Swelling properties of CMC‐g‐poly (AAm‐co‐AMPS) superabsorbent hydrogel

A series of biopolymer‐based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free‐radical graft copolymerization of acrylamide and 2‐acrylamido‐2‐methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT‐IR spectroscopy and scanning electron microscope analysis were used to confirm the hydrogel structure. Swelling measurements of the synthesized hydrogels in different salt solutions indicated considerable swelling capacity. The absorbency under load of the superabsorbent hydrogels was determined by using an absorbency under load tester at various applied pressures. A preliminary swelling and deswelling behaviors of the hydrogels were also studied. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Screening and optimization through response surface methodology for synthesis of pH,temperature and salt‐sensitive Aloe vera–acrylic acid‐based biodegradable hydrogel: Its evaluation as dye adsorbent

A pH‐, temperature‐, and salt‐sensitive hydrogel was synthesized using acrylic acid (AA) as monomer, natural polysaccharide Aloe vera as backbone, ammonium persulfate–N,N‐methylene‐bis‐acrylamide as an initiator–crosslinker system via free‐radical grafting method. Different parameters such as treatment time, temperature, amount of solvent, pH, concentration of initiator, crosslinker and monomer were screened using Plackett–Burman design (PBD). The PBD showed that pH, monomer, and crosslinker were taken as the most important variables, which highly impact the swelling behavior of the synthesized hydrogel as compared to the rest of the variables. The half normality plot was used to find the significant parameters regarding the swelling capacity of the hydrogel. The center composite design was used for further optimizing the important variables like pH, monomer, and crosslinker. The pH and monomer interaction on percentage swelling (Ps) was studied through the analysis of variance model. Synthesized hydrogel Av‐cl‐poly(AA) was characterized by different techniques such as Fourier‐transform infrared spectroscopy (FTIR), X‐ray diffraction, and scanning electron microscopy (SEM). The effect of different chloride salt solutions like KCl, NaCl, BaCl₂, FeCl₃, and CoCl₃·6H₂O on Ps of synthesized Av‐cl‐poly(AA)‐based hydrogel was also studied. Biodegradation studies of the synthesized polymer were also carried out using soil burial and vermicompositing methods. Biodegradation of semi interpenetrating polymer network (SIPN) was confirmed by SEM and FTIR techniques. Synthesized SIPN was also used as a device for the removal of dye and was found very effective as an adsorbent. POLYM. ENG. SCI., 59:2323–2334, 2019. © 2019 Society of Plastics Engineers     

Synthesis and characterization of dextran hydrogels prepared with chlor‐ and nitrogen‐containing crosslinkers

In this study, we have synthesized dextran hydrogels by the crosslinking reactions of dextran with some selective Cl‐, and N‐containing functional monomers, such as epichlorohydrin (ECH), N,N′‐methylenebisacrylamide (MBAm), and glutaraldehyde (GA). Crosslinking reactions were carried out in the basic aqueous solutions (2.8NNaOH) at 25–50°C. The optimum conditions for effective crosslinking, i.e., temperature, crosslinking time, and amount of crosslinker, were determined for each system. The hydrogel discs of 3 mm diameter and 1.5 mm thickness were subjected to a number of Tris‐buffer solutions of desired pH (2.0–9.0) at 37°C. Swelling kinetics of the hydrogels were evaluated with second–order swelling model. The pH‐dependent swelling of hydrogels was strongly influenced by the functional group of crosslinker and crosslinker content. While the hydrogels prepared with ECH and MBAm shows higher swelling ability at basic medium than that of acidic medium, GA‐containing hydrogels exhibited just the opposite behavior. Mesh sizes (ξ) and average molecular weights between crosslinks (M_c) were estimated from swelling data using the Flory‐Rehner theory. Characterization studies were completed by Fourier transform infrared spectroscopy and thermal gravimetric analysis. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4213–4221, 2006     

Swelling behaviors of ionic poly(N,N‐dimethylacrylamide‐co‐acrylamide) hydrogels in various media

Polyelectrolyte hydrogels were synthesized from N,N‐dimethylacrylamide, acrylamide, and itaconic acid with ammonium persulfate as a free‐radical initiator in the presence of methylene(bis)acrylamide as a crosslinker. The swelling behavior of the ionic poly(N,N‐dimethylacrylamide‐co‐acrylamide) hydrogels was investigated in pure water, in KSCN solutions with pHs 4 and 9, and in water–acetone mixtures according to the itaconic acid content in the hydrogel. The pulsatile swelling behavior of these hydrogels was studied both in water–acetone and in pH 2–9 buffer solutions. Although the equilibrium swelling ratio of the hydrogels with low concentrations of itaconic acid was almost not affected by changes in the temperature, the equilibrium swelling ratio of the hydrogels with high concentrations of itaconic acid increased in the temperature range of 20–50°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2140–2145, 2007     

Removal of heavy metals from model wastewater by using carboxymehyl cellulose/2‐acrylamido‐2‐methyl propane sulfonic acid hydrogels

A series of functional copolymer hydrogels composed of carboxymethyl cellulose (CMC) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) were synthesized using γ‐radiations‐induced copolymerization and crosslinking. Preparation conditions were optimized, and the swelling characteristics were investigated. The ability of the prepared hydrogels to recover some toxic metal ions from their aqueous solutions was studied. The prepared hydrogel showed a great capability to recover metal ions such as: Mn⁺², Co⁺², Cu⁺², and Fe⁺³ from their solutions. The data revealed that the chelating ability of the prepared hydrogels is mainly dependent on their internal composition, in addition to the physical properties of the metal ion solution such as pH and metal ion concentration. The data show that the chelating ability of the prepared hydrogels increases by increasing the AMPS content in the hydrogel as well as the increment in the pH of the solution and the metal ion concentration. The prepared CMC/AMPS copolymer hydrogels are chemically stable enough to be reused for at least five times with the same efficiency. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Rapid pH‐dependent phase transition and elasticity of stimuli‐responsive cationic poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli‐responsive hydrogels prepared from poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH‐dependent swelling and elasticity, a series of cationic hydrogels based on N,N‐dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH‐dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH‐dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10‐ to 40‐fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry     

Preparations and properties of thermosensitive terpolymers of N‐isopropylacrylamide,sodium 2‐acrylamido‐2‐methyl‐propanesuphonate,and N‐tert‐butylacrylamide

Terpolymers based on N‐isopropylacrylamide, sodium 2‐acrylamido‐2‐methyl‐propanesulfonate, and N‐tert‐butylacrylamide were synthesized by free‐radical copolymerization with 2,2′‐azobisisobutyronitrile as an initiator. The lower critical solution temperatures (LCSTs) of the linear polymer aqueous solutions were determined by the measurement of the transmittance on UV at different temperatures. The influence of the polymer concentration, polymer composition, and ionic strength on the LCSTs of the linear polymers was investigated. The LCST decreased with increases in the hydrophobic monomer N‐tert‐butylacrylamide, polymer concentration, and ionic strength. The phase transition became sharp when the polymer concentration and ionic strength increased. Meanwhile, the crosslinked hydrogels were prepared with the same recipe used for the linear terpolymers, but a crosslinker was added to the reaction system. The swelling ratios of the hydrogels at various temperatures and salt solutions were determined. The hydrogels possessed both high swelling ratios and thermosensitivity. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Rheological properties of poly(ethylene glycol)/poly(N‐isopropylacrylamide‐co‐2‐acrylamido‐2‐methylpropanesulphonic acid) semi‐interpenetrating networks

For the increasing demands of multifunctional materials in applications such as drug delivery system, a pH‐ and temperature‐responsive polyelectrolyte copolymer gel system was studied using rheometry. Rheological properties, determined by plate–plate rheometry in oscillatory shear, of hydrogels formed by free radical initiated copolymerization of N‐isopropylacrylamide (NIPA) and 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) in the presence of methylene bisacrylamide (MBAA) as crosslinker are compared with the properties of semi‐interpenetrating network (SIPN) polyelectrolyte gels made by incorporation of poly(ethylene glycol) with molar mass 6000 g mol^?1 (PEG6000). Based on our systematic studies for this PEG/SIPN system, the effects of initiator and crosslinker concentration, relative proportions of comonomer units in the main chains, PEG6000 content and temperature on viscoelastic properties, unusual high storage moduli at small strain for the SIPN were discussed. The SIPN gel with characteristics of PEG molecules as well as pH and temperature responsiveness from AMPS and NIPA units has potential application in drug delivery system design. Ice‐like rheological behavior of the PEG/AMPS‐NIPA SIPN gels at low temperature was first time reported and water remains homogeneous without phase separation in PEG/AMPS‐NIPA SIPN hydrogels at low temperature may be considered as an ideal candidate for water storage material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The studies on the stimuli‐response of poly (N,N‐dimethylamino ethyl methacrylate/acrylic acid‐co‐acrylamide) complex hydrogel under DC electric field

A polyelectrolyte complex hydrogel, poly (N,N‐dimethylaminoethyl methacrylate/acrylic acid‐co‐acrylamide) hydrogel designed as PDMEAA, was prepared by the free radical copolymerization in aqueous solutions. Without chemical crosslinker, PDMEAA hydrogel network was formed by electrostatic attraction of the proton‐transfer between acrylic acid and N,N‐dimethylamino ethyl methacrylate. Since the electrostatic attraction could be weakened by the application of electric field, PDMEAA hydrogel was decomposed under contacted electric field. Various factors such as gel composition, the species and concentration of electrolytes, voltage, and the experimental set‐ups, could effect the decomposing process of PDMEAA hydrogel. In CaCl₂ and MgCl₂ solutions, PDMEAA hydrogel had no change under electric field. And in high concentration of NaCl and Na₂SO₄ solutions, PDMEAA hydrogel has been eroded linearly with the increasing time applied electric field. In low concentration of NaCl and Na₂SO₄ solutions, however, a swelling process was found before the erosion. The stimuli‐responsive mechanism was investigated through scanning electron microscope (SEM) and gel permeation chromatography (GPC). © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Adsorption of surfactant by hydrophobically modified poly[2‐(diethylamino)ethylmethacrylate‐co‐N‐vinyl‐2‐pyrrolidone/octadecyl acrylate)] hydrogels and effect of surfactant adsorption on the volume phase transition

Hydrophobically modified poly[2‐(diethylamino)ethylmethacrylate‐co‐N‐vinyl‐2‐pyrrolidone/octadecyl acrylate) [P(DEAEMA‐co‐NVP/OA)] hydrogels were synthesized by free‐radical crosslinking copolymerization of 2‐(diethylamino)ethylmethacrylate (DEAEMA), N‐vinyl‐2‐pyrrolidone (NVP) with different amounts of hydrophobic comonomer octadecyl acrylate (OA) in tert‐butanol with ethylene glycole dimethacrylate (EGDMA) as a crosslinker. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). The results indicated that the swelling behavior and temperature sensitivity of the hydrogels were affected by the type and concentration of surfactant solutions. Additionally, the amount of the adsorbed SDS and DTAB molecules onto the hydrogels was determined by fluorescence measurements. An increase of OA content in the hydrogel caused an increase in the amount of adsorbed surfactant molecules in both media. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3771–3775, 2007     

Synthesis and super-swelling behavior of a novel protein-based superabsorbent hydrogel

Summary In this work, we synthesize a novel protein-based superabsorbent hydrogel and study its swelling behavior. The crosslinking graft copolymerization of acrylic acid (AA) onto the hydrolyzed collagen as a protein backbone was carried out in a homogeneous medium. Potassium persulfate (KPS) as an initiator and N,N^′-methylene bisacrylamide (MBA) as a crosslinker were used. The product’s structure was established using FTIR spectroscopy. We were systematically optimized the certain variables of the graft copolymerization (i.e. the monomer, the initiator, and the crosslinker concentration) to achieve a hydrogel with maximum swelling capacity. Under this condition, maximum capacity of swelling in distilled water was found to be 920 g/g. Morphology of the optimized sample was examined by scanning electron microscopy (SEM). The swelling ratio in various salt solutions was also determined. Additionally, the swelling of superabsorbing hydrogels was measured in solutions with pH ranged from 1 to 13. The synthesized hydrogel exhibited a pH-responsiveness character so that a swelling-collapsing pulsatile behavior was recorded at pH 2 and 8.     

Synthesis and characterization of poly{N‐[3‐(dimethylamino) propyl] methacrylamide‐co‐itaconic acid} hydrogels for drug delivery

A novel pH‐sensitive hydrogel system composed of itaconic acid (IA) and N‐[3‐(dimethylamino) propyl] methacrylamide was designed. This system was prepared by aqueous copolymerization with N,N‐methylene bisacrylamide as a chemical crosslinker. The chemical structure of the hydrogels was characterized by Fourier transform infrared (FTIR) spectroscopy. The microstructure and morphology of the hydrogels were evaluated by X‐ray diffraction (XRD) and scanning electron microscopy (SEM). The SEM study of hydrogels on higher magnification revealed a highly porous morphology with uniformly arranged pores ranging from 40 to 200 μm in size. XRD analysis revealed the amorphous nature of the hydrogels, and it was found that an increase in the IA content in the monomer feed greatly reduced the crystallinity of the hydrogels. Swelling experiments were carried out in buffer solutions at different pH values (1.2–10) at 37°C ± 1°C to investigate their pH‐dependent swelling behavior and dimensional stability. An increase in the acid part (IA) increased the swelling ratio of the hydrogels. Temperature‐sensitive swelling of the hydrogels was investigated at 20–70°C in simulated intestinal fluid. The hydrogels swelled at higher temperatures and shrank at lower temperatures. 5‐Aminosalicylic acid (5‐ASA) was selected as a model drug, and release experiments were carried out under simulated intestinal and gastric conditions. 5‐ASA release from the poly N‐[3‐(dimethylamino) propyl] methacrylamide‐co‐itaconic acid‐80 (PDMAPMAIA‐80) hydrogel was found to follow non‐Fickian diffusion mechanism under gastric conditions, and a super case II transport mechanism was found under intestinal conditions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and pH‐sensitive swelling behavior of physically crosslinked polyampholyte gels

A novel polyampholyte hydrogels were prepared by free radical aqueous copolymerization of ionic complex consisting of acrylic acid (AAc), (N,N‐diethylamino) ethyl methacrylate (DEAEM), and acrylamide (designated as PADA). Without any chemical crosslinker, the formation of PADA network structures was mainly attributed to the electrostatic interaction of AAc (anionic monomer) and DEAEM (cationic monomer). The PADA gels exhibited a typical swelling behavior of polyampholyte gels in buffer solutions. The hysteresis of isoelectric point (pI) for PADA gels was observed after preswollen in alkaline solutions. The swelling behavior of PADA gels in response to change of pH was investigated. It was found that the equilibrium swelling ratio orderly decreased in buffer solutions with alternating pH between 2.2 and 5. An abrupt swelling was observed for the hydrogels at the pH near isoelectric point in the earlier stage of swelling process. The study of swelling kinetics of the hydrogels showed that the swelling process was in agreement with the second‐order swelling kinetics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3857–3861, 2006     

Synthesis and properties of silk sericin-<Emphasis Type="Italic">g</Emphasis>-poly(acrylic acid-co-acrylamide) superabsorbent hydrogel

A novel superabsorbent hydrogel has been synthesized with the crosslinking graft copolymerization of acrylic acid (AA) and acrylamide onto the chain of silk sericin. Potassium persulfate (KPS)–sodium sulfite (NaHSO₃) as redox initiation system and N,N′-methylenebisacrylamide (MBA) as crosslinker were used. The structure of the product characterized by Fourier transform infrared absorption spectroscopy and the surface morphology of the hydrogel were observed by scanning electron microscopy. The certain parameters of the graft copolymerization including the monomer, the initiator, the crosslinker concentration, neutralization degree of AA, reaction temperature, and time were systematically optimized to achieve a hydrogel with maximum swelling capacity (2150 g/g). The optimal conditions were initiator 8 mmol/L, MBA 2.5 mmol/L, neutralization degree of AA 75%, reaction temperature 55 °C, and time 6 h. The swelling ratio in salt solutions was also determined (in 0.9% NaCl aqueous solution: 98 g/g). In addition, the swelling capability of the hydrogel was measured in solutions with pH ranged from 1 to 13. The synthesized hydrogel exhibited a pH-dependent character. Water absorbency of the product in aqueous chloride salt solutions has the Na⁺ > Ca²⁺ > Mg²⁺ > Al³⁺ order in the investigated concentration.     

pH–temperature responsive poly(HPA‐Co‐AMHS) hydrogel as a potential drug‐release carrier

In this study, a novel pH–temperature‐responsive copolymer was first synthesized by the radical copolymerization between HPA (2‐hydroxypropyl acrylate and 2‐hydroxyisopropyl acrylate) and AMHS (aminoethyl methacrylate hydrochloric salt). The molecular structure of the corresponding copolymer has been confirmed by ¹H‐NMR and FTIR. The lower critical solution temperature of the resulting copolymer exhibited a considerable dependence upon the ratio of monomers and pH value in the medium. On the basis of the copolymer, a hydrogel as drug release carrier was prepared via the introduction of a crosslinker, N,N′‐methylenebisacrylamide. The swelling behaviors of hydrogel in the different pH value, temperature, and NaCl concentration have indicated that the hydrogel showed a remarkable phase transition at 31.5°C. The swelling ratio was increased with an increasing of pH value, especially in the greater pH values. By the use of caffeine as a model drug, we investigated the caffeine‐controlled release from hydrogel systematically as a function of pH value, temperature, and crosslinker content. The caffeine release was sensitive to the temperature. Only 55% caffeine was released from the hydrogel at room temperature, whereas ～ 92% caffeine diffused into the medium at 37°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

Swelling–deswelling kinetics of poly(N‐isopropylacrylamide) hydrogels formed in PEG solutions

A series of poly(N‐isopropylacrylamide) (PNIPA) hydrogels was prepared by free‐radical crosslinking copolymerization of N‐isopropylacrylamide (NIPA) and N,N′‐methylenebisacrylamide (BAAm) in aqueous solutions of poly(ethylene glycol) of molecular weight 300 g/mol (PEG). The amount of PEG in the polymerization solvent, the crosslinker (BAAm) content, and the gel preparation temperature (T_prep) were varied in the gelation experiments. The hydrogels were characterized by the equilibrium swelling and elasticity tests as well as by the measurements of the deswelling–reswelling kinetics of the hydrogels in response to a temperature change between 25 and 48°C. The rate of deswelling of the swollen gel increases while the rate of reswelling of the collapsed gel decreases as the amount of PEG in the polymerization solvent is increased or as the crosslinker content is decreased. The T_prep effect on the swelling kinetics of the hydrogels was only observed if the PEG content of the polymerization solvent is less than 20%, which is explained with the screening of H‐bonding interactions in concentrated PEG solution. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 37–44, 2006     

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     

Synthesis and network parameters of hydrophobic poly(N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐lauryl acrylate) hydrogels

Hydrophobic poly(N‐[3‐(dimethylaminopropyl)]methacrylamide‐co‐lauryl acrylate) [P(DMAPMA‐co‐LA)] hydrogels with different LA content were synthesized by free‐radical crosslinking copolymerization of corresponding monomers in water by using N,N‐methylenebis(acrylamide) as the crosslinker, ammonium persulfate as the initiator, and N,N,N′,N′‐tetramethylethylenediamine as the activator. The swelling equilibrium of the hydrogels was investigated as a function of temperature and hydrophobic comonomer content in pure water. An interesting feature of the swelling behavior of the P(DMAPMA‐co‐LA) hydrogels with low LA content was the reshrinking phase transition where the hydrogels swell once and collapse as temperature was varied in the range of 30–40°C. The average molecular mass between crosslinks (M?_c) and polymer–solvent interaction parameter (χ) of the hydrogels were calculated from equilibrium swelling values. The enthalpy (ΔH) and entropy (ΔS) changes appearing in the χ parameter for the hydrogels were determined by using the Flory–Rehner theory based on the phantom network model of swelling equilibrium. The positive values for ΔH and ΔS indicated that the hydrogels had a positive temperature‐sensitive property in water, that is, swelling at a higher temperature and shrinking at a lower temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4159–4166, 2006