Fast responsive poly(acrylic acid‐co‐N‐isopropyl acrylamide) hydrogels based on new crosslinker

Novel dual temperature‐ and pH‐sensitive poly(acrylic acid‐co‐N‐isopropylacrylamide), AA/NIPAAm, hydrogels were successfully prepared by chemical crosslinking with crosslinkers. Copolymers of AA/NIPAAm were crosslinked in the presence of different mol % of N,N‐methylene bisacrylamide (MBA) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked AA/NIPAAm series are evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MBA concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. The prepared MAAm type AA/NIPAAm hydrogels exhibited a more rapid deswelling rate than MBA type AA/NIPAAm hydrogels in ultra pure water in response to abrupt changes from 20°C to 50°C. The results of this study provide valuable information regarding the development of dual stimuli‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

CO2‐responsive swelling behavior and metal‐ion adsorption properties in novel histamine‐conjugated polyaspartamide hydrogel

Novel polyaspartamide copolymers containing histamine pendants (PHEA‐HIS) were prepared from polysuccinimide, which is the thermal polycondensation product of aspartic acid, via a successive ring‐opening reaction using histamine (HIS) and ethanolamine (EA). The prepared water‐soluble copolymer was then crosslinked by reacting it with hexamethylene diisocyanate in order to provide a hydrogel with both good gel strength and reversible CO₂ absorption characteristics. PHEA‐HIS gel is also pH‐sensitive and eligible to coordinate to metal ions such as Pb²⁺, Cu²⁺, and Ni²⁺ due to the imidazole units in its structure. The CO₂‐responsive swelling behavior, metal‐ion adsorption, and morphology of the crosslinked gels were investigated. The approach described here results is a promising hydrogel with potential for a variety of industrial and biomedical applications including CO₂ capture, CO₂‐responsive and switchable sensors, and smart drug delivery systems. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43305.     

Improved swelling–deswelling behavior of poly(N‐isopropyl acrylamide) gels with poly(N,N′‐dimethyl aminoethyl methacrylate) grafts

Thermoresponsive and pH‐responsive gels were synthesized from N‐isopropyl acrylamide (NIPA) and N,N′‐dimethyl aminoethyl methacrylate (DMAEMA) monomers. Gelation reactions were carried out with both conventional free‐radical polymerization (CFRP) and controlled free‐radical polymerization [reversible addition fragmentation transfer (RAFT)] techniques. The CFRP gels were prepared by polymerizing mixtures of NIPA and DMAEMA in 1,4‐dioxane in presence of N,N'‐methylene bisacrylamide (BIS) as cross‐linker. The RAFT gels were prepared by a the polymerization of NIPA via a similar process in the presence of different amounts of poly(N,N′‐dimethyl aminoethyl methacrylate) macro chain‐transfer agent and the crosslinker. These gels were characterized by scanning electron microscopy (SEM) and differential scanning calorimetry. SEM analysis revealed a macroporous network structure for the RAFT gels, whereas their volume phase‐transition temperatures (VPTTs) were found to be in the range 32–34°C, close to that of poly(N‐isopropyl acrylamide) gels. However, the CFRP copolymer gels exhibited a higher VPTT; this increased with increasing DMAEMA content. The RAFT gels exhibited higher swelling capabilities than the corresponding CFRP gels and also showed faster shrinking–reswelling behavior in response to changes in temperature. All of the gels showed interesting pH‐responsive behavior as well. The unique structural attributes exhibited by the RAFT gels can potentially open up opportunities for developing new materials for various applications, for example, as adsorbents or carrier of drugs or biomolecules. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42749.     

pH‐reversible hydrogels. IV. Swelling behavior of the 2‐hydroxyethyl methacrylate‐co‐acrylic acid‐co‐sodium acrylate copolymeric hydrogels

A series of 2‐hydroxyethyl methacrylate (HEMA) and sodium acrylate (SA50) copolymeric gels were prepared from HEMA and the anionic monomer SA50 with various molar ratios. The influence of SA50 on the copolymeric gels on their swelling behavior in deionized water at different temperatures and various pH buffer solutions was investigated. Results indicated that the poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogels exhibited an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreased with increasing of the temperature. The same results were also found in the HEMA/SA50 copolymeric gels with a lower SA50 content. On the contrary, the overshooting phenomenon for HEMA/SA50 copolymeric gels with a higher content of SA50 was exhibited only under higher temperature (over 35°C). These copolymer gels were used to assess drug release and drug delivery in this article. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1360–1371, 2001     

Salt and pH sensitive semi‐interpenetrating polyelectrolyte hydrogels poly(HEMA‐co‐METAC)/PEG and its BSA adsorption behavior

A novel semi‐interpenetrating poly(2‐hydroxyethyl methacrylate) (pHEMA) based polyelectrolyte hydrogel [p(HEMA‐co‐METAC)/PEG] was prepared by copolymerizing HEMA with the cationic monomer 2‐methacryloyloxyethyltrimethyl ammonium chloride (METAC) in the presence of polyethylene glycol (PEG) with different content and molecular weight (MW 4000 and 400). The chemical structure of the gels was confirmed by FT‐IR spectroscopy, morphology study was performed by scanning electron microscope (SEM), thermal stability was revealed by thermogravimetric analysis (TGA), and the mechanical properties were determined by electronic universal testing machine. Swelling studies showed introduction of cationic monomer METAC led to high water content, and the obvious salt and pH sensitive properties were observed which proved the smart behavior of the semi‐interpenetrating polymer networks (IPNs) gels. In addition, the effect of temperature and some important biological solution on swelling behavior were reported. Cytotoxicity test demonstrated that synthesized gels owned satisfactory cytocompatibility and were convenient for the application as biomaterials. Finally, the weak bovine serum albumin (BSA) adsorption on semi‐IPNs by introducing METAC and controlling the content of PEG in gels demonstrated that they were of good protein resistance effect in biomedical applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41537.     

Synthesis and characterization of 2‐hydroxyethylmethacrylate/2‐(3‐indol‐yl)ethylmethacrylamide‐based novel hydrogels as drug carrier with in vitro antibacterial properties

In this study, a new cationic monomer 2‐(3‐indol‐yl)ethylmethacrylamide (IEMA) derived from tryptamine was synthesized in a single step and characterized by Fourier transform infrared (FTIR), ¹H‐NMR, and ¹³C‐NMR. Then, one‐step preparation of novel poly[2‐hydroxyethylmethacrylate‐c‐2‐(3‐indol‐yl)ethylmethacrylamide], or p(HEMA‐c‐IEMA), copolymeric hydrogels has been performed successfully with IEMA and 2‐hydroxyethylmethacrylate (HEMA) as monomers using free radical aqueous polymerization. The hydrogels were characterized with scanning electron microscopy, FTIR, elemental analysis, thermogravimetric analysis, and texture profile analysis instruments. p(HEMA‐c‐IEMA) hydrogels were used for swelling, diffusion, drug release, and antibacterial activity studies. The drug‐release behavior of the hydrogels was determined as a function of time at 37 °C in pH 1.2 and 7.2. The swelling and drug‐release studies showed that an increased IEMA amount caused a higher increase in swelling and drug‐release values. Additionally, zero‐order, first‐order, and Higuchi equation kinetic models were applied to the drug‐release data, and the data fit well in the Higuchi model, and the Peppas power‐law model was applied to the release mechanism. Finally, the antibacterial activities of the hydrogels were screened against Gram‐positive bacteria (Bacillus cereus and Staphylococcus aureus) and Gram‐negative bacteria (Escherichia coli and Salmonella typhimurium). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45550.     

pH‐thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N‐isopropylacrylamide‐co‐acrylamide‐co‐2‐hydroxyethyl methacrylate) copolymeric hydrogels

A series of pH‐thermoreversible hydrogels that exhibited volume phase transition was synthesized by various molar ratios of N‐isopropylacrylamide (NIPAAm), acrylamide (AAm), and 2‐hydroxyethyl methacrylate (HEMA). The influence of environmental conditions such as temperature and pH value on the swelling behavior of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios in different pH solutions. Amide groups could be hydrolyzed to form negatively charged carboxylate ion groups in their hydrophilic polymeric network in response to an external pH variation. The pH sensitivities of these gels also depended on the AAm content in the copolymeric gels; thus the greater the AAm content, the higher the pH sensitivity. These hydrogels, based on a temperature‐sensitive hydrogel, demonstrated a significant change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a dehydrated network response to small variations of temperature. pH‐thermoreversible hydrogels were used for a study of the release of a model drug, caffeine, with changes in temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 221–231, 1999     

Synthesis and swelling properties of 2‐hydroxyethyl methacrylate‐co‐1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine hydrogels

A series of 2‐hydroxyethyl methacrylate/1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine (HEMA/VSIB) copolymeric gels were prepared from various molar ratios of HEMA and the zwitterionic monomer VSIB. The influence of the amount of VSIB in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures and the drug‐release behavior, compression strength, and crosslinking density were investigated. Experimental results indicated that the PHEMA hydrogel and the lower VSIB content (3%) in the HEMA/VSIB gel exhibited an overshooting phenomenon in their dynamic swelling behavior, and the overshooting ratio decreased with increase of the temperature. In the equilibrium water content, the value increased with increase of the VSIB content in HEMA/VSIB hydrogels. In the saline solution, the water content for these gels was not affected by the ion concentration when the salt concentration was lower than the minimum salt concentration (MSC) of poly(VSIB). When the salt concentration was higher than the MSC of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. However, the swelling behavior of gels in KI, KBr, NaClO₄, and NaNO₃ solutions at a higher concentration would cause an antipolyelectrolyte phenomenon. Besides, the anion effects were larger than were the cation effects in the presence of a common anion (Cl^?) with different cations and a common cation (K⁺) with different anions for the hydrogel. In drug‐release behavior, the addition of VSIB increased the drug‐release ratio and the release rate. Finally, the addition of VSIB in the hydrogel improved the gel strength and crosslinking density of the gel. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2888–2900, 2001     

Hydrogel characteristics of a novel temperature‐sensitive polymer,poly(N‐2‐methoxyisopropylacrylamide)

In this study, a novel temperature‐sensitive polymer, poly(N‐2‐methoxyisopropylacrylamide), PNMIPA, in the crosslinked hydrogel form was obtained. The monomer, N‐2‐methoxyisopropylacrylamide (NMIPA) was synthesized by the nucleophilic substitution reactions of acryloyl chloride with 2‐methoxyisopropylamine. Hydrogel matrix of PNMIPA was obtained by the bulk polymerization method. The bulk polymerization experiments were performed at +4°C, by using N,N‐methylenebisacrylamide (MBA) as crosslinker, polyethyleneglycol (PEG) 4000 as diluent, and potassium persulfate (KPS) and tetramethylethylenediamine (TEMED) as the initiator and accelerator, respectively. The same polymerization procedures were applied by changing monomer, initiator, crosslinker and diluent concentrations in order to obtain crosslinked gel structures having different temperature–sensitivity properties. The equilibrium swelling ratio of PNIMPA gel matrices at constant temperature increased with increasing initiator concentration and decreasing monomer concentration. The use of PEG 4000 as diluent in the gel synthesis resulted in about two times increase in equilibrium swelling ratios in the low temperature region. A decrease in the equilibrium swelling ratios of gel matrices started at 30°C and the decrease became insignificant at 55°C. Temperature‐sensitivities were determined in two different media. Distilled water medium was used in order to observe the temperature‐sensitivity of the gel clearly and the phosphate buffer medium was used in order to represent the temperature‐sensitive swelling behavior of the gel when it is used in biological media. Step effect was applied on ambient temperature in two opposite directions in order to examine the dynamic swelling and shrinking behaviors of the gels. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of pH‐Sensitive Networks by Ultraviolet Induced Crosslinking of Poly(ethylene oxide)‐Poly(2‐vinylpyridine) Blends

Blends of poly(ethylene oxide) of molecular weight 1 000 000 and poly(2‐vinylpyridine) of molecular weight 300 000 were crosslinked by exposure to ultraviolet radiation at 25, 75 and 115°C in the presence of benzophenone as a hydrogen‐abstracting agent. The crosslinking efficiency as well as the pH sensitivity strongly depend on the blend composition, the concentration of benzophenone and the irradiation temperature. The equilibrium swelling behavior of the mixed networks in aqueous solution was studied as a function of pH at constant ionic strength. A more pronounced swelling transition upon pH changes from 2 to 7 is observed at greater content of P2VP in the networks. The addition of poly(propylene oxide) to the P2VP‐PEO networks leads to enhanced mechanical strength and to much greater swelling dependence on pH, due to the hydrophobic and elastic nature of PPO.     

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     

Study of poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels made using gamma radiation initiation

Poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels were synthesized using gamma‐radiation‐initiated polymerization. The progress of copolymerization and crosslinking was observed by viscosity measurement on reaction mixtures subjected to varying radiation doses. The copolymer gels were characterized by differential scanning calorimetry, X‐ray diffraction, scanning electron microscopy, infrared spectroscopy, and elemental analysis. The swelling behavior and other properties of the gels were found to be very similar to those of poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropane sulfonic acid) hydrogels synthesized using conventional free‐radical initiation in the presence of crosslinkers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1322–1330, 2003     

Kinetic analysis of the swelling behavior of poly(n‐butylacrylate‐1,6‐hexanedioldiacrylate) networks in 4‐cyano‐4′‐n‐pentyl‐biphenyl (5CB)

The dynamic swelling behavior of chemically crosslinked poly(n‐butylacrylate/1,6‐hexanedioldiacrylate) [poly(Abu‐HDDA)] networks, immersed in an nematogenic and two isotropic solvents, was experimentally analyzed. These networks were elaborated by ultraviolet (UV)–visible light‐induced radical polymerization/crosslinking reactions of Abu/HDDA mixtures, to yield poly(Abu/0.5 wt % HDDA) and poly(Abu/5 wt % HDDA) networks corresponding to weakly and strongly crosslinked systems, respectively. The swelling behavior of these poly(Abu‐HDDA) networks was investigated by immersion in excess solvent, followed by subsequent measurements of the variation of the sample size by means of optical microscopy, depending on temperature and immersion time. Methanol and toluene were employed as isotropic solvents and the nematic liquid crystal molecule 4‐cyano‐4 ′ ‐n‐pentyl‐biphenyl, was considered as anisotropic medium. Swelling ratios were calculated by taking into account diameter sizes as function of immersion time compared to the dry state. Experimental data were analyzed using the Komori–Sakamoto approach and the results of this model were found to be in good agreement with the obtained data. The plateau values of the swelling curves at equilibrium were used to establish phase diagrams as function of temperature and solvent concentration. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45452.     

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     

Temperature‐, pH‐, and ion‐stimulus‐responsive swelling behaviors of poly(dimethylaminoethyl methacrylate) gel containing cholic acid

Poly(dimethylaminoethyl methacrylate) hydrogels containing cholic acid (PDMAEMA–CA) were synthesized by radiation crosslinking. The introduction of 10 and 20 mol% cholic acid (CA) into the poly(dimethylaminoethyl methacrylate) (PDMAEMA) hydrogel decreased the maximum swelling ratio (SR) of the gel from 40 to 6 and 5, respectively. The incorporation of CA with dimethylaminoethyl methacrylate led to a decrease in the lower critical swelling temperature of the gel from 44 to 42°C but did not exert big influence on the ion‐stimulus‐responsive properties of the gel. However, the pH sensitivity of the PDMAEMA–CA gel was quite different from that of PDMAEMA gel. The SR of PDMAEMA gel decreased at pH 2.5, whereas the SRs of the PDMAEMA–CA gels showed a convex‐upward function of pH; that is, SR of the PDMAEMA–10% CA gel first increased (pH 1.2–3.2) and then decreased (pH 3.2–11.9) with increasing pH. The pH‐stimulus‐responsive swelling behavior of the PDMAEMA–20% CA gel was similar to that of the PDMAEMA–10% CA gel except for the unique swelling behavior exhibited in the lower pH region. The unique decrease in SR in strong acidic solutions was attributed to aggregations driven by the hydrophobic interactions between CA molecules. Phase separation of the gel in strongly acidic solutions was observed; that is, the margin of the swollen gel was transparent and elastic (cellular structure), whereas the core of it was opaque (aggregated structure) as recorded by scanning electron microscopy. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39998.     

Adsorption of ammonium and nitrate ions by poly(N‐isopropylacrylamide) gel and poly(N‐isopropylacrylamide‐co‐chlorophyllin) gel in different states

The adsorption of ammonium and nitrate by temperature‐stimulus‐responsive poly(N‐isopropylacrylamide) (NIPA) gel and poly(N‐isopropylacrylamide‐co‐chlorophyllin) (NIPA‐CH) gel in different states was investigated. Both the NIPA gel and NIPA‐CH gel could adsorb ammonium and nitrate in a swollen state (swollen gel) and a swelling state (swelling gel), and they adsorbed ammonium more than nitrate. When the gels were shrinking (shrinking gel), they could adsorb a little ammonium from solution, but when the gels were in a shrunken state (shrunken gel), they hardly adsorbed ammonium. The adsorption of both ammonium and nitrate increased for the swelling NIPA gel in comparison with the swollen gel. The NIPA‐CH gel was the opposite in this respect. The difference in the amounts of adsorption of ammonium and nitrate by the swollen and swelling NIPA‐CH gels was more significant than that of the NIPA gels. It was suggested that ions such as ammonium and nitrate could not diffuse into the gels freely. The adsorption of ammonium and nitrate was affected not only by the phase transitions of the gels but also by the electrical charges. The experimental results for the adsorption of ammonium and nitrate during the volume changes of the gels imply that if the gels are applied to the immobilization of microorganisms, they may improve mass transfer between the immobilization matrix and bulk liquid under cyclic temperature changes and promote reactions of the immobilized microorganisms, especially the nitrification of nitrifying bacteria immobilized by the NIPA‐CH gel. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2367–2372, 2005     

Preparation of electrorheological active ionomers from poly(2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine)

In this study, synthesis, characterization, partial hydrolysis, and salt formation of poly(2‐hydroxyethyl methacrylate)‐co‐poly(4‐vinyl pyridine), (poly(HEMA)‐co‐poly‐(4‐VP)) copolymers were investigated. The copolymers were synthesized by free radical polymerization using K₂S₂O₈ as an initiator. By varying the monomer/initiator ratio, chain lengths of the copolymers were changed. The copolymers were characterized by gel permeation chromatography (GPC), viscosity measurements, ¹H and ¹³C NMR and FTIR spectroscopies, elemental analysis, and end group analysis methods. The copolymers were partially hydrolyzed by p‐toluene sulfonic acid monohydrate (PTSA·H₂O) and washed with LiOH_(aq) solution to prepare electrorheological (ER) active ionomers, poly(Li‐HEMA)‐co‐poly(4‐VP). © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3540–3548, 2006     

Preparation and antidehydration of interpenetrating polymer network hydrogels based on 2‐hydroxyethyl methacrylate and N‐vinyl‐2‐pyrrolidone

This work reports the preparation of 2‐hydroxyethyl methacrylate (HEMA)/N‐vinyl‐2‐pyrrolidone (NVP) interpenetrating polymer network (IPN) hydrogels by UV‐initiated polymerization in the presence of free radical photoinitiator Darocur 1173 and cationic photoinitiator 4,4′‐dimethyl diphenyl iodonium hexafluorophosphate. The polymerization mechanism was investigated by the formation of gel network. The structure and morphology of the HEMA/NVP IPN hydrogels were characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that the IPN gels exhibited homogeneous morphology. The dehydration rates of HEMA/NVP IPN hydrogels were examined by the gravimetric method. The results revealed that the hydrogels had a significant improvement of antidehydration ability in comparison with poly(2‐hydroxyethyl methacrylate)(PHEMA) hydrogel embedded physically with poly(N‐vinyl‐2‐pyrrolidone)(PVP). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

pH‐sensitive acrylic‐based copolymeric hydrogels for the controlled release of a pesticide and a micronutrient

Acrylic‐based copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) have been prepared by solution and bulk polymerization techniques using benzoyl peroxide (BPO) as an initiator. Three polymers were prepared with a varying ratio of MMA/MAA. In an effort to increase the hydrophilicity of the matrix, one MMA/MAA polymer was prepared by adding an additional amount of 2‐hydroxy ethyl methacrylate (HEMA). All the polymers were crosslinked in situ by ethylene glycol dimethacrylate (EGDMA). These polymers were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Viscous flow characteristics were determined from solution viscosity and rheological measurements. Dynamic and equilibrium swelling experiments were carried out under varying pH conditions (i.e., 0.1N NaOH, 0.1N HCl, and double‐distilled water). Partially crosslinked hydrogels show varying hydrophilicity because of the presence of carboxylic acid groups making them pH‐responsive. Swelling increased with an increasing number of —COOH groups on the polymer backbone and the hydrophilicity varied with changing pH. Cypermethrin, a widely used pesticide, and cupric sulfate, a model micronutrient, were loaded into these pH‐sensitive hydrogels to investigate their controlled release characteristics. The in vitro release rates of both compounds have been carried out under static dissolution conditions at 30°C. Release data have been fitted to an empirical relation to estimate transport parameters. The release results have been discussed in terms of the varying hydrophilicity of the hydrogel network polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 394–403, 2003     

Colon‐specific oral delivery of vitamin B2 from poly(acrylamide‐co‐maleic acid) hydrogels: An in vitro study

Hydrogels, composed of poly(acrylamide‐co‐maleic acid) were synthesized and the release of vitamin B₂ from these gels was studied as a function of the pH of the external media, the initial amount of the drug loaded, and the crosslinking ratio in the polymer matrix. The gels containing 3.8 mg of the drug per gram gel exhibit almost zero‐order release behavior in the external media of pH 7.4 over the time interval of more than their half‐life period (t_1/2). The amount of the drug loaded into the hydrogel also affected the dynamic release of the encapsulated drug. As expected, the gels showed a complete swelling‐dependent mechanism, which was further supported by the similar morphology of the swelling and release profiles of the drug‐loaded sample. The hydrophilic nature of the drug riboflavin does not contribute toward the zero‐order release dynamics of the hydrogel system. On the other hand, the swelling osmotic pressure developed between the gels and the external phase, due to loading of the drug by equilibration of the gels in the alkaline drug solution, plays an effective role in governing the swelling and release profiles. Finally, the minimum release of the drug in the swelling media of pH 2.0 and the maximum release with zero‐order kinetics in the medium of pH 7.4 suggest that the proposed drug‐delivery devices have a significant potential to be used as an oral drug‐delivery system for colon‐specific delivery along the gastrointestinal (GI) tract. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1133–1145, 2002; DOI 10.1002/app.10402