Swelling behavior of poly(acrylamide‐co‐N‐vinylimidazole) hydrogels under different environment conditions

A series of random copolymers of acrylamide and N‐vinylimidazole, poly(AAm‐co‐NVI), with various compositions were prepared using redox copolymerization. The influence of environmental conditions such as pH, temperature, and ionic strength on the swelling behavior of the copolymeric hydrogels was investigated. The hydrogels exhibited the highest equilibrium swelling in basic medium at high temperature. Equilibrium swelling decreased with rising ionic strength at pH 5.0. As pH increased, equilibrium swelling of the hydrogels increased at pH 11.0 and I = 0.20 M. Swelling kinetics of the hydrogels was found to be non‐Fickian at 25°C. The process tended to be Fickian at higher pH and temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1783–1788, 2005     

Preparation and characterization of a novel pH‐, thermo‐, and ionic strength‐responsive hydrogels based on xanthan gum–poly(aspartic acid)

A series of interpenetrating polymer networks (IPN) hydrogels with different compositions that based on xanthan gum (XG) and poly(aspartic acid) (PASP) were synthesized. The effects of various external surrounding stimuli, including pH, temperature, and ionic strength on XG–PASP hydrogels swelling properties were investigated. Chemical structural changes of the IPN hydrogels were characterized by Fourier transform infrared spectroscopy (FT‐IR), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and swelling ratio measurement. The swelling process was found to be a Fickian diffusion and reached swelling equilibrium quickly. It was found that the feed composition of PASP was an important factor that affected the properties of IPN hydrogels. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of pH‐ and salt‐responsive hydrogels based on etherificated sodium alginate

Hydrogels composed of etherificated sodium alginate (ESA), sodium acrylic acid (NaAA), and poly (vinyl alcohol) (PVA) were synthesized by aqueous solution polymerization. The effects of reaction variables such as terminal pH, ions, and ionic strength on hydrogel swelling ratio (SR) were determined and compared. SR was influenced strongly by pH and ionic strength. SR increased with increasing pH but tended to decrease with PVA content. At a given ionic strength, SR of ESA/NaAA/PVA hydrogel was dependent on the valence of anion; SR was higher in multivalent anion salt solution than in monovalent anion salt solution, i.e., SR_K2SO4 > SR_KCl and SR_Na2SO4 > SR_NaCl. The swelling kinetic of the hydrogels showed Fickian kinetic diffusion in acidic media and non‐Fickian behavior in alkaline media. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Swelling behaviour of a new kind of polyampholyte hydrogel composed of dimethylaminoethyl methacrylate and acrylic acid

Poly[(dimethylaminoethyl methacrylate)‐co‐(acrylic acid)] [poly(DMAEMA‐co‐AAc)] hydrogels have been synthesized by UV‐induced copolymerization of dimethylaminoethyl methacrylate (DMAEMA) and acrylic acid monomer. The effects of pH and ionic strength on the swelling behaviour of poly(DMAEMA‐co‐AAc) hydrogels were investigated in detail. It was found that there is minimal equilibrium swelling ratio (ESR) for the hydrogels with the change of pH, and the pH at minimal ESR of the hydrogels was defined by the isoelectric points (IEP), similar to the situation with protein molecules. The IEP of the hydrogels shifted to higher values with increase in the DMAEMA content in the hydrogels. Antipolyelectrolyte behaviour of the hydrogels at a pH near the IEP was observed as well, and the ESR increased with increasing ionic strength. The study of swelling kinetics of the hydrogels showed that the swelling process was Fickian at the IEP and non‐Fickian when the pH deviated from the IEP. Copyright © 2003 Society of Chemical Industry     

Radiation synthesis and characterization of 2‐hydroxyethyl‐methacrylate‐based hydrogels containing di‐ and tri‐protic acid and its application on wastewater treatment

Radiation‐crosslinked 2‐hydroxyethylmethacrylate/citric acid (HEMA/CAc), 2‐hydroxyethylmethacrylate/tartaric acid (HEMA/TA), and 2‐hydroxyethylmethacrylate/succinic acid (HEMA/Sc) copolymers were prepared by using ⁶⁰Co γ‐rays. The gel fraction yield and the swelling behavior of the prepared hydrogels were studied. It was shown that increasing irradiation doses was accompanied by an increase in yield of gel fraction and a decrease in swelling degree. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, swelling exponent, and diffusion coefficient of the hydrogels were determined by studying the swelling behavior of the hydrogels prepared. It was seen that the equilibrium swelling degree increases as the content of acid increases, as a result of introducing more hydrophilic groups. When the hydrophilic polymer (acids) varies in the content range of 40–80 mg, swelling exponents (n) decreases, thereby indicating a shift in the water‐transport mechanism from the anomalous (non‐Fickian)‐type to the Fickian‐type. Characterization and some selected properties of the prepared hydrogels were studied, and accordingly the possibility of its practical use in the treatment of industrial wastes such as dyes and heavy metals (Fe, Ni, Co, and Cu) were also studied. The effect of treatment time, pH of feed solution, initial feed concentration, and temperature on the dye and heavy metals uptake was determined. The uptake order for a given metal was HEMA/TA hydrogel > HEMA/CAc > HEMA/Sc hydrogel. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Hydrogels for oral drug delivery of peptides: Synthesis and characterization

In this study hydrogels were synthesized by the copolymerization of acrylamide and itaconic acid in the presence of poly(N‐vinyl‐2‐pyrrolidone) in an aqueous medium. The incorporation of a small amount of itaconic acid resulted in the transition of the swelling behavior from Fickian to non‐Fickian. The hydrogels showed good response to the valency of the counterions and pH of the swelling media. The equilibrium water uptake increased with the pH of the external solution, thus attaining a maximum value at pH 7–8. The gels exhibited a number of deswelling–swelling cycles while maintaining mechanical strength and shape stability. The amount of itaconic acid present in the system affected the swelling behavior of the hydrogels in a rather unusual way. At pH 2.0 the equilibrium water uptake increased with the amount of acid monomer up to 15 mM, remained almost constant for a very small range of concentrations (i.e., up to 22 mM), and then finally decreased with the further increase of the acid content. However, a continuous increase was observed at the pH 7.0 of the swelling media. The hydrogels showed very poor temperature dependency and the activation energies for the samples with and without itaconic acid were 29.09 and 19.92 kJ mol^?1, respectively. Finally, the swelling and deswelling processes were explained on the basis of two different mechanisms that were followed by the gels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1717–1729, 2002     

Radiation Induced Superabsorbent Hydrogels. Acrylamide/Itaconic Acid Copolymers

Acrylamide/itaconic acid hydrogels in the form of rods are prepared by γ‐irradiation of ternary mixtures of acrylamide/itaconic acid/water with 2.00–5.71 kGy γ‐rays. Spectroscopic and thermal characterization of the copolymers were examined. Dynamic and equilibrium swelling behavior of superabsorbent acrylamide/itaconic acid hydrogels was investigated in water. The equilibrium swelling degree, the swelling rate coefficient, the diffusion constant, the diffusion exponent, the diffusion coefficient, and the intrinsic diffusion coefficient of acrylamide/itaconic acid hydrogels were calculated. The superabsorbent hydrogels have shown mass swelling capabilities in the range 650–700% (for polyacrylamide hydrogels) and 900–2100% (for acrylamide‐itaconic acid hydrogels). Diffusion type of the hydrogels is non‐Fickian diffusion. The equilibrium swelling studies were used to determine important parameters of the crosslinked structure of the hydrogels, including the average molar mass between crosslinks and crosslink density.     

The effect of PEG(400)DA crosslinking agent on swelling behaviour of acrylamide-maleic acid hydrogels

Summary Acrylamide (AAm)-maleic acid (MA) hydrogels with different monomer ratios were prepared in an aqueous solution by radical polymerization using a new crosslinking agent, polyethyleneglycol (400) diacrylate (PEG (400) DA) and also using N, N’-methylenebisacrylamide (NMBA) for comparison purpose. The hydrogels were characterized by acid group content and FTIR spectroscopy. Their swelling and deswelling behavior were studied as a function of maleic acid content, pH and crosslinking agent. Incorporation of MA in hydrogels significantly increased their swelling ability and their equilibrium degree of swelling (EDS) values changed between 100–269 g water/g polymer in water while AAm polymers swollen less (22–23 g water/g polymer). The AAm hydrogels showed Fickian type diffusion but the all AAm-MA hydrogels showed non-Fickian type behavior. Their swelling degree increased with the increase of pH of the external medium and an instantaneous increase was observed near a pH value of 7.0. The use of PEG (400) DA instead of NMBA as a crosslinking agent also increased the swelling rate and capacity of the gel. The swelling constant (K) and the diffusion coefficient (D) of hydrogels were also increased. The swelling-deswelling cycles in acidic-basic solutions showed that they could be used as pH responsive gels without any decrease in swelling capacity.     

Removal of methylene blue dyes from wastewater using cellulose‐based superadsorbent hydrogels

Superadsorbent cellulose‐graft‐acrylic acid (C‐g‐AA) hydrogels were successfully prepared via free radical polymerization in phosphoric acid solution. Phosphoric acid solution provides a homogeneous reaction system. The C‐g‐AA hydrogels have a porous network inner structure with cellulose as the backbone. The introduced carboxyl groups enable the C‐g‐AA hydrogels with good swelling property (swelling ratio 7327%) and excellent MB adsorption capacity (equilibrium adsorption amount 2197 mg g^?1). The dynamic swelling behaviors of the hydrogels were tested, water intake of hydrogels followed a non‐Fickian type diffusion. The effects of mole ratio of AA to cellulose, the pH of adsorption medium and the initial MB concentration on dye adsorption capacity of hydrogels were investigated. The adsorption isotherm and kinetics fit the Langmuir model and the Pseudo‐second‐order model well, respectively. Desorption was carried out in weak acid solution and 70% MB could be removed, suggesting the C‐g‐AA hydrogels had the potential for reuse. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

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     

External Stimuli‐Responsive Characteristics of Ionic Poly[(N,N‐diethylaminoethyl methacrylate)‐co‐(N‐vinyl‐2‐pyrrolidone)] Hydrogels

Summary: Polyelectrolyte hydrogels containing diprotic acid moieties sensitive to ionic strength changes of the swelling medium were synthesized from N,N‐diethylaminoethyl methacrylate (DEAEMA), N‐vinyl‐2‐pyrrolidone (VP) and itaconic acid (IA) by using ammonium persulfate (APS) as a free radical initiator in the presence of the cross‐linker, methylenebisacrylamide (MBAAm). The swelling behavior of the ionic poly[(N,N‐diethylaminoethyl methacrylate)‐co‐(N‐vinyl‐2‐pyrrolidone)] [P(DEAEMA/VP)] hydrogels were investigated in pure water; in NaCI solutions with pH 4 and 9; and in water‐acetone mixtures depending on the IA content in the hydrogel. The average molecular mass between cross‐links ( ) and polymer‐solvent interaction parameter (χ) of the hydrogels were determined from equilibrium swelling values. The pulsatile swelling behavior was also observed in response to solvent changes between the solution in water and in acetone. The equilibrium swelling ratio of these hydrogels was basically unaffected with change in temperature. The swelling variations were explained according to the swelling theory based on the hydrogel chemical structure.

Pulsatile swelling behavior of ionic P(DEAEMA/VP) hydrogels in response to solvent changes between water and acetone at 25 °C.     

Enzymatically degradable and pH‐sensitive hydrogels for colon‐targeted oral drug delivery. I. Synthesis and characterization

Cylindrical hydrogels, composed of starch and poly(acrylic acid), were synthesized, and their swelling behavior was studied as a function of the pH of the medium. The gels underwent a sharp transition from Fickian swelling behavior (swelling exponent n = 0.30) to non‐Fickian swelling behavior (n = 0.96) as the pH of the swelling medium changed from 2.0 to 7.4. The hydrogels also underwent partial enzymatic degradation in an amylase‐containing medium of pH 7.4 at 37°C. The effects of the enzyme concentration in the swelling media, the amount of starch present in the gel, the initial water content, the degree of crosslinking, and the diameter of cylindrical hydrogels on the degradation behavior were studied. The degradation of the gels followed Michaelis–Menten kinetics, and the value of the Menten constant was 41.62 × 10^?2. The gels exhibited minimum swelling in an acidic pH medium through the formation of a complex hydrogen‐bonded structure and underwent enzymatic degradation in a medium of pH 7.4 (i.e., simulating intestinal fluid) along with chain‐relaxation‐controlled swelling. Therefore, the gels have potential for colon‐targeted drug delivery. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3630–3643, 2004     

Dynamic swelling behavior of pH‐sensitive anionic hydrogels used for protein delivery

There have been many attempts to use anionic hydrogels as oral protein delivery carriers because of their pH‐responsive swelling behavior. The dynamic swelling behavior of poly(methacrylic acid‐co‐methacryloxyethyl glucoside) and poly(methacrylic acid‐g‐ethylene glycol) hydrogels was investigated to determine the mechanism of water transport through these anionic hydrogels. The exponential relation M_t/M_∞ = ktⁿ (where M_t is the mass of water absorbed at time t and M_∞ is the mass of water absorbed at equilibrium) was used to calculate the exponent (n) describing the Fickian or non‐Fickian behavior of swelling polymer networks. The mechanism of water transport through these gels was significantly affected by the pH of the swelling medium. The mechanism of water transport became more relaxation‐controlled in a swelling medium of pH 7.0, which was higher than pK_a of the gels. The experimental results of the time‐dependent swelling behaviors of the gels were analyzed with several mathematical models. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1606–1613, 2003     

pH/temperature‐responsive semi‐IPN hydrogels composed of alginate and poly(N‐isopropylacrylamide)

Amino semitelechelic poly(N‐isopropylacrylamide) (PNIPAAm) was prepared by radical polymerization with aminoethanethiol hydrochloride as a chain‐transfer agent. Semi‐interpenetrating polymer network (semi‐IPN) hydrogels, composed of alginate and amine‐terminated PNIPAAm, were prepared by crosslinking with calcium chloride. From the swelling behaviors of semi‐IPNs at various pH's and Fourier transform infrared spectra at high temperatures, the formation of a polyelectrolyte complex was confirmed from the reaction between carboxyl groups in alginate and amino groups in modified PNIPAAm. Semi‐IPN hydrogels reached an equilibrium swelling state within 24 h. The water state in hydrogels, investigated by differential scanning calorimetry, showed that sample CAN55 [alginate/PNIPAAm (w/w) = 50/50] exhibited the lowest equilibrium water content and free water content among the hydrogels tested, which was attributed to its more compact structure compared to other samples and the high content of interchain bonding within the hydrogels. Alginate/PNIPAAm semi‐IPN hydrogels exhibited a reasonable sensitivity to the temperature, pH, and ionic strength of swelling medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1128–1139, 2002     

Preparation of poly(acrylic acid‐co‐acrylamide)/kaolin and release kinetics of urea from it

A series of poly(acrylic acid‐co‐acrylamide)/kaolin [poly(AA‐co‐Am)/kaolin] composites were prepared by aqueous solution copolymerization of partially neutralized acrylic acid and acrylamide in the presence of kaolin nanopowder, which was synthesized to act as a release carrier of urea fertilizer. The superabsorbent composite was swollen in aqueous solution of urea to load urea, and the effect of urea concentration on the swelling was investigated. Furthermore, the effects of the contents of crosslinker, kaolin, and acrylamide, the neutralization degree of acrylic acid, and temperature, pH, and ionic strength of release medium on water absorbency and diffusion coefficient of urea release from poly(AA‐co‐Am)/kaolin were studied systematically. It was found that urea loading percentage could be adjusted by urea concentration of swelling medium, and urea diffusion coefficient could be regulated through the contents of crosslinker, kaolin, and acrylamide, and the neutralization degree of acrylic acid. Additionally, temperature and ionic strength of release medium may also affect the urea release process. The conclusions obtained could provide theoretical basis for urea diffusion behavior in superabsorbent used in agriculture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and characterization of novel polyglycerol hydrogels containing L‐lactic acid groups as pendant acidic substituents: pH‐Responsive polyglycerol‐based hydrogels

Novel pH‐responsive polyglycerol (PG)‐based hydrogels were successfully synthesized through the reaction of epichlorohydrin with L ‐lactic acid (LLA) in the presence of sodium hydroxide (NaOH), and cetyltrimethylammonium bromide as a phase transfer catalyst at room temperature, followed by hydrolysis, polymerization, and crosslinking reactions. The resultant gel was characterized by carbon nuclear magnetic resonance spectroscopy, X‐ray photoelectron spectroscopy, and Fourier transform infrared measurement, and it was found that incorporated LLA was bound to PG network as a pendant acidic substituent by the hydroxyl group of LLA (PGL gel). The PGL hydrogels with different LLA contents and equilibrium swelling ratios (ESRs) were prepared by changing the feed ratios of materials. The results determined by chemical titration showed that under the applied conditions the efficiency of introducing the carboxyl group into PG network was about 86% and the amount of LLA in the hydrogel reached to about 17 wt %. The swelling behavior of the hydrogels in different environmental mediums was investigated, and the results showed that the hydrogels are pH‐, ionic strength‐, and cationic charge‐responsive. The hydrogels also have the reversible swelling/deswelling properties. These pH‐responsive PG‐based hydrogels will have potential applications in biomedical and related areas. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling and diffusion characteristics of novel semi‐interpenetrating network hydrogels composed of poly[(acrylamide)‐ co‐(sodium acrylate)] and poly[(vinylsulfonic acid), sodium salt]

A series of novel semi‐interpenetrating polymer networks (IPNs) composed of poly[(acrylamide)‐co‐(sodium acrylate)] with varying amounts (5, 10, and 15 wt%) of poly[(vinylsulfonic acid), sodium salt] was synthesized. The semi‐IPN hydrogels were characterized by infrared spectroscopy. The swelling behavior of these IPNs was studied in distilled water/physiological solutions/buffer solutions/salt solutions. As the amount of poly[(vinylsulfonic acid), sodium salt] increased in the network, the swelling capacity of the semi‐IPNs increased considerably. The swelling and diffusion characteristics such as water penetration velocity (v), diffusion exponent (n), and diffusion coefficient (D) were calculated in distilled water, as well as in other physiological solutions. The highest swelling capacity was noted in urea and glucose solutions. The semi‐IPN hydrogels followed non‐Fickian diffusion behavior in water and physiological fluids, whereas Fickian behavior was observed in buffer solutions. The stimuli‐responsive characteristics towards physiological fluids, salt concentration, and temperature of these semi‐IPN hydrogels were also investigated. The swelling behavior of the semi‐IPNs decreased markedly with an increase of the concentration of the salt solutions. Copyright © 2006 Society of Chemical Industry     

pH‐sensitive hydrogels based on bovine serum albumin for anticancer drug delivery

Protein conjugates consisting of hydroxyethyl methacrylate and acrylic acid monomers in the presence of bovine serum albumin (BSA) were prepared by gamma irradiation to examine the potential use of these hydrogels in the controlled drug release systems. The study parameter was the BSA content in the as‐prepared conjugates. Polymers were characterized with FTIR, scanning electron microscopy (SEM), and swelling studies. The polymerization reaction caused the rearrangement of the BSA carbonyl hydrogen bonding and finally led to the modification of the BSA secondary structure as proved by FTIR. SEM proved that the prepared conjugates matrices are porous, with a three‐dimensional interconnected microstructure. The swelling kinetics of the hydrogels and the release dynamics of an anticancer model drug (flutamide) have been studied. High equilibrium swelling values, up to 1550%, could be observed and were correlated with the increase in pH, temperature, and BSA content. The mechanism of swelling changed from Fickian to non‐Fickian by reducing the acidity of the medium. This study proved that there is a direct relationship between the protein content in the conjugates and both the loaded and the released drug. These pH responsive conjugates may be exploited for the delivery of flutamide. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of novel pH‐sensitive chitosan‐poly(acrylamide‐co‐itaconic acid) hydrogels

Novel pH‐sensitive chitosan‐poly(acrylamide‐co‐itaconic acid) hydrogels were prepared by free radical copolymerization of acrylamide and itaconic acid (IA) in chitosan solution. The hydrogels were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and the swelling ratios of the hydrogels in water (pH 6.8) and pH 1.2. The influence of composition on the thermal properties of the hydrogels was assessed. The glass transition temperatures of the samples increased with IA content, ranging from 110 to 136 °C. Swelling of the hydrogels was found to obey second‐order kinetics with respect to the remnant swelling, indicating that diffusion is controlled by the relaxation of chains. The equilibrium swelling degree was strongly dependent on pH and composition. At both pH values the highest water uptake was obtained for the IA‐free sample M1. From the equilibrium swelling results the average molar mass between crosslinks, M_c, and the crosslink density of the chitosan‐poly(acrylamide‐co‐itaconic acid) samples were calculated. The results evidenced the reinforcing effect of IA on the hydrogel structure. It is concluded that these highly swellable pH‐sensitive hydrogels can be useful for applications in biomedicine and pharmacy. © 2013 Society of Chemical Industry     

Synthesis of copolymeric hydrogels using gamma radiation and their utilization in the removal of some dyes in wastwater

Copolymer hydrogels were prepared by γ‐radiation copolymerization of maleic acid (MA) and 2‐hydroxyethylacrylate (HEA) or acrylamide (AAm). The effect of AAm/MA and HEA/MA composition and irradiation dose on the gel fraction yield in the prepared hydrogels was determined. It was found that as the content of MA increased, the gel fraction yield decreased. The increase of irradiation dose resulted in increasing the crosslinked network structure and consequently the gel percent. The parameters of equilibrium swelling, maximum swelling, initial swelling rate, diffusion exponent, and diffusion coefficient of the hydrogels were calculated and evaluated, and it was found that water diffusion to the hydrogels generally was a non‐Fickian diffusion type. Characterization of the prepared hydrogels was studied and accordingly the possibility of its practical use in the treatment of waste dyes from aqueous solution was studied. The effect of treatment time, the pH of the feed solution, initial feed concentration, and temperature on the dye uptake was also investigated. The maximum uptake of the investigated dyes was higher for HEA/MA hydrogel than that for AAm/MA hydrogel. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3720–3731, 2006