Synthesis of copolymeric acrylamide/potassium acrylate hydrogels blended with poly(vinyl alcohol): Effect of crosslinking and the amount of poly(vinyl alcohol) on swelling behavior

A novel series of copolymeric acrylamide/potassium acrylate superabsorbents, blended with poly(vinyl alcohol), have been synthesized by using N, N′‐methylenebisacrylamide as a crosslinker and potassium persulphate (K₂S₂O₈) as an initiator. Swelling behavior of these hydrogels in water was investigated; and on the basis of swelling properties, the diffusional behavior of water into these hydrogel systems was analyzed. It was observed that with the increase of amount of poly(vinyl alcohol) or crosslinking, the swelling of the hydrogels decreased. The hydrogel synthesized by addition of 5% poly(vinyl alcohol) and 0.25% crosslinking showed maximum swelling of 54445%. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1927–1931, 2005     

Network characterization and swelling behavior of chemical hydrogels based on acid‐containing poly(vinyl alcohol)

Poly(vinyl alcohol) (PVA) was modified with phthalic and succinic anhydrides to give vinyl alcohol–vinyl ester copolymers that contain carboxylate groups. These half‐esters were then crosslinked by using the poly‐ (ethylene glycol) (PEG) 400 diglycidylether. Low crosslinker/carboxylate ratios were used to obtain low degrees of crosslinking, so the capacity of the resulting hydrogel to absorb water was high. Water absorption was determined gravimetrically as a function of time at room temperature. The equilibrium swelling ratio and compressive modulus were characterized for all the resulting PVA hydrogels and related to the network structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 3026–3031, 2003     

Comparison of the thermal behaviour of aqueous solutions and hydrogels of poly(N-methylol acrylamide)

The intrinsic viscosity ([η]) in water of a sample of linear poly(N-methylol acrylamide) (PMAM) has been measured over the range 278–348 K and the swelling ratio (Q) in water of a sample of chemically crosslinked PMAM has been determined within the interval 278–353 K. The plots of [η] and Q versus temperature (T) both exhibited a maximum. The viscometric behaviour is consistent with an analysis based on excluded volume theory, which indicates the existence of a critical solution temperature both below (263 K) and above (375 K) the maximum. The swelling data were analysed on the basis of the Flory-Rehner theory which yielded a predicted minimum in the dependence of the polymer-water interaction parameter (χ) with T, thus according with the observed maximum in Q versus T. Prolonged heating of linear PMAM and its xerogel yielded products, which were no longer soluble or swellable, respectively, in water. The induced crosslinking proposed as the cause has been confirmed by chemical and infra-red analysis.     

Preparation and swelling behavior of macroporous poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels

Macroporous superabsorbent hydrogels (SAHs) composed of acrylamide (AAm) and sodium methacrylate (NMA) were prepared by aqueous solution polymerization in the presence of a glucose solution. Their swelling capacity was investigated as a function of the concentrations of the glucose solution, sodium methacrylate, crosslinker, initiator, and activator. The porosity of the poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels was confirmed using scanning electron microscopy. The SAHs were characterized by IR spectroscopy. To estimate the effect on the swelling behavior, three types of crosslinkers were employed: N,N′‐methylenebisacrylamide, 1,4‐butanediol diacrylate, and diallyl phthalate. Network structural parameters such as initial swelling rate, swelling rate constant, and maximum equilibrium swelling were evaluated by water absorption measurement. The equilibrium water content (EWC%) of the AAm–NMA macroporous SAHs was found to be in the range of 93.31–99.68, indicating that these SAHs may have applications as biomaterials in the medicinal, pharmaceutical, and veterinary fields. Most of the SAHs prepared in this investigation followed non‐Fickian‐type diffusion, and few followed a case II– or super–case II‐type diffusion. The diffusion coefficients of these macroporous SAHs were investigated. Further, the swelling behavior of these SAHs also was investigated at different pHs and in different salt solutions and simulated biological fluids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3202–3214, 2006     

Network parameters and volume phase transition behavior of poly(N‐isopropylacrylamide) hydrogels

Thermosensitive hydrogels were prepared by free radical polymerization in aqueous solution from N‐isopropylacrylamide (NIPA) monomer and N,N‐methylenebis(acrylamide) (MBAAm) crosslinker. The swelling equilibrium of the hydrogels in deionized water was investigated as a function of temperature and MBAAm content. The results indicated that the swelling behavior and temperature sensitivity of the hydrogels were affected by the amount of MBAAm content. The average molecular mass between crosslinks and polymer–solvent interaction parameter (χ) of the hydrogels were determined from equilibrium swelling values. The swelling variations were explained according to swelling theory based on the hydrogel chemical structure. The swelling equilibrium of the hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In deionized water, the hydrogels showed a discontinuous volume phase transition at 32°C. In SDS and DTAB solutions, the equilibrium swelling ratio and the volume phase transition temperature (lower critical solution temperature) of the hydrogels increased, which is ascribed to the conversion of nonionic PNIPA hydrogel into polyelectrolyte hydrogels because of binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method; it was found that the electric conductivity of the PNIPA–surfactant systems depended strongly on both the type and concentration of surfactant solutions. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1756–1762, 2006     

温敏性聚(N-异丙基丙烯酰胺)/聚丙烯酰胺互穿网络水凝胶

采用紫外引发法制备了物理交联的聚(N-异丙基丙烯酰胺)和化学交联聚丙烯酰胺为组分的互穿网络水凝胶。利用FFIR对所得的凝胶进行了结构分析;测定了该水凝胶在20℃时的溶胀率和50℃时的水保持率;利用DMA和DSC分别研究了水凝胶的储能模量随温度的变化及相转变行为。结果表明:与聚(N-异丙基丙烯酰胺)水凝胶相比,该水凝胶有较好的溶胀率;且具有超快的响应速率,如10 min内失去90%的水;其储能模量增加;虽然其相转变行为变弱,但临界溶解温度(LCST)有所提高。     

Use of superswelling acrylamide/maleic acid hydrogels for monovalent cationic dye adsorption

Acrylamide/maleic acid (AAm/MA) superswelling hydrogels prepared by irradiation with γ radiation were used in experiments on swelling, diffusion, and adsorption of some water‐soluble monovalent cationic dyes such as basic red 5 (BR‐5), basic violet 3 (BV‐3), and brilliant cresyl blue (BCB). The AAm/MA hydrogel containing 60 mg MA and irradiated at 5.20 kGy was used for swelling and diffusion studies in water and aqueous solutions of the monovalent cationic dyes. For this superswelling hydrogel the swelling studies indicated that swelling increased in the following order: BR‐5 > water > BV‐3 ≥ BCB. The diffusion of water and the dyes within the hydrogels was found to have a non‐Fickian character. The uptake of the cationic dyes to the AAm/MA superswelling hydrogels was studied by the batch adsorption technique at 25°C. The uptake of dyes within the hydrogel increased in the following order: BR‐5 > BV‐3 > BCB. In the experiments of the adsorption equilibrium, S‐type adsorption in Giles' classification system was found. The binding ratio of the hydrogel/dye systems was gradually increased with the increase of the MA content in the AAm/MA hydrogel and the irradiation dose. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1809–1815, 2001     

Investigation of pH sensitivity of poly(acrylic acid‐co‐acrylamide) hydrogel

It was found that the upper critical solution temperature (UCST) of poly(acrylic acid‐co‐acrylamide) hydrogel decreases with increase in pH. The UCST of samples equilibrated in a buffer at pH 2.5 was 33.7 °C, whereas it shifted to below 0 °C when swollen in buffers above pH 10. FT‐IR showed that COOH group of acrylic acid ionized gradually in alkaline media. The morphology change of the hydrogel swollen in different buffers was studied by environmental scanning electron microscopy (ESEM). ESEM images showed that the pore size of the sample increased with increase in pH, and in strongly basic media the three‐dimensional network was replaced by a ‘sausage‐like’ or ‘desert‐like’ structure. A study of the pH‐dependent release of cefazolin sodium was also carried out. Copyright © 2003 Society of Chemical Industry     

Synthesis and characterization of novel swelling tunable oligomeric poly(styrene‐co‐acrylamide) modified clays

The oligomeric poly(styrene‐acrylamide‐vinylbenzylchloride) (P(St‐AM‐VBC)) quaternary ammonium salts have been prepared from the reactions of trimethylamine with the corresponding P(St‐AM‐VBC)s, which were synthesized by free‐radical polymerization of a mixture of styrene, acrylamide, and vinylbenzylchloride. Then the swelling tunable oligomeric poly(styrene‐co‐acrylamide) modified clays have been prepared through cation exchange of the sodium ions in the clay with the corresponding P(St‐AM‐VBC) quaternary ammonium salts. The P(St‐AM‐VBC) and its modified clays have been characterized by infrared spectra (IR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), proton nuclear magnetic resonance (¹H NMR), X‐ray diffraction (XRD), and transmission electron microscopy (TEM). The solvent‐swelling capacity of poly(styrene‐co‐acrylamide) modified clays have also been tested, and the experimental results have indicated that these clays are novel swelling tunable organic clays. XRD and TEM studies have shown that these novel swelling tunable clays are well‐intercalated or exfoliated. Furthermore, TGA analysis shows that these polymerically modified clays have high thermal stability for nanocomposites by melt blending. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Swelling and elasticity of hydrogels based on poly(ethylene oxide) macroinimer

A novel method for the preparation of hydrogels based on poly(ethylene oxide) (PEO) is presented. A PEO macroinimer possessing both polymerizable and radical generation sites was used to obtain hydrogels having dangling PEO chains. It was shown that PEO macroinimer acts during photopolymerization, both as a monomer and a crosslinker and thus, leads to the formation of hydrogels of various swelling capacities and moduli of elasticity. Copyright © 2004 Society of Chemical Industry     

Structure‐property and swelling behavior of electron beam irradiated poly(vinyl alcohol)/acrylamide/sodium montmorillonite clay composites

Composites based on poly(vinyl alcohol) (PVA), acrylamide monomer (AM) and sodium montmorillonite clay (MMT) were prepared, in the form of thin films, by solution casting. The PVA/AM/MMT composites films were then exposed to electron beam irradiation to form crosslinked network structure. The structure‐property behavior of PVA/AM/MMT hybrids was demonstrated by x‐ray diffraction (XRD), scanning electron microscopy, gel content, color intensity, thermogravimetric analysis (TGA) and swelling behavior in aqueous solutions. The results indicated that the introduction of MMT clay ratio up to 5% decreased the gel content of PVA/AM hydrogels. The color measurements indicated that the introduction of MMT clay ratio up to 5% was shown to affect the color intensity of composite films. It was found that both PVA/AM hydrogels and PVA/AM/MMT composites reached the equilibrium swelling state in water after four hours; however PVA/AM/MMT composites displayed higher swelling than PVA/AM hydrogels. However, the swelling of PVA/AM hydrogels or their composites at the equilibrium state increased with increasing temperature up to 60°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Swollen behavior of crosslinked network hydrogels based on poly(vinyl alcohol) and polydimethylsiloxane

Poly(vinyl alcohol) (PVA) was dissolved in the water to make a 10 wt % aqueous solution, and polydimethylsiloxane (PDMS) was mixed with 1 wt % 2,2‐dimethyl‐2‐phenylacetophenone (DMPAP) and 0.5 mol % methylenebisacrylamide (MBAAm) in isopropyl alcohol. This mixture was added to a PVA aqueous solution and heated at 90°C for 7 h. Various crosslinked networks were prepared at different molar ratios of PVA/PDMS (1:1, 1:3, and 3:1). The characterization of PVA/PDMS crosslinked networks was determined by Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), a universal testing machine (UTM), and the equilibrium water content (EWC). The DSC melting endotherms showed, at 219.49°C, a sharp endothermic peak of PVA, and PVA/PDMS crosslinked networks had melting peaks close to this point. The value of EWC increased with the content of PVA in the crosslinked networks, simultaneously depending on the temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 957–964, 2002     

Relaxational behavior and swelling‐pH master curves of poly[(diethylaminoethyl methacrylate)‐graft‐(ethylene glycol)] hydrogels

Poly[(diethylaminoethyl methacrylate)‐graft‐(ethylene glycol)] hydrogels were prepared with a molar ratio of 10:1 of diethylaminoethyl methacrylate to poly(ethylene glycol) of number‐average molecular weights (M_n) 200, 400 and 1000 g mol^?1 using tetra(ethylene glycol) dimethacrylate to give a crosslinking ratio between 0.5 and 4.0 %. Glucose oxidase and catalase were immobilized in the matrix during polymerization. The maximum enzyme loading used was 6.6 × 10^?4 g of glucose oxidase per g of polymer. The equilibrium and dynamic swelling properties of these hydrogels were investigated. The pH‐dependent equilibrium swelling characteristics showed a sharp transition between the swollen and the collapsed state at pH 7.0. The dynamic response of the hydrogel discs to pH was analyzed in pulsatile pH conditions. The effects of particle size, crosslinking and molecular weight of poly(ethylene glycol) (PEG) on the dynamic swelling response were investigated. The pulsatile nature of the response was analyzed using Boltzmann superposition. Swelling–pH master curves were obtained. Copyright © 2004 Society of Chemical Industry     

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.     

Discrimination of the roles of crosslinking density and morphology in the swelling behavior of crosslinked polymers: Poly(N‐vinylimidazole) hydrogels

The degree of swelling (S) of crosslinked polymers depends on several variables whose individual contributions are difficult to be distinguished. The aim of this work is to determine the contributions of the morphology to S, discriminating them from the effect of the crosslinking density. Under usual conditions of synthesis, these two characteristics vary simultaneously but here, several samples of chemically crosslinked poly(N‐vinylimidazole) having the same permanent crosslinking density (determined by DSC) and different porous morphologies (determined by SEM) were prepared. It was thus found that the variation of S with porosity, keeping constant the rest of variables, is strongly solvent dependent. Swelling in methanol is almost constant whereas for ethanol, deionized water, and aqueous HCl solutions, S depends on morphological features in a different way for each medium. It was concluded that S increases with inherent porosity and solvent effects arise from the counterbalance of such increment with the dependence of the polymer‐solvent interaction parameter on the polymer volume fraction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Interpolymer complexes of poly(acrylamide) and poly(N-isopropylacrylamide) with poly(acrylic acid): a comparative study

The interpolymer complexation, through successive hydrogen bonding, between poly(acrylamide) (PAAm) and poly(N-isopropylacrylamide) (PNiPAAm) with poly(acrylic acid) (PAA) in aqueous solution has been viscometrically and potentiometrically investigated. The stoichiometry of the complexes formed was determined. By comparing the strength of the two complexes the very important contribution of the hydrophobic interaction in their formation has been indicated.     

Photopolymerization synthesis of poly(N-isopropylacrylamide) hydrogels

Poly(N-isopropylacrylamide) (NIPAAm) gels were formed by photopolymerization of NIPAAm in the absence of a crosslinker using a water solvent at 25°C. Factors affecting formation were the wavelength region of irradiated light, the type of photoinitiators, and the concentrations of the photoinitiator and monomer. A high-pressure mercury lamp (400 W) was used as a light source. An NIPAAm concentration of 10 wt % and irradiation time of 15 h was used for the photopolymerization. The gel (68% yield) was formed when the quartz glass system was used, but no gelation was observed for the Pyrex glass system that transmits light with π > 290 nm. The gel (100% yield) was easily formed, even in the latter system, when 30 mmol/L of hydrogen peroxide and potassium persulfate were used as the photoinitiator. Water soluble photoinitiators such as ferric chloride and sodium anthraquinone-2,7-disulfonate were not effective for the gel formation. Yield of the gel increased with increasing the potassium persulfate concentration (1–30 mmol/L), but it decreased when a high concentration of hydrogen peroxide (60 mmol/L) was used. The gel yield increased with the NIPAAm concentration (5–20 wt %). The degree of swelling of the resultant poly(NIPAAm) gels, which was measured by immersing the gels in water at various temperatures (0–50°C) for 24 h, steeply decreased at about 30°C with increasing temperature, exhibiting a temperature-responsive character. The gels swelled and shrank in water below and above the temperature, respectively. The extent of the character depended on the concentrations of hydrogen peroxide and monomer. The formation mechanism of the gel in the photopolymerization of NIPAAm using hydrogen peroxide photoinitiator was discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1313–1318, 1997     

Drug release behavior of electrical responsive poly(vinyl alcohol)/poly(acrylic acid) IPN hydrogels under an electric stimulus

The electrically modulated properties of interpenetrating polymer networks (IPN) composed of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAAc) under electric field were investigated for drug delivery systems. PVA/PAAc IPNs with various compositions were synthesized by a sequential method, that is, ultraviolet polymerization of AAc in the mixture of PVA and aqueous AAc monomer solution, followed by a freeze‐thawing process to prepare elastic hydrogels. The amount of loaded drug significantly increased with the content of PAAc containing ionizable groups in IPN. The amount of introduced ionic drug (cefazoline) was greater than that of the nonionic drug (theophylline). Release behaviors of drug molecules from negatively charged PVA/PAAc IPN were switched on and off in a pulsatile pattern depending on the applied electric stimulus. The released amount and the release rate of drug were influenced significantly by the applied voltage, ionic group contents in IPN, ionic properties of drug solute, and the ionic strength of release medium. In addition, the ionic properties of drug molecules dramatically affected release behaviors, thus the release of ionic drug was much more enhanced than that of the nonionic drug. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1752–1761, 1999     

Synthesis and superswelling behavior of carboxymethylcellulose–poly(sodium acrylate‐co‐acrylamide) hydrogel

In this paper, attention is paid to synthesis and swelling behavior of a superabsorbent hydrogel based carboxymethylcellulose (CMC) and polyacrylonitrile (PAN). The physical mixture of CMC and PAN was hydrolyzed in NaOH solution to yield hydrogel, CMC–poly(NaAA‐co‐AAm). During alkaline hydrolysis, the nitrile groups of PAN were completely converted to a mixture of hydrophilic carboxamide and carboxylate groups followed by in situ crosslinking of the grafted PAN chains. A proposed mechanism for hydrogel formation was suggested and the structure of the product was established using FTIR spectroscopy. The reaction variables affecting the swelling capacity of the hydrogel were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Swelling measurements of the synthesized hydrogels in various chloride salt solutions indicated a swelling‐loss with increase in the ionic strength of the salt solutions. The pH of the various solutions also affected the swelling of the superabsorbent. Furthermore, the present hydrogels showed a pH‐reversible property. Finally, the swelling kinetics of synthesized hydrogels with various absorbent particle sizes was briefly examined. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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