Controlled release of aminophylline from poly (N‐isopropylacrylamide‐co‐itaconic acid) hydrogels

N‐Isopropylacrylamide (NIPA) has been copolymerized with itaconic acid (IA) in the presence of N,N‐methylenebisacrylamide (BIS) as crosslinker. The swelling capacity and the release rate of aminophylline at 37 °C are reported. Maximum equilibrium swelling increases as the itaconic acid content in the hydrogel increases. The experimental data suggest clearly that the swelling process obeys second‐order kinetics. According to this, the kinetic constant, k, and the maximum equilibrium swelling, W_∞, have been calculated. Drug release from fully swollen hydrogels follows Fick's law closely, but deviates from it for xerogels. © 2001 Society of Chemical Industry     

Preparation and swelling properties of solution crosslinked poly(cis‐1,4‐butadiene) gels

Poly(cis‐1,4‐butadiene) (PCB) gels were prepared by the crosslinking polymerization of 4‐tert‐butylstyrene (tBS) and divinylbenzene (DVB) onto unvulcanized butadiene rubber with a solution polymerization technique with benzoyl peroxide (BPO) as an initiator. The effects of the reaction conditions, such as the amount of the solvent, the amount of DVB and tBS, and the initiator (BPO), on the equilibrium swelling ratio (Q_e) were also investigated. The highest oil absorbencies of crosslinked gels in xylene and cyclohexane were 51.35 and 32.98 g/g, respectively. A swelling kinetic equation was proposed for this system: Q_t = Q_e ? {Kt + [1/(Q_e ? Q₀)]}^?1, where Q_t is the swelling ratio at time t, Q₀ is the initial swelling ratio, and K is the swelling kinetic constant. This equation fit the experimental results quite well. The diffusion of organic solvents in PCB gels was Fickian. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2241–2245, 2003     

Zur physikalisch‐chemischen Charakterisierung von 5‐Amino‐1‐aryl‐1H‐tetrazolen: Kinetik der Verteilung im Zweiphasensystem Octan‐1‐ol/Wasser

The kinetics of distribution of 27 5‐amino‐1‐aryl‐1H‐tetrazoles in the two‐phase system octan‐1‐ol/water were investigated UV/Vis‐spectrophotometrically at various temperatures. Studies on relationships between the obtained firstorder rate constants (logk₁, logk₂) and the hydrophobicity of the tetrazoles described by their partition coefficients (logP) show a nearly constant rate of transport from the aqueous to the organic phase (k₁) above logP = 1,5 while the reverse rate (k₂) strongly depends on hydrophobicity. In the whole logP range investigated the kinetic behaviour can be described by bilinear relationships between logk and logP corresponding to known kinetic models for distribution processes in two‐layer systems.     

Swelling kinetics of poly(acrylamide)/poly(mono-n-alkyl itaconates) hydrogels

Hydrogels of mono-n-alkyl itaconate/N-acrylamide have been synthesised. The swelling process at three different pH values (acid, neutral and basic) has been studied. The experimental data indicate that our hydrogels follow second-order swelling kinetics. According to this, the kinetic constant, K_∞, and the swelling capacity at equilibrium, W_∞, have been calculated. The influence of the solvent pH and the molar mass of the mono-n-alkyl itaconate monomeric unit has been analysed. It seems that the general balance between the hydrogen bonding and the hydrophobic interactions regulates the swelling process of these hydrogels.     

Kinetics of thermal degradation of thermotropic poly(p‐oxybenzoate‐co‐ethylene‐2,6‐naphthalate) by single heating rate methods

The kinetics of thermal degradation of thermotropic liquid crystalline poly(p‐oxybenzoate‐co‐ethylene‐2,6‐naphthalate) (PHB/PEN) with the monomer ratio of 60 : 40 and PEN in nitrogen was studied by dynamic thermogravimetry (TG). The kinetic parameters, including the activation energy E_a, the reaction order n, and the frequency factor ln(Z) of the degradation reaction for PHB/PEN (60 : 40) and PEN were analyzed by the single heating rate methods of Friedman and Chang. The effects of the heating rate and the calculating method on the thermostable and degradation kinetic parameters are systematically discussed. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3915–3920, 2004     

Delivery of bupivacaine included in poly(acrylamide‐co‐monomethyl itaconate) hydrogels as a function of the pH swelling medium

Copolymeric hydrogels of poly(acrylamide‐co‐monomethyl itaconate) (A/MMI) crosslinked with N,N′‐methylenbisacrylamide (NBA) were synthesized as devices for the controlled release of bupivacaine (Bp). Two compositions of the copolymer, 60A/40MMI and 75A/25MMI, were studied. A local anesthetic was included in the feed mixture of polymerization (2–8 mg Bp/tablet) and by immersion of the copolymeric tablets in an aqueous solution of the drug. A very large amount of Bp (36–38 mg Bp/tablet) was included in the gels by sorption due to interactions between the drug and the side groups of the hydrogels. Swelling and drug release were in accordance with the second Fick's law at the first stages of the processes. The swelling behavior of these copolymers depended on the pH of the medium. The equilibrium swelling degree (W_∞) was larger at pH 7.5 (W_∞ ≈ 90 wt %) than at pH 1.5 (W_∞ ≈ 52–64 wt %) due to the ionization of the side groups of the copolymer. Release of the drug also depended on the pH of the swelling medium; at pH 7.5, about 60% of the included drug was released, and at pH 1.5, about 80% was released. Bp release was controlled by the comonomer composition of the gels, their drug‐load, and the pH of the swelling medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 327–334, 2002     

Release of vitamin B12 from poly(N‐vinyl‐2‐pyrrolidone)‐crosslinked polyacrylamide hydrogels: A kinetic study

Hydrogels, composed of poly(N‐vinyl‐2‐pyrrolidone) and crosslinked polyacrylamide, were synthesized and the release of vitamin B₁₂ from these hydrogels was studied as a function of the degree of crosslinking and pH of the external swelling media. The three drug‐loaded hydrogel samples synthesized with different crosslinking ratios of 0.3, 0.7, and 1.2 (in mol %) follow different drug‐release mechanisms, that is, chain relaxation with zero‐order, non‐Fickian and Fickian, or diffusion‐controlled mechanisms. To establish a correlation between their swelling behavior and drug‐release mechanism, the former was studied by the weight‐gain method and, at the same time, the concentration of the drug released was studied colorimetrically. Various swelling parameters such as the swelling exponent n, gel‐characteristic constant k, penetration velocity v, and diffusion coefficient D were evaluated to reflect the quantitative aspect of the swelling behavior of these hydrogels. Finally, the drug‐release behavior of the hydrogels was explained by proposing the swelling‐dependent mechanism. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1706–1714, 2000     

Untersuchung der CO2‐Absorptionskinetik in wässrigen Lösungen von N,N‐Diethylethanolanmin und N‐Ethylethanolamin

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA and the liquid‐side mass transfer coefficient were determined from the absorption rate measurements in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor was applied for the absorption studies, whereas a zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics.     

Swelling mechanism of porous P(VP‐co‐MAA)/PNIPAM semi‐IPN hydrogels with various pore sizes prepared by a freeze treatment

BACKGROUND: The objective of the work reported was to investigate the effect of gel microstructure on the swelling mechanism. A series of porous gels with various pore sizes were prepared by freeze‐treating a conventional hydrogel that contained various amounts of water at ? 20 °C. Scanning electron microscopy and differential scanning calorimetry were used to characterize the microstructure of the porous gels. RESULTS: The experimental results showed that the water content during freezing was the key factor controlling the microstructure. Measurement of swelling kinetics showed that a greater amount of water during the freezing process would lead to a rapid swelling rate. The apparent diffusion coefficients (D_p) at all times during the swelling process were obtained by fitting the experimental data to the diffusion equation. The values of D_p suggested that the swelling mechanism of the gels depends on the pore size. The diffusion exponent (n) obtained by fitting the fractional mass change (M_t/M_∞) to equation of Fick's law further confirmed that the swelling mechanism of the gels is determined by the pore size. CONCLUSION: The swelling mechanism of the gels is determined by the microstructure related to the pore size and the thickness of struts. The microstructure can be controlled by adjusting the water content of the hydrogels by changing the pH of the swelling medium prior to freezing. Copyright © 2008 Society of Chemical Industry     

High oil‐absorptive composites based on 4‐tert‐butylstyrene‐EPDM‐divinylbenzene graft polymer

4‐tert‐Butylstyrene‐EPDM‐divinylbenzene graft polymer (PBED) was prepared by graft crosslinking polymerization in toluene using BPO as an initiator. Gel and sol of PBED were isolated by extraction with tetrahydrofuran (THF). Sol PBED can be reused as oil absorbent through cross‐linking by ultraviolet irradiation. After swelling in oil, crosslinked polymers have poor gel strength to be taken out of oil wholly at high absorbency, although they possess strong mechanical strength in their dry states. As known, composite technique is one of the useful methods for material reinforcement. Fibres, sponges and non‐woven fabrics were used as reinforcers or supporters in this work. Oil absorbency was measured by method ASTM (F726‐81) and swelling kinetics of the composite was evaluated by an experimental equation. The gel strength parameter S, the relaxation exponent n, and the fractal dimension d_f of polymer and some composites in pseudo‐critical gel state were determined from oscillatory shear measurements by a dynamic rheometer. Mechanical properties and the morphologies of some composites were measured with a tensile tester and scanning electron microscopy, respectively. © 2001 Society of Chemical Industry     

Modified carrageenan. 4. Synthesis and swelling behavior of crosslinked κC‐g‐AMPS superabsorbent hydrogel with antisalt and pH‐responsiveness properties

To synthesize a novel biopolymer‐based superabsorbent hydrogel, 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) was grafted onto kappa‐carrageenan (κC) backbones. The graft copolymerization reaction was carried out in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator, N,N,N′,N′‐tetramethyl ethylenediamine (TMEDA) as an accelerator, and N,N′‐methylene bisacrylamide (MBA) as a crosslinker. A proposed mechanism for κC‐g‐AMPS formation was suggested and the hydrogel structure was confirmed using FTIR spectroscopy. The affecting variables on swelling capacity, i.e., the initiator, the crosslinker, and the monomer concentration, as well as reaction temperature, were systematically optimized. The swelling measurements of the hydrogels were conducted in aqueous solutions of LiCl, NaCl, KCl, MgCl₂, CaCl₂, SrCl₂, BaCl₂, and AlCl₃. Due to the high swelling capacity in salt solutions, the hydrogels may be referred to as antisalt superabsorbents. The swelling of superabsorbing hydrogels was measured in solutions with pH ranging 1 to 13. The κC‐g‐AMPS hydrogel exhibited a pH‐responsiveness character so that a swelling–deswelling pulsatile behavior was recorded at pH 2 and 8. The overall activation energy for the graft copolymerization reaction was found to be 14.6 kJ/mol. The swelling kinetics of the hydrogels was preliminarily investigated as well. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 255–263, 2005     

The effects of the pH value of the swelling medium on the kinetics of the swelling of a poly(acrylic acid) hydrogel

The isothermal kinetics curves of the swelling of a poly(acrylic acid) hydrogel in buffer solutions of different pH values (5, 7, and 9) at temperatures ranging from 30 to 40°C were determined. The possibilities of applying the Fick kinetics model and the Peppas equation were examined. It was found that the applicability of these models were limited. The kinetics model of a first‐order chemical reaction was found to describe the swelling kinetics of the PAA hydrogel in all the investigated buffer solution at all the investigated temperatures. Swelling kinetics is determined by the rate of expansion of the network. The kinetic parameters (E_a, ln A) of the swelling of the PAA hydrogel in buffer solutions of different pH values were determined. The activation energy and the pre‐exponential factor of the swelling of the PAA hydrogel in buffer medium decreased with increasing pH value of the swelling medium. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A Study on CO2 Absorption Kinetics by Aqueous Solutions of N,N‐Diethylethanolamine and N‐Ethylethanolamine

N‐Ethylethanolamine (EEA) and N,N‐diethylethanolamine (DEEA) represent promising candidate alkanolamines for CO₂ removal from gaseous streams, as they can be prepared from renewable resources. In this work, the reaction rate constant for the reaction between CO₂ and EEA was determined from the absorption rate measurements of CO₂ in a blend comprising DEEA, EEA and H₂O. A stirred‐cell reactor with a plane, horizontal gas‐liquid interface was used for the absorption studies. While the DEEA concentration in the formulated solution was varied in the range of 1.5–2.5 kmol/m³, the initial EEA concentration was 0.1 kmol/m³. A zwitterion mechanism for EEA and a base‐catalyzed hydration mechanism for DEEA were used to describe the reaction kinetics. At 303 K, the second‐order reaction rate constant for the CO₂ reaction with EEA was found to be 8041 m³/(kmol s). The liquid‐side mass transfer coefficient was also estimated, and its value (0.004 cm/s) is in line with those typical of stirred‐cell reactors.     

Fast swelling behaviors of thermosensitive poly(N‐isopropylacrylamide‐co‐methacryloxyethyltrimethyl ammonium chloride)/Na2WO4 cationic composite hydrogels

A facile method was explored to synthesize thermosensitive poly[N‐isopropylacrylamide (NIPAM)‐co‐methacryloxyethyltrimethyl ammonium chloride (DMC)]/Na₂WO₄ cationic hydrogels via copolymerization of NIPAM and DMC in the presence of Na₂WO₄. Na₂WO₄ acted as both a physical crosslinking agent and a porogen precursor. The hydrogels were characterized by Fourier transform infrared spectroscopy, energy dispersive X‐ray, thermogravimetry, environmental scanning electron microscopy, and transmission electron microscopy. Effects of various salt solutions, pH solutions on swelling were investigated. Thermosensitivity of the hydrogels were also investigated in various polar solvents at different temperatures. The resultant hydrogel showed a fast swelling rate and good salt tolerance. The hydrogels reached the swelling equilibrium within 10 min. Moreover, the swelling ratio of the hydrogels increased with the increase of the polarity of the solvent. In the water, the swelling ratio decreased with the increasing of temperature, but remained at a high level even at 80 °C since the pore structure weaken the lower critical solution temperature effect of PNIPAM. The swelling ratio increased instead in low polar solvent, while it became negligible in nonpolar solvent with the increasing of temperature. The whole swelling kinetics was fit for Schott's pseudo‐second order model. The hydrogels have a great potential as catalysts and smart materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46375.     

Non‐Isothermal Kinetic Study of the Thermal Decomposition of Melamine 3‐Nitro‐1,2,4‐triazol‐5‐one Salt

Study on thermal behavior of 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) salts was required to obtain important data for application purposes. These compounds have been shown to be useful intermediates for gun propellant ingredients, high energetic ballistic modifiers for solid propellants and other potential applications. In this paper, thermal decomposition and non‐isothermal kinetics of melamine 3‐nitro‐1,2,4‐triazol‐5‐one salt (MNTO) were studied under non‐isothermal conditions by DSC and TG methods. The kinetic parameters were obtained from analysis of the DSC and TG curves by Kissinger and Ozawa methods. The critical temperature of thermal explosion (T_b) was 574 K. The results show that MNTO is thermally more stable than NTO when compared in terms of the critical temperature of thermal explosion. Finally, the values of ΔS^#, ΔH^#, and ΔG^# of its decomposition reaction were calculated.     

Crystallization kinetics of poly(1,4‐butylene‐co‐ethylene terephthalate)

The crystallization kinetics of poly(butylene terephthalate) (PBT), poly(ethylene terephthalate) (PET), and their copolymers poly(1,4‐butylene‐co‐ethylene terephthalate) (PBET) containing 70/30, 65/35 and 60/40 molar ratios of 1,4‐butanediol/ethylene glycol were investigated using differential scanning calorimetry (DSC) at crystallization temperatures (T_c) which were 35–90 °C below equilibrium melting temperature . Although these copolymers contain both monomers in high proportion, DSC data revealed for copolymer crystallization behaviour. The reason for such copolymers being able to crystallize could be due to the similar chemical structures of 1,4‐butanediol and ethylene glycol. DSC results for isothermal crystallization revealed that random copolymers had a lower degree of crystallinity and lower crystallite growth rate than those of homopolymers. DSC heating scans, after completion of isothermal crystallization, showed triple melting endotherms for all these polyesters, similar to those of other polymers as reported in the literature. The crystallization isotherms followed the Avrami equation with an exponent n of 2–2.5 for PET and 2.5–3.0 for PBT and PBETs. Analyses of the Lauritzen–Hoffman equation for DSC isothermal crystallization data revealed that PBT and PET had higher growth rate constant G_o, and nucleation constant K_g than those of PBET copolymers. © 2001 Society of Chemical Industry     

Structure and high‐resolution thermogravimetry of liquid‐crystalline copoly(p‐oxybenzoate‐ethylene terephthalate‐p‐benzamide)

Thermotropic liquid‐crystalline copoly(ester‐amide)s consisting of three units of p‐oxybenzoate (B), ethylene terephthalate (E) and p‐benzamide (A) were studied by proton nuclear magnetic resonance at 200 and 400 MHz, wide‐angle X‐ray diffraction, and high‐resolution thermogravimetry to ascertain their molecular and supermolecular structures, thermostability and kinetics parameters of thermal decomposition in both nitrogen and air. The assignments of all resonance peaks of [¹H]NMR spectra for the copoly(ester‐amide)s are given and the characteristics of X‐ray equatorial and meridional scans are discussed. Overall activation energy data of the first major decomposition have been evaluated through three calculating techniques. The thermal degradation occurs in three steps in nitrogen and air. The degradation temperatures are higher than 447 °C in nitrogen and 440 °C in air and increase with increasing B‐unit content at a fixed A‐unit content of 5 mol%. The temperatures at the first maximum weight‐loss rate are higher than 455 °C in nitrogen and 445 °C in air and also increase with an increase in B‐unit content. The first maximum weight‐loss rates range between 11.1 and 14.5%min⁻¹ in nitrogen and between 11.9 and 13.5%min⁻¹ in air. The char yields at 500 °C in both nitrogen and air range from 45.8 to 54.3 wt% and increase with increasing B‐unit content. But the char yields at 800 °C in nitrogen and air are quite irregular with the variation of copolymer composition and testing atmosphere. The activation energy and Ln (pre‐exponential factor) for the first major decomposition are usually higher in nitrogen than in air and increase slightly with an increase in B‐unit content at a given A‐unit content of 5 mol%. The activation energy, decomposition order, and Ln (pre‐exponential factor) of the thermal degradation for the copoly(ester‐amide)s in two testing atmospheres, are situated in the ranges of 210–292 kJmol⁻¹, 2.0–2.8, 33–46 min⁻¹, respectively. The three kinetic parameters of the thermal degradation for the aromatic copoly(ester‐amide)s obtained by high‐resolution thermogravimetry at a variable heating rate are almost the same as those by traditional thermogravimetry at constant heating rate, suggesting good applicability of kinetic methods developed for constant heating rate to the variable heating‐rate method. These results indicate that the copoly(ester‐amide)s exhibit high thermostability. The isothermal decomposition kinetics of the copoly(ester‐amide)s at 450 and 420 °C are also discussed and compared with the results obtained based on non‐isothermal high‐resolution thermogravimetry. © 1999 Society of Chemical Industry     

Advanced oxidation processes for the degradation of p‐hydroxybenzoic acid 2: Photo‐assisted Fenton oxidation

Oxidation of p‐hydroxybenzoic acid in aqueous solution by the photo‐assisted Fenton reaction (Fe²⁺ + H₂O₂ + UV) has been studied. The effects of ferrous ion concentration (0.05, 0.14 and 0.29 mmol dm^?3), temperature (10, 20, 30 and 40 °C), and initial hydrogen peroxide concentration (0.7, 1.4, 2.2 and 2.9 mmol dm^?3) on the p‐hydroxybenzoic acid conversion were established. Experimental results indicate that the kinetics of this oxidation process fits pseudo‐first‐order kinetics well. The overall kinetic rate constant was split into two components: direct oxidation by UV radiation (photolysis) and oxidation by free radicals (mainly OH·) generated in the system. The importance of these two reaction paths for each specific value of ferrous ion concentration, temperature and initial hydrogen peroxide concentration was evaluated. A semi‐empirical expression is proposed for the overall reaction rate which takes into account both oxidation pathways and is a function of operating variables. © 2001 Society of Chemical Industry     

Preparation and swelling characterization of poly (n‐isopropylacrylamide)‐based porous hydrogels

Nine different poly(n‐isopropylacrylamide)‐based hydrogels, including nonionic, cationic, and anionic hydrogels, were synthesized in with and without the addition of pore‐forming agents. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observations, and the determination of the swelling ratio swelling kinetics. All the results showed that the cationic hydrogels had faster swelling kinetics than the anionic and nonionic hydrogels. The addition of pore‐forming agents (NaHCO₃ and carboxymethylcellulose) during the synthesis process led to porous hydrogels with lower dry densities, swelling ratios, and swelling kinetic parameter values. An empirical equation was developed to successfully correlate the swelling kinetic parameter with the hydrogel swelling ratio. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3651–3658, 2004     

Intrinsic and Effective Kinetics of Cobalt‐Catalyzed Fischer‐Tropsch Synthesis in View of a Power‐to‐Liquid Process Based on Renewable Energy

The production of liquid hydrocarbons based on CO₂ and renewable H₂ is a multi‐step process consisting of water electrolysis, reverse water‐gas shift, and Fischer‐Tropsch synthesis (FTS). The syngas will then also contain CO₂ and probably sometimes H₂O, too. Therefore, the kinetics of FTS on a commercial cobalt catalyst was studied with syngas containing CO, CO₂, H₂, and H₂O. The intrinsic kinetic parameters as well as the influence of pore diffusion (technical particles) were determined. CO₂ and H₂O showed only negligible or minor influence on the reaction rate. The intrinsic kinetic parameters of the rate of CO consumption were evaluated using a Langmuir‐Hinshelwood (LH) approach. The effectiveness factor describing diffusion limitations was calculated by two different Thiele moduli. The first one was derived by a simplified pseudo first‐order approach, the second one by the LH approach. Only the latter, more complex model is in good agreement with the experimental results.