Hydrolysis of 1,4-cyclohexanedimethanol-based copolyester

The solid state hydrolysis of a copolyester based on a mixture of 1,4-cyclohexanedimethanol and ethylene glycol condensed with terephthalic acid was studied at 100°C and 57 to 96 kPa water vapor partial pressure (55% to 95% relative humidity). The equilibrium water sorption in weight percent (C_∞) was found to be where P is the water vapor partial pressure in kPa. For specimens 0.32-cm thick, it took about 24 h to reach 0.9C_∞. The intrinsic viscosity (IV) was measured and used to calculate the relative change in molecular weight (M?_w) from the relationship IV ∝? (M?_w)^0.7. The decrease in molecular weight was linear with time, and the rate of decrease was found to be proportional to C_∞; the empirical correlation is where the rate constant, k, is in day^?1. A decrease of 50% in M?_w was observed after 22 days at 95% relative humidity.     

Grignard-Synthese sauerstofffreier Poly(borocarbosilane)

Grignard-Synthesis of Oxygen-free Poly(borocarbosilanes) A series of modified oxygen-free poly(borocarbosilanes) was synthesized by the reaction of the monomeres dichlorodiphenylsilane, 1,4-dibromobenzene or α, α-dichlorotoluene, dichloro-phenylborane or boron tribromide with magnesium. This simple variation of the Grignard method led to the products [(Ph₂Si)₄(BPh)Ar]_x and [(Ph₂Si)₄BAr]_x with the carbosilane bridge Ar = 1,4-C₆H₄⁻ and CHC₆H₅. The oligomeric poly(borocarbosilances) were analysed and characterized by ¹H, ¹¹B, ¹³C, ²⁹Si NMR and IR spectroscopy. The weight and number averages M_n and M_w were determined by gel-permeation chromatography. The ceramic residues at 1100°C reflect the influence of boron on decreasing the weight loss.     

Application of poly(phthalazinone ether sulfone ketone)s to gas membrane separation

A series of poly(phthalazinone ether sulfone ketone) (PPESK) copolymers containing different component ratios of bis(4‐fluorodiphenyl) ketone and bis(4‐chlorodiphenyl)sulfone with respect to a certain amount of 4‐(4‐hydroxyphenyl)‐2,3‐phthalazin‐1‐one were synthesized by polycondensation. Glass transition temperatures of these polymers were adjusted from 263°C to 305°C by changing the ratios of reactants. Gas permeability and selectivity of the dense membranes of the polymers for three kinds of gases (CO₂, O₂, and N₂) were determined at different temperatures. The result indicated that the membrane of PPESK (S/K = 1/1, mol ratio) had an excellent gas separation property. Permeability of the polymer membranes for CO₂, O₂, and N₂ was P = 4.121 barrier, P = 0.674 barrier, and P = 0.0891 barrier, respectively. Separation factors of α and α were 7.6 and 46, respectively. New material was made into a composite membrane with silicone rubber for blocking up leaks and defects on the surface of its nonsymmetrical membrane. As a result of the test, permeability of the composite membrane was J = 7.2 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg and J = 0.99 × 10⁻⁶ cm³ (STP) cm⁻² S⁻¹ cm⁻¹ Hg, whereas the α was still higher than 7. These showed that PPESKs had a bright prospect as the potential membrane material for high‐temperature gas separation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 2385–2390, 1999     

Molecular weight and molecular weight distribution from dynamic measurements of polymer melts

A method for determining the molecular weight distribution (MWD) of a polymer melt has been developed using the dynamic elastic modulus (G'), plateau modulus (G), and zero shear complex viscosity (η). The cumulative MWD was found to be proportional to a plot of (G'/G)^0.5 vs. measurement frequency (ω). Frequency (ω) was found to be inversely proportional to (MW)^3.4, as expected. Results were scaled to absolute values using the empirical relationship η ∝ (M?_w)^3.4, where M?_w is the weight-average MW. M?_w, M?_n (number-average MW) and M?_w/M?_n calculated from melt measurements were found to agree with size exclusion chromatography usually well within 10 percent for broad and bimodal distribution samples. M?_w/M?_n tended to be approximately 20 percent higher for narrow distribution samples (M?_w/M?_n < 1.2) because we did not account for a finite distribution of relaxation times from a collection of monodisperse polymer chains. We also did not account for the plasticizing effect of short chains mixed with long ones which caused peak positions to be closer together for Theological vs, size exclusive chromatography (SEC) determinations of MW for bimodal distribution blends.     

Kinetic study of the free‐radical polymerization of vinyl acetate in the presence of deuterated chloroform by 1H‐NMR spectroscopy

The free‐radical polymerization of vinyl acetate was performed in the presence of deuterated chloroform (CDCl₃) as a chain‐transfer agent (telogen) and 2,2′‐azobisisobutyronitrile as an initiator. The effects of the initiator and solvent concentrations (or equivalent monomer concentration) and the reaction temperature on the reaction kinetics were studied by real‐time ¹H‐NMR spectroscopy. Data obtained from analysis of the ¹H‐NMR spectra were used to calculate some kinetic parameters, such as the initiator decomposition rate constant (k_d), k_p(f/k_t)^1/2 ratio (where k_p is the average rate constant for propagation, f is the initiator efficiency, and k_t is the average rate constant for termination), and transfer constant to CDCl₃ (C). The results show that k_d and k_p(f/k_t)^1/2 changed significantly with the solvent concentration and reaction temperature, whereas they remained almost constant with the initiator concentration. C changed only with the reaction temperature. Attempts were made to explain the dependence of k_p(f/k_t)^1/2 on the solvent concentration. We concluded from the solvent‐independent C values that the solvent did not have any significant effect on the k_p values. As a result, changes in the k_p(f/k_t)^1/2 values with solvent concentration were attributed to the solvent effect on the f and/or k_t values. Individual values of f and k_t were estimated, and we observed that both the f and k_t values were dependent on the solvent (or equivalent monomer) concentration. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Relationship in polypropylene melt between its linear viscoelasticity and its steady capillary flow properties

It is the object of the present study to obtain clear knowledge of the relations in the polypropylene melt between its linear viscoelasticity and its nonlinear steady capillary flow, paying particular attention to the elastic properties in its capillary flow. By representing the linear viscoelasticity numerically with zero-shear viscosity, η₀, and steady-state compliance, J, evaluation has been made of the properties concerning the elasticity of polymer melt in the capillary flow, such as non-Newtonianity, the entrance pressure loss, the end correction, the Barus effect, and the melt fracture. The steady flow viscosity η, the entrance pressure loss P₀, the critical shear stress, τ_c, and the critical shear rate $\dot \gamma _c$ at which melt fracture begins to occur are subject to η₀ as follows: From the well-known relationship between η and the weight-average molecular weight M?_w, these quantities are governed by M?_w. Meanwhile, for such quantities as structural viscosity index N, end correction coefficient ν, and elastic pressure loss ratio P₀/P, following correlations hold: As η₀ and J are respectively determined mainly by M?_w and the molecular weight distribution MWD, these quantities are governed by both M?_w and MWD. Physical meanings of η₀·J and η₀² · J are, respectively, mean relaxation time and a measure of stored energy in steady flow. The Barus effect has a positive correlation to J, ν, and P₀/P. (The symbol ∝ employed here means positive correlation.)     

Composition and temperature effects on air separation through liquid crystalline alkyl cellulose membranes

The air separation through triheptyl cellulose (THC)/ethyl cellulose (EC) blend membranes containing no more than 20 wt % THC at the temperature range from 298 to 358 K was investigated using a variable volume method. The air-separation ability for the THC/EC membranes were greater than that for the THC-free pure EC membrane. P for the THC/EC membranes was between 1.06–8.89 × 10^?9 cm³ (STP) cm/cm² s cmHg and P/P 3.04–3.66. The THC/EC membrane showed a unique trend in its P/P ? P relationship, i.e., the magnitude of P/P increased simultaneously with that of P. The THC/EC membrane yielded a maximum oxygen concentration in the oxygen-enriched air (OEA) of 39.5% at an OEA flux of 6.99 × 10^?4 cm³ (STP)/s cm² for a pressure difference of 0.43 MPa at 358 K. After 300 h of measurement at 0.40 MPa and 313 K, the efficiency of the concentrating oxygen was almost constant. © 1994 John Wiley & Sons, Inc.     

Conversion of SO2 into elemental sulfur by using the RF plasma technique

This study demonstrates a new approach for converting SO₂ into elemental sulfur by adding CH₄ in a radio-frequency (RF) plasma reactor. With the applied power (P) of the RF reactor specified at 90 W and operating pressure set at 4000 N/m², it was found that as the CH₄/SO₂ ratio (R) was increased from 0.3 to 1.0, most sulfur-containing products were in the form of elemental sulfur. While R was increased from 1 to 2, the content of elemental sulfur was decreased significantly, but CS₂ was increased dramatically. While R was increased from 2 to 3, both elemental sulfur and CS₂ contents became quite comparable. Nevertheless, it was found that both H₂ and CO (that is, syngas) were the main nonsulfur-containing products under all testing conditions. These results indicate that the use of the RF plasma technique was not only beneficial to convert SO₂, but also was able to convert CH₄ into useful materials. For R = 0 (that is, no CH₄ was introduced), it was found that the SO₂ conversion (i.e., η) = 0.084, indicating that the RF plasma process was inadequate to convert pure SO₂ without adding CH₄ as a reducing agent. While R was increased to 2, it was found that η was improved significantly to 0.968 accompanied with η = 0.999. But as R was increased from 2 to 3, both η and η were slightly decreased. Both η and η also were sensitive to the applied power (P). As P was increased from 15 W to 90 W at R = 2, it was found that both η and η were increased dramatically from 0.247 and 0.320 to 0.968 and 0.999, respectively. But as P was increased from 90 W to 120 W, the increase on both η and η became very limited. Based on these, this study suggests that the operating condition of R = 2 and P = 90 W would be the most appropriate combination for SO₂ conversion. © 2004 American Institute of Chemical Engineers AIChE J, 50: 524–529, 2004     

Oxidative coupling of methane over a La2O3/CaO catalyst. Optimization of reaction conditions in a bubbling fluidized-bed reactor

Oxidative coupling of methane over a La₂O₃/CaO catalyst was investigated in laboratory-scale fluidized-bed reactors (ID = 5 and 7 cm) in the following range of reaction conditions: T = 700 – 880°C, P = 41 – 72 kPa and P = 6 – 29 kPa. The maximum C₂₊ selectivity and yield amounted to 73.8% (T = 800°C, X = 13.1%, Y = 9.7%) and 16.0% (T = 840°C, X = 34.0%, S = 47.2%), respectively. Axial gas concentration profiles revealed that C₂₊ selectivity was not only influenced by oxidative consecutive reactions, but also by steam reforming of ethylene. When diluting the catalytic bed (m_cat = 145 g) with quartz (m = 200 and 400 g), a slight decrease of the selectivity (1–2%) was observed. The dilution of the feed gas with nitrogen only led to only a small increase (< 2%) of the C₂₊ selectivity.     

Synthesis and adsorption properties of metal ions of novel azacrown ether crosslinked chitosan

Azacrown ether chitosan (CTSC) was synthesized by the reaction of chitosan with N‐allyl benzo 15‐crown‐5 crown ether. Azacrown ether crosslinked chitosan (CCTSC) was prepared by the crosslinked reaction of CTSC and epichlorodydrin. Their structures were confirmed by infrared spectral analysis and X‐ray diffraction analysis. The adsorption properties of CTSC and CCTSC for metal ions were also investigated. The experimental results showed that the two chitosan derivatives not only had a good capacity to adsorb Pd²⁺ and Ag⁺ but also was highly selective for Pd²⁺ and Ag⁺ in the coexistence system containing other metal ions. At 20°C ± 1°C and pH = 4, the adsorption capacity of CTSC and CCTSC for Pd²⁺ was 186.1 and 173.1 mg/g, respectively; and for Ag⁺ was 90.2 and 56.5 mg/g, respectively. The selectivity coefficients were K = 6.99, K = ∞, K = 35.38, K = ∞ for CTSC and K = 10.66, K = ∞, K = 85.45, K = ∞ for CCTSC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2705–2709, 2006     

Sorption and transport properties of the semi‐interpenetrating network based on crosslinked poly(vinyl alcohol) and poly(styrene sulfonic acid‐co‐maleic anhydride) as proton‐conducting membranes

This study investigates the sorption and transport properties of hydrocarbon membranes based on poly(vinyl alcohol) network and poly(styrene sulfonic acid‐co‐maleic acid) (PSSA‐MA). The water and methanol self‐diffusion coefficients through an 80 wt % PSSA‐MA interpenetrating SIPN‐80 membrane measured 3.75 × 10^?6 and 5.47 × 10^?7 cm²/s, respectively. These results are lower than the corresponding values of Nafion® 115 (8.89 × 10^?6 cm²/s for water and 8.63 × 10^?6 cm²/s for methanol). The methanol permeability of SIPN‐80 membrane is 4.1 × 10^?7 cm²/s, or about one‐fourth that of Nafion® 115. The difference in self‐diffusion behaviors of Nafion® 115 and SIPN‐80 membranes is well correlated with their sorption characteristics. The solvent uptake of Nafion® 115 increased as the methanol concentration increased up to a methanol mole fraction of 0.63, and then decreased. However, the solvent uptake of the SIPN‐80 membranes decreased sluggishly as the methanol concentration increased. The λ values of water and methanol (i.e., λ and λ) in Nafion® 115 are quite close, indicating no sorption preference between water and methanol. In contrast, the λ value is only one‐third λ for a SIPN‐80 membrane. Accordingly, the SIPN membranes are regarded as candidates for direct methanol fuel cell applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Recognition by nonaromatic and stereochemical subunit-containing polyamides of the four Watson-Crick base pairs in the DNA minor groove

In order to develop an optimal subunit as a T‐recognition element in hairpin polyamides, 15 novel chirality‐modified polyamides containing (R)‐α,β‐diaminopropionic acid (^Rβ), (S)‐α,β‐diaminopropionic acid (^Sβ), (1R,3S)‐3‐aminocyclopentanecarboxylic acid (^RSCp), (1S,3R)‐3‐amino‐cyclopentanecarboxylic acid (^RSCp), (1R,3R)‐3‐aminocyclopentanecarboxylic acid (^RRCp) and (1S,3S)‐3‐amino‐cyclopentanecarboxylic acid (^SSCp) residues were synthesized. Their binding characteristics to DNA sequences 5′‐TGC N CAT‐3′/3′‐ACG N′ GTA‐5′ ( N?N′ =A ? T, T ? A, G ? C and C ? G) were systemically studied by surface plasmon resonance (SPR) and molecular simulation (MSim) techniques. SPR showed that polyamide 4 , AcIm‐^Sβ‐ImPy‐γ‐ImPy‐β‐Py‐βDp (β/^Sβ pair), bound to a DNA sequence containing a core binding site of 5′‐TGC A CAT‐3′ with a dissociation equilibrium constant (K_D) of 4.5×10^?8 m. This was a tenfold improvement in specificity over 5′‐TGCTCAT‐3′ (K_D=4.5×10^?7 M ). MSim studies supported the SPR results. More importantly, for the first time, we found that chiral 3‐aminocyclopentanecarboxylic acids in polyamides can be employed as base readers with only a small decrease in binding affinity to DNA. In particular, SPR showed that polyamide 9 (^RRCp/β pair) had a 15‐fold binding preference for 5′‐TGCTCAT‐3′ over 5′‐TGCACAT‐3′. A large difference in standard free energy change for A ? T over T ? A was determined (ΔΔG^o=5.9 kJ mol^?1), as was a twofold decrease in interaction energy by MSim. Moreover, a 1:1 stoichiometry ( 9 to 5′‐TGC T CAT‐3′/3′‐ACG A GTA‐5′) was shown by MSim to be optimal for the chiral five‐membered cycle to fit the minor groove. Collectively, the study suggests that the (S)‐α‐amino‐β‐aminopropionic acid and (1R,3R)‐3‐aminocyclopentanecarboxylic acid can serve as a T‐recognition element, and the stereochemistry and the nature of these subunits significantly influence binding properties in these recognition events. Subunit (1R,3R)‐3‐aminocyclopentanecarboxylic acid broadens our scope to design novel polyamides.     

Catalytic steam pyrolysis of a selected saturated hydrocarbon on calcined mineral particles

At a total pressure of 101.3 kPa, and in the presence of water vapor (P = 32 kPa), the impact of commercially available Norwegian and Swedish quarried mineral rocks on the gaseous product yields and selectivities generated during the catalytic steam pyrolysis of n-heptane (P_n-C7H16, = 2.9-4.7 kPa) in the intermediate temperature range of 973–1073 K and GHSV 1200–4000 h^?1 was investigated. The results indicate that the choice of calcined mineral particles as the bed material influences the product distribution of alkenes. In particular, calcined dolomites [CaMg(O)₂] suppressed the evolution of unsaturated and aromatic hydrocarbon species; however, the formation of ethylene (C₂H₄) was correlated. A Langmuir-Hinshelwood mechanism has also been proposed to describe the rate equation of the vapor-phase steam pyrolysis of n-heptane on calcined dolomite at 973 K.     

Decay of the HO2 and O−2 Radicals Catalyzed by Superoxide Dismutase. A Pulse Radiolytic Investigation

The pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O^?₂ and HO₂, in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 10⁹ M^?1 sec^?1, decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO^?₂ or E^?) from one enzyme (E) molecule and one O^?₂ radical ion; (2) regeneration of E by a reaction of this product with an additional O^?₂ ion radical. The reaction rate constants k = (1.4 ± 0.2) × 10⁹ and k = (1.9 ± 0.6) × 10⁹ M^?1 sec^?1 were measured at pH = 7 in an oxygenated 0.16 M sodium formate solution.     

Oxygen/nitrogen transport in ionomer composite membranes containing a cobalt Schiff base complex

Different amounts of (N,N′‐disalicylideneethylenediamin)cobalt (CoS) were blended to a cobalt (II)‐neutralized sulfonated EPDM (Co^(II)‐S‐EPDM) ionomer membrane to enhance its oxygen‐enriching ability. Various influence factors on permeabilities and selectivities of the composite membranes, such as the gas pressure difference, the CoS content, and the testing temperature have been investigated. Oxygen permeability coefficients (P) and oxygen/nitrogen separation factors (α) increased simultaneously by decreasing the gas pressure difference or by increasing the CoS content. In comparison with the EPDM matrix, P and α of Co^(II)‐S‐EPDM–CoS (85/15) composite membrane increased from 11.0 Barrer and 4.38 to 37.0 Barrer and 9.60. Obvious enhancement in the oxygen‐enriching property shows that the dual actions of cobaltous ion crosslinking and addition of an abundant cobalt complex may be an effective way to improve a rubbery polymer membrane. As high as 15 wt % of the CoS could be blended. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1071–1077, 1999     

Radiolysis of Fremy's Salt in the Presence of Some Hydrated Electron Scavengers in Alkaline Aqueous Solution

Fremy's salt, ON(SO₃)₂^2?, was irradiated with γ-rays in deaerated alkaline aqueous solutions in the presence of NO₃^?, N₂O. In the presence of N₂O an increase of the G(-ON(SO₃)₂^2? = G from 6.1 to about 6.7 was observed within a limited range of concentration, while with NO₃^? the change is gradual. This is consistent with NO₂ and OH produced, respectively, in the reaction of e_aq^? with Fremy's salt, taking place in one-electron-equivalent processes, and with the assumption that pairs of radicals may originate from water molecules.     

Preparation of supported La0.66Sr0.34Ni0.3Co0.7O3 perovskite catalysts and their performance in methane and odorized natural gas combustion

Three industrially applicable forms of supported La_0.66Sr_0.34Ni_0.3Co_0.7O₃ perovskite combustion catalyst were prepared: alumina pellets coated with perovskite powder, perovskite formed in situ on ceramic fibers, and perovskite formed in situ in fluidizable particles. Kinetics of methane combustion over these catalysts was determined in a plug-flow reactor. For the fiber supported catalyst as the representative one, the effects of various operational conditions on the performance were evaluated in a CSTR Berty reactor. The combustion was inhibited by carbon dioxide, but water had no effect. No carbon monoxide was detected in the effluents even when combusting a methane-rich mixture. No measurable effect of combusting commercial natural gas odorized by ～10 mL/m³ methyl mercaptan was observed, although the catalyst was slowly deactivated by 150 mL/m³ mercaptan in the feed. A simple kinetic model which takes CO₂ inhibition into account is proposed: r = k₂ P/(1 + K_inh P).     

Preparation and characterization of positively charged composite nanofiltration membranes by coating poly(ether ether ketone) containing quaternary ammonium groups on polysulfone ultrafiltration membranes

The novel positively charged poly(ether ether ketone)s (PEEKs) with pendant quaternary ammonium groups were synthesized by copolymerization of 3, 3′‐dimethylaminemethylene‐4,4′‐biphenol (DABP), 3,3′,4,4′‐tetramethylbiphenol, and 4,4′‐bisfluorobenzophenone followed by reaction with iodomethane. The resulting copolymers were used to prepare thin film composite (TFC) nanofiltration (NF) membranes via the dip‐coating method. The effects of different parameters such as copolymer concentration and curing time on the membrane performance (flux and rejection of inorganic salts) were investigated. The optimum parameters were that 1.5 wt % quaternary ammonium PEEK containing 1.8 quaternary ammonium groups per unit with 0.5 wt % DMSO coated on the polysulfone (PSf) support membrane and cured at 100°C. The results of the performance testing showed that the trend for rejection was R > R > R_NaCl > R (R = rejection), which was a typical positively charged membrane. The best performance of these composite nanofiltration membranes was 91.3% rejection for 500 ppm MgCl₂ and 62.5 L/m² h water permeability at 0.4 MPa. The MWCO of the membrane was 800 Da. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

K‐Promoted Hydrotalcites for CO2 Capture in Sorption Enhanced Reactions

Potassium‐promoted hydrotalcite‐like material was prepared with potassium nitrate as the K precursor. The highest ever reported CO₂ adsorption capacity (1.13 mol kg^–1) was obtained at 656 K with p = 0.5 bar at humid conditions. A mathematical model was developed and it satisfactorily simulated the adsorption and desorption processes. The stability of the material was tested with repeated adsorption/desorption cycles; the CO₂ adsorption capacity decreased around 7 % after ten cycles. In addition, regeneration was performed with temperature swing operation (from 656 K to 708 K), where a complete regeneration was achieved within 60 min, which reduced to half the time required for regeneration under isothermal conditions.     

Synthesis,characterization, and adsorption properties of chitosan azacrown ethers bearing hydroxyl group

Two new chitosan azacrown ethers bearing hydroxyl groups (CTS‐DH and CTS‐DO) were synthesized by the reaction of 3‐hydroxyl‐1,5‐diaza‐cycloheptane and 3‐hydroxyl‐1,5‐diaza‐cyclooctane with epoxy‐activated chitosan. Their structures were characterized by elemental analysis, infrared spectra analysis, and X‐ray diffraction analysis. The adsorption and selectivity properties of the hydroxyl azacrown ethers chitosan derivatives for Ag⁺, Cr³⁺, Cd²⁺, and Pb²⁺ were also investigated. The experimental results showed that the two novel chitosan azacrown ethers have good adsorption capacity for Ag⁺, and also showed that the grafted chitosan azacrown ethers have high selectivity for the adsorption of Ag⁺ in the presence of Pb²⁺ and Cd²⁺. The selectivity coefficients of CTS‐DH and CTS‐DO were K = 21, K = 42, K = 20.5, K = 41, respectively. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1793–1798, 2001