAm hydrogels with confocal Raman spectroscopy

The diffusion behavior of poly(ethylene glycol) (PEG) in N-isopropylacrylamide (NIPAAm) hydrogels was investigated using confocal Raman spectroscopy with regard to temperature (25°C, 30°C and 35°C), PEG concentration (10 and 40?wt.%), PEG molecular weight (2,000 and 12,000?g/mol) and addition of the compatible solute ectoine (0.1 and 2?wt.%). Swelling and shrinking of the gels was observed by means of confocal Raman spectroscopy. The swelling behavior of NIPAAm gels in aqueous solutions of PEG and ectoine was found to resemble the swelling behavior in pure water with regard to temperature, i.e., the gel shrinks with increasing temperature. However, the presence and concentration of PEG and ectoine influence the swelling behavior by lowering the volume phase-transition temperature of the gel and facilitating shrinking. In some cases, a re-swelling of the gel was observed after the initial shrinking at the onset of PEG diffusion, which can be explained by PEG changing the chemical potential in the gel phase as it diffuses into the sample allowing the water to re-enter. The expulsion of water from the gel during shrinking and the so-caused increase of PNIPAAm and PEG concentrations in some cases led to the PEG diffusion seemingly being faster in more shrunken gels despite of their higher diffusion resistance.     

Ethylbenzene solubility,diffusivity, and permeability in poly(dimethylsiloxane)

The pure‐gas sorption, diffusion, and permeation properties of ethylbenzene in poly(dimethylsiloxane) (PDMS) are reported at 35, 45, and 55 °C and at pressures ranging from 0 to 4.4 cmHg. Additionally, mixed‐gas ethylbenzene/N₂ permeability properties at 35 °C, a total feed pressure of 10 atm, and a permeate pressure of 1 atm are reported. Ethylbenzene solubility increases with increasing penetrant relative pressure and can be described by the Flory–Rehner model with an interaction parameter of 0.24 ± 0.02. At a fixed relative pressure, ethylbenzene solubility decreases with increasing temperature, and the enthalpy of sorption is −41.4 ± 0.3 kJ/mol, which is independent of ethylbenzene concentration and essentially equal to the enthalpy of condensation of pure ethylbenzene. Ethylbenzene diffusion coefficients decrease with increasing concentration at 35 °C. The activation energy of ethylbenzene diffusion in PDMS at infinite dilution is 49 ± 6 kJ/mol. The ethylbenzene activation energies of permeation decrease from near 0 to −34 ± 7 kJ/mol as concentration increases, whereas the activation energy of permeation for pure N₂ is 8 ± 2 kJ/mol. At 35 °C, ethylbenzene and N₂ permeability coefficients determined from pure‐gas permeation experiments are similar to those obtained from mixed‐gas permeation experiments, and ethylbenzene/N₂ selectivity values as high as 800 were observed. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1461–1473, 2000     

Low-temperature thermal decomposition of an epoxy resin

The thermal decomposition of the epoxy resin system, MY720 (70 wt % tetraglycidyl diaminodiphenyl methane), cured with Eporal (diamino diphenyl sulfone), was investigated at 125–215°C. The primary decomposition product was propenal. Several other aldehydes were observed; however, they are formed during cure and are not thermal decomposition products. The apparent activation energy for the production of propenal was 67 kJ/mol (16 kcal/mol). Possible mechanisms for the source of this compound are discussed.     

Copolymerization of ethylene and 1-butene using a Cr—silica catalyst in a slurry reactor

A novel slurry reactor was used to investigate the copolymerization behavior of ethylene and 1-butene in the presence of 1 wt % Cr on Davison silica (Phillips-type) catalyst over the temperature range of 0–50°C, space velocity of about 0.0051 [m³ (STP)]/(g of catalyst) h, and a fixed ethylene to 1-butene feed mole ratio of 95 : 5. The effect of varying the ethylene to 1-butene feed ratios, 100 : 0, 96.5 : 3.5, 95 : 5, 93 : 7, 90 : 10, 80 : 20, and 0 : 100 mol/mol at 50°C was also studied. The addition of 1-butene to ethylene typically increased both copolymerization rates and yields relative to ethylene homopolymerization with the same catalyst, reaching a maximum yield for an ethylene: 1-butene feed ratio of 95 : 5 at 50°C. The incorporation of 1-butene within the copolymer in all cases was less than 5 mol %. The average activation energy for the apparent reaction rate constant, k_a, based on total comonomer mole fraction in the slurry liquid for the ethylene to 1-butene feed mole ratio of 95 : 5 in the temperature range of 50–30°C measured 54.2 kJ/mol. The behavior for temperatures between 30 to 0°C differed with an activation energy of 98.2 kJ/mol; thus, some diffusion limitation likely influences the copolymerization rates at temperatures above 30°C. A kinetics analysis of the experimental data at 50°C for different ethylene to 1-butene feed ratios gave the values of the reactivity ratios, r₁ = 27.3 ± 3.6 and r₂ ≅ 0, for ethylene and 1-butene, respectively. © 1996 John Wiley & Sons, Inc.     

Absorption of toluene in poly(aryl-ether-ether-ketone)

The absorption and swelling of poly(aryl-ether-ether-ketone) (PEEK) in toluene as a function of resin morphology and temperature in the range 35–95°C was investigated. In all cases the weight gain curves exhibit three characteristics: (1) an induction period, which is a strong function of both temperature and initial crystallinity, (2) a main absorption region, which is linear with square-root time, and (3) a final equilibrium value, namely, solubility. The solubility of amorphous PEEK decreases with temperature and the heat of solution is ?0.93 kcal/mol. The induction period varies with the fourth power of the crystallinity and decreases with temperature with an apparent activation energy of 50 kcal/mol. The strength of the interaction between the crystalline regions is markedly reduced at temperatures greater than 80°C. Swelling accompanying the absorption of the toluene is highly anisotropic with most of the dimensional changes occurring in the thickness direction. The deswelling process, however, is essentially isotropic. The concentration of toluene in solution has a strong effect on the transport process; the equilibrium solubility of toluene in amorphous PEEK immersed in a toluene/iso-octane mixture is a linear function of toluene concentration; but the pseudo-diffusion coefficient for the absorption of toluene varies approximately with the fourth power of its concentration.     

Rheological and rheokinetic properties of phosphazene-containing epoxy oligomers

The rheological and rheokinetic properties of a two-component binder consisting of epoxy-diane oligomers and the oligoepoxyphosphazenes PEO-1 (30 wt %) and PEO-2 (40 wt %) are studied. The viscosities of the initial oligomers at 40°C are 130 (PEO-1) and 270 (PEO-2) Pa s; the activation energies of viscous flow in the range 40–70°C are from 122 to 128 kJ/mol. The addition of equivalent amounts of curing agents, such as triethylenetetramine or iso-methyltetrahydrophthalic anhydride, reduces the initial viscosity of a composition, most strongly in the presence of the second curing agent (by a factor of 50–100). The activation energies of the cure process with triethylenetetramine in the range 45–95°C are 89 (PEO-1) and 125 (PEO-2) kJ/mol, and the gelation time at 55°C is 6 min for both oligomers. The time of gelation for the system PEO–iso-methyltetrahydrophthalic anhydride at 90°C is 475 min, and the glass-transition temperatures of the cured compositions are 238 (PEO-1) and 250°C (PEO-2), as evidenced by thermomechanical studies.     

Base-catalyzed tritium exchange between tritium-containing heavy water and deuterated chloroform–kinetics and equilibrium

We develop a kinetic model for the exchange of tritium and deuteriumbetween tritium-containing heavy water and deuterated chloroform in a two-phase liquid system, catalyzed by hydroxide ion (sodium hydroxide). For the exchange reaction yielding tritiated chloroform andheavy water, the measured equilibrium constant is 0.518 at 25–45°C, independent of temperature. The rate constant (for the controlling step, deuteron abstraction from chloroform) is 0.22 L/mol s at 25°C, 0.72 at 35°C, and 2.0 at 45°C, corresponding to an activation energy of 87 kJ/mol. Comparison is made with literature data, and effects of mass transfer on the apparent rate constant are discussed.     

An ONIOM and DFT study of water and ammonia adsorption on anatase TiO2 (001) cluster

Density functional theory (DFT) calculations at ONIOM DFT B3LYP/ 6‐31G**‐MD/UFF level are employed to study molecular and dissociative water and ammonia adsorption on anatase TiO₂ (001) surface represented by partially relaxed Ti₂₀O₃₅ ONIOM cluster. DFT calculations indicate that water molecule is dissociated on anatase TiO₂ (001) surface by a nonactivated process with an exothermic relative energy difference of 58.12 kcal/mol. Dissociation of ammonia molecule on the same surface is energetically more favorable than molecular adsorption of ammonia (?37.17 kcal/mol vs. ?23.28 kcal/mol). The vibration frequency values also are computed for the optimized geometries of adsorbed water and ammonia molecules on anatase TiO₂ (001) surface. The computed adsorption energy and vibration frequency values are comparable with the values reported in the literature. Finally, several thermodynamical properties (ΔH°, ΔS°, and ΔG°) are calculated for temperatures corresponding to the experimental studies. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Sorption,diffusion, and permeation of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne)

The solubility, diffusivity, and permeability of ethylbenzene in poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) at 35, 45 and 55 °C were determined using kinetic gravimetric sorption and pure gas permeation methods. Ethylbenzene solubility in PTMSP was well described by the generalized dual‐mode model with χ = 0.39 ± 0.02, b = 15 ± 1, and C^′_H = 45 ± 4 cm³ (STP)/cm³ PTMSP at 35 °C. Ethylbenzene solubility increased with decreasing temperature; the enthalpy of sorption at infinite dilution was −40 ± 7 kJ/mol and was essentially equal to the enthalpy change upon condensation of pure ethylbenzene. The diffusion coefficient of ethylbenzene in PTMSP decreased with increasing concentration and decreasing temperature. Activation energies of diffusion were very low at infinite dilution and increased with increasing concentration to a maximum value of 50 ± 10 kJ/mol at the highest concentration explored. PTMSP permeability to ethylbenzene decreased with increasing concentration. The permeability estimated from solubility and diffusivity data obtained by kinetic gravimetric sorption was in good agreement with permeability determined from direct permeation experiments. Permeability after exposure to a high ethylbenzene partial pressure was significantly higher than that observed before the sample was exposed to a higher partial pressure of ethylbenzene. Nitrogen permeability coefficients were also determined from pure gas experiments. Nitrogen and ethylbenzene permeability coefficients increased with decreasing temperature, and infinite dilution activation energies of permeation for N₂ and ethylbenzene were −5.5 ± 0.5 kJ/mol and −74 ± 11 kJ/mol, respectively. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1078–1089, 2000     

Sorption and addition of bromine from aqueous solutions on cis-1,4-polyisoprene

The sorption of bromine from bromine water on cis-1,4-polyisoprene film and the initial stages of bromination are studied at concentrations of 0.002–0.1 mol/l and temperatures of 15–35°C. The diffusion coefficient of bromine into natural rubber (NR) is 1.3–2.0 × 10^?6 cm²/sec for the total sorption and 5–13 × 10^?7 cm²/sec for the irreversible sorption. The partition coefficient of bromine between water and rubber increased from 17.3 at 15°C to 37.1 l/kg at 35°C. The chemical potential, enthalpy and change in entropy of partition are, at 25°C, respectively: ?1.9 kcal/mol, 6.6 kcal/mol and 28.4 cal/mol. K. The irreversible sorption is due to a charge-transfer complex between bromine molecules and double bonds of the rubber. The complex is the first stage of the addition reaction, which becomes noticeable at concentrations above 0.012 mol/l. With increasing bromine concentration the concentration of the complex decreases and the added bromine increases. The charge transfer complex appears to change the conformation of the cis-NR chains so that the bromine addition occurs in the trans-conformation, as shown by FT–IR spectra. The bromination is accompanied by a marked crystallization effect as illustrated by thermal analysis and WAXS measurements.     

Electrokinetic parameters of ion transport across isolated pepper cuticular membranes

The transport of NaCl and CaCl₂ solutions across isolated pepper cuticular membranes was studied by means of conductivity, membrane potential and diffusion experiments. Some characteristic membrane parameters such as the electrical resistance, ionic and salt permeabilities were obtained as a function of the electrolyte concentrations. Cuticle morphological asymmetry accounts for differences in membrane potential values under external reverse gradients. The influence of temperature on the membrane structure was also considered, but only small changes in the electrokinetic parameters were obtained. From the NaCl diffusion experiments two activation energies were determined (54.8 kJ/mol for temperature ranging between 15 and 35°C, and 20.6 kJ/mol for the interval of temperature between 40 and 60°C), which could be associated to thermal transitions in the molecular structure of the cuticle for the interval 30–40°C.     

Oxygen Diffusion into Polymer-Clay Composite Films as a Function of Clay Content and Temperature

Summary: A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene-clay composite films as a function of clay content and temperature. The composite films were prepared from a mixture of surfactant-free pyrene-labeled polystyrene latexes and modified Na-montmorillonite clay of various compositions at room temperature. Diffusion measurements were performed with films at room temperature for seven different clay contents (0, 5, 10, 20, 30, 50 and 60 wt.%). The diffusion coefficients of oxygen increased from 7.4 × 10⁻¹⁰ to 26.9 × 10⁻¹⁰ cm²s⁻¹ with increasing clay content. On the other hand, diffusion measurements were performed over a temperature range of 25–70 °C for 0, 5 and 20 wt.% clay content films. The calculated diffusion activation energies decreased from 2.44 to 0.44 kcal/mol with increasing clay content. No clay content and temperature effects were observed on quenching rate constant and mutual diffusion coefficient values. The results showed that the diffusion coefficients are strongly dependent on both the temperature and clay content in the film.     

Thermal degradation study of isotactic polypropylene using factor-jump thermogravimetry

The degradation of isotactic polypropylene in the range 390–465°C was studied using factor-jump thermogravimetry. The degradations were carried out in vacuum and at pressures of 5 and 800 mm Hg of N₂, flowing at 100–400 standard mL/s. At 800 mm Hg this corresponds to linear rates of 1–4 mm/s. In vacuum bubbling in the sample caused problems in measuring the rate of weight loss. The apparent activation energy was estimated as 61.5 ± 0.8 kcal/mol (257 ± 3 kJ/mol). In slowly flowing N₂ at 800 mm Hg pressure the activation energy was 55.1 ± 0.2 kcal/mol (230 ± 0.8 kJ/mol) for isotactic polypropylene and 51.1 ± 0.5 kcal/mol (214 ± 2 kJ/mol) for a naturally aged sample of atactic polypropylene. For isotactic polypropylene degrading at an external N₂ pressure of 5 mm Hg the apparent activation energy was 55.9 ± 0.3 kcal/mol (234 ± 1 kJ/mol). A simplified degradation mechanism was used with estimates of the activation energies of initiation and termination to give an estimate of 29.6 kcal/mol for the ß-scission of tertiary radicals on the polypropylene backbone. Initiation was considered to be backbone scission ß to allyl groups formed in the termination reaction. For initiation by random scission of the polymer backbone, as in the early stages of thermal degradation, an overall activation energy of 72 kcal/mol is proposed. The difference between vacuum and in-N₂ activation energies is ascribed to the latent heat contributions of molecules which do not evaporate as soon as they are formed. At these imposed rates of weight loss the average molecular weights of the volatiles in vacuum and in 8 and 800 mm H_g N₂ are in the ratios 1–1/2–1/9.     

Kinetics of high-temperature oxidation of poly(diphenylphenylene oxide)

Oxidation of poly(2,6-diphenylphenylene oxide) has been studied within the temperature range 380–470°C. The process is autoaccelerated, the maximum rate of oxygen consumption is directly proportional to its pressure. Activation energy changes from 48 kJ/mol below 410° to 110 kJ/mol above 420°. The oxidation rate below 410° depends on the molecular mass of the polymer.     

Thermoanalytical investigation of the synthesis of pyrazine and bipyrazine via the pyrolysis of the bis(pyrazinecarboxylate)copper(II) complex

The pyrolysis of hydrated bis(pyrazinecarboxylate)copper(II) under an argon atmosphere proceeds via the loss of the water molecules at 84–95°C, ΔH=40.4 kJ (mol H₂O)^?1 followed by the thermal decomposition of the complex at 284–325°C, ΔH=97.0 kJ·mol^?1, yielding 0.72 mole of pyrazine, 0.28 mole of bipyrazine, and 2 mole of CO₂ per mole of complex.     

Thermally induced polymerization of isobutylene in the presence of SnCl4: Kinetic study of the polymerization and NMR structural investigation of low molecular weight products

The polymerization reactivity of isobutylene/SnCl₄ mixtures in the absence of polar solvent, was investigated in a temperature interval from −78 to 60 °C. The mixture is nonreactive below −20 °C but slow polymerization proceeds from −20 to 20 °C with the initial rate r₀ of the order 10⁻⁵ mol · l⁻¹ · s⁻¹. The rate of the process increases with increasing temperature up to ∼10⁻² mol · l⁻¹ · s⁻¹ at 60 °C. Logarithmic plots of r₀ and M̄_n versus 1/T exhibit a break in the range from 20 to 35 °C. Activation energy is positive with values E = 21.7 ± 4.2 kJ/mol in the temperature interval from −20 to 35 °C and E = 159.5 ± 4.2 kJ/mol in the interval from 35 to 60 °C. The values of activation enthalpy difference of molecular weights in these temperature intervals are ΔH_Mn = −12.7 ± 4.2 kJ/mol and −38.3 ± 4.2 kJ/mol, respectively. The polymerization proceeds quantitatively, the molecular weights of products are relatively high, M̄_n = 1500–2500 at 35 °C and about 600 at 60 °C. It is assumed that initiation proceeds via [isobutylene · SnCl₄] charge transfer complex which is thermally excited and gives isobutylene radical‐cations. Oxygen inhibits the polymerization from −20 to 20 °C. Possible role of traces of water at temperatures above 20 °C is discussed. It was verified by NMR analysis that only low molecular weight polyisobutylenes are formed with high contents of exo‐ terminal unsaturated structures. In addition to standard unsaturated groups, new structures were detected in the products. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1568–1579, 2000     

A differential scanning calorimeter study of the crystal forms and polymerization kinetics of 2,4-hexadiynyl-1,6-bis(p-toluenesulfonate)

The thermal properties of 2,4-hexadiynyl-1,6-bis(p-toluenesulfonate) have been explored by program temperature and isothermal differential calorimetry. The heat of fusion for the rapidly heated pure solid was 8254 cal/mole (34,540 J/mole) at 367.1°K (93.8°C). This amounts to an entropy change of 22.5 cal/mole °K (94.1 J/mole °K). The energy of activation for the thermal polymerizations was 18.97 kcal/mole (79.37 kJ/mole). The thermal polymerization appears to follow a solid–solid phase transition which proceeds by random homogeneous nucleation throughout the process. The kinetics were simple first order over 70% of the reaction. Programmed temperature studies indicate that during the first 10% of the polymerization a new high temperature (mp 375.4°K) solid phase is formed which acts as the monomer form during the bulk of the reaction.     

Kinetics of Cu<Superscript>2+</Superscript> binding to the poly(acrylic acid) hydrogel

Isothermal kinetics of copper (ion) binding to poly(acrylic acid) (PAA) hydrogel at 20, 25, 35 and 45°C was investigated. Isothermal conversions and kinetic curves of Cu²⁺ binding to the PAA hydrogel were determined. It was found that the well-known kinetic models of Peppas cannot be applied to describing the entire process of Cu²⁺ binding. The new method for the determination of the kinetic model of the Cu²⁺ binding process, as well as the activation energy density distribution functions of PAA hydrogel interaction with Cu²⁺, were established. It was found that Cu²⁺ diffusion to the active centers (with E _a = 9 kJ/mol) has a dominant influence on the kinetics of the process at temperatures T ≥ 30°C, but at T ≥ 30°C and for the degree of bound Cu²⁺ α ≥ 0.2, the interaction of Cu²⁺ from the adsorption center with E _a = 26 kJ/mol is dominant. The text was submitted by the authors in English.     

Thermally degrading polyethylene studied by means of factor-jump thermogravimetry

Degradation of polyethylene in both linear (NBS 1475) and branched (NBS 1476) form has been studied in the range 410–475°C using factor-jump thermogravimetry. In vacuum, the rate of weight loss was erratic because of bubbling in the sample. The apparent overall activation energy was determined to be 65.4 ± 0.5 kcal/mol (273 ± 2 kJ/mol). There was no distinguishable difference between linear and branched samples. In slowly flowing N₂ at 8 mmHg (1 mmHg = 133 Pa), the overall activation energy was determined to be 64.8 ± 0.3 kcal/mol (271 ± 1 kJ/mol) for linear PE and 64.4 ± 0.2 kcal/mol (269 ± 1 kJ/mol) for a sample of PE with one percent branches. In N₂ at 800 mmHg, the values were 62.6 ± 0.5 kcal/mol for linear PE and 61.2 ± 0.6 kcal/mol for the branched sample, the rate of weight loss being smooth in both cases. Changing the linear flow velocities over the range 1–4 mm/sec at 800 mmHg did not affect the results. From the insertion of typical values in the equation relating the overall activation energy for weight loss from linear polyethylene to the activation energies of the component steps, a degradation mechanism involving scission β to allyl groups, with rapid hydrogen abstraction, slower subsequent β scission, and bimolecular termination, is indicated. The activation energy of β scission for secondary alkyl radicals is estimated to be 33 kcal/mol. The reason for the lower activation energies in N₂ is related to the effects of preformed molecules. The average molecular weights of the volatiles in vacuum and for 8 and 800 mmHg N₂ have been shown to be in the ratios 1 to 1/4 to 1/10, respectively, at these imposed rates of weight loss. The activation energies to use for the initial stage of degradation are 70.6 kcal/mol (295 kJ/mol) in vacuum and 67.8 kcal/mol (284 kJ/mol) at atmospheric pressure.     

Reactivity comparison of five‐ and six‐membered cyclic carbonates with amines: Basic evaluation for synthesis of poly(hydroxyurethane)

The reaction of six‐ and five‐membered cyclic carbonates, 5‐(2‐propenyl)‐1,3‐dioxan‐2‐one ( 1 ) and 4‐(3‐butenyl)‐1,3‐dioxolan‐2‐one ( 2 ) with hexylamine and benzylamine was carried out in N,N‐dimethylacetamide at 30, 50, and 70 °C. The six‐membered cyclic carbonate 1 proceeded quantitatively with hexylamine at 30 °C for 24 h, while the five‐membered cyclic carbonate 2 converted in 34%. The reaction rate constants at 50 °C are evaluated as follows; 1.42 L/mol · h ( 1 with hexylamine) > 0.29 L/mol · h ( 1 with benzylamine) > 0.04 L/mol · h ( 2 with hexylamine) > 0.01 L/mol · h ( 2 with benzylamine). The activation energies in the reactions of 1 and 2 with hexylamine were estimated to be 10.1 and 24.6 kJ/mol, respectively. The ring‐strain energy was calculated by the semi‐empirical method using the PM3 Hamiltonian. The ring‐strain energy of the six‐membered cyclic carbonate was 2.86 kcal/mol larger than that of five‐membered one. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 162–168, 2001