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     

pH-responsive swelling behavior,elasticity and molecular characteristics of poly(<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylaminoethyl methacrylate) gels at various initial monomer concentrations

The equilibrium swelling degree and the modulus of elasticity of pH-responsive poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) gels prepared at various initial monomer concentrations were investigated both in buffer solutions and in aqueous salt solutions. As pH of the solution is increased, PDMAEMA gels first remain in the swollen state up to pH 7.7, then exhibit pH-sensitive phase transitions at 8.0 in which PDMAEMA gels attain a collapsed state. The swelling kinetic measurements of PDMAEMA gels showed that pH sensitivity of PDMAEMA is quite stable and the swelling process is reproducible in accordance with pH changing. The swelling behavior of PDMAEMA gels was analyzed by Flory-Rehner theory and the results were combined by the results of compression measurements to calculate the molecular characteristics of gels. The resulting pH-responsive PDMAEMA gels were elastic and displayed good swelling behavior both in buffer solutions and in aqueous salt solutions, therefore, they can be used as a kind of carrying material in drug delivery systems.     

Collapse of acrylamide‐based polyampholyte hydrogels in water

The swelling behavior of balanced acrylamide (AAm)‐based polyampholyte hydrogels in water and in aqueous salt (NaCl) solutions was investigated. Equimolar ratio of the ionic comonomers 4‐vinylpyridine (cationic monomer) and acrylic acid (anionic monomer) were used together with the nonionic monomer AAm in the hydrogel preparation. The variations of the hydrogel volume in response to changes in pH were measured. It was found that the hydrogels are in a collapsed state not only at the pH of the isoelectric point pH_IEP but also over a wide range of pH including pH_IEP. The width of the collapsed plateau increased and the hydrogels assumed a more compact state as the ionic group content is increased. The antipolyelectrolyte behavior was observed along the collapsed plateau region, where the gel occupies a larger volume in salt solution. The experimental swelling data were compared with the predictions of the Flory‐Rehner theory of swelling equilibrium including the ideal Donnan equilibria. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermoreversible hydrogels X: Synthesis and swelling behavior of the (N‐isopropylacrylamide‐co‐sodium 2‐acrylamido‐2‐methylpropyl sulfonate) copolymeric hydrogels

A series of thermosensitive hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm) and sodium‐2‐acrylamido‐2‐methylpropyl sulfonate (NaAMPS). Factors such as temperature and initial total monomer concentration and different pH solutions were investigated. Results indicated that the more the NaAMPS content in hydrogel system, the higher the swelling ratio and the gel transition temperature; the higher the initial monomer concentration, the lower the swelling ratio. The result also indicated that the NIPAAm/NaAMPS copolymeric hydrogels had different swelling ratios in various pH environments. The present gels showed a pH‐reversible property between pH 3 and pH 10 and thermoreversibility. The swelling ratios of copolymeric gels were lower in a strong alkaline environment because the gels were screened by counterions. Finally, the drug release behavior of these gels was also investigated in this article. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1760–1768, 2000     

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     

温度及pH敏感生物水凝胶的研究

运用互穿网络技术,合成了具有温敏性的聚(N 异丙基丙烯酰胺)(PNIPAm)和生物大分子明胶(gelatin)的互穿网络聚合物(PNIPAm/Gelatinsemi IPN和PNIPAm/GelatinIPN)水凝胶,该水凝胶的最低临界溶液温度(LCST)与PNIPAm水凝胶的LCST基本相同,均为33℃左右,但在LCST以下的平衡溶胀率减小、相变区域略微变宽。在此基础上,通过N 异丙基丙烯酰胺(NIPAm)与丙烯酸(AAc)交联共聚,改变了水凝胶的LCST,在pH=4 0的缓冲溶液中,各水凝胶的溶胀行为基本一致,与AAc含量无关,LCST都为28℃左右;在pH>4 0的缓冲溶液中,LCST随AAc组分含量的增加而增加,但温敏性减小。同时,AAc的加入,使水凝胶具有pH敏感性,敏感点为pH=4 5左右。还考察了该水凝胶降解的特点:戊二醛(GA)交联后的明胶网络,保留了明胶的生物降解性,但互穿网络水凝胶在实验条件下几乎未被胃蛋白酶和胰蛋白酶降解,在pH=9 6的碱性条件下,水凝胶可发生化学降解。     

Interpenetrating polymeric network hydrogels for potential gastrointestinal drug release

New interpenetrating polymeric network (IPN) hydrogels based on chitosan (C), poly(N‐vinyl pyrrolidone) (PVP) and poly(acrylic acid) (PAAc), crosslinked with glutaraldehyde (G) and N,N‘‐methylenebisacrylamide (MBA), were prepared and investigated for potential gastrointestinal drug delivery vehicles utilizing a model drug, amoxicillin. IPN hydrogels were synthesized by simultaneous polymerization/crosslinking of acrylic acid monomer in the presence of another polymer (C) and crosslinker (G, MBA). Three different concentrations of glutaraldehyde were used (0.5, 1.0 and 2.0 w/w) to control the overall porosity of the hydrogels, named C‐P‐AAc/0.5, C‐P‐AAc/1.0 and C‐P‐AAc/2.0, respectively. Spectroscopic and thermal analyses such as Fourier transform infrared spectroscopy, thermogravimetric analysis and thermomechanical analysis were performed for IPN characterization. Equilibrium swelling studies were conducted for pH and temperature response behavior. Swelling studies were also carried out in simulated gastric fluid of pH = 1.1 and simulated intestinal fluid of pH = 7.4 to investigate possible site‐specific drug delivery. It was found that the release behavior of the drug from these IPN hydrogels was dependent on the pH of the medium and the proportion of crosslinker in the IPN. It was observed that amoxicillin release at pH = 7.4 was higher than at pH = 1.1. The analysis of the drug release showed that amoxicillin was released from these hydrogels through a non‐Fickian diffusion mechanism. Copyright © 2007 Society of Chemical Industry     

Swelling behavior of radiation‐polymerized polyampholytic two‐component gels: Dynamic and equilibrium swelling kinetics

Polyampholytic hydrogels, with varying degrees of crosslinking and ionic content, were prepared by radiation polymerization of p‐sodium styrene sulfonate (SSS) and vinyl benzyl trimethylammoniumchloride (VBT). These gels were investigated for their dynamic and equilibrium swelling kinetics. Dynamic swelling of these gels established that the gels containing equal amounts of SSS and VBT strictly follow Fickian diffusion. The hydrogels containing excess of SSS followed the case II type of diffusion, whereas those containing excess of VBT followed anomalous diffusion. Equilibrium swelling kinetics of these gels in aqueous system, ethanol–water mixture, at different pHs, and in the presence of solutions of biological interest was studied. It was seen that gels containing equal amounts of SSS and VBT show the lowest equilibrium swelling. Swelling of the polyampholytic gel decreased with an increase in the radiation dose imparted and the amount of crosslinking agent incorporated in the gel. The gels having an excess of VBT showed higher equilibrium swelling in comparison to those having an excess of SSS. Differential scanning calorimetry (DSC) studies showed that crosslinking of the gels decreases equilibrium swelling but increases the bonded nonfreezable water content of the gels. The organic solvents like ethanol cause abrupt collapse of the polyampholyte gels containing excess of SSS and those containing equal amounts of both the monomers at some critical ratio of water and ethanol in swelling medium. However, the deswelling in the water–ethanol mixture was gradual for gels containing an excess of VBT and the extent of deswelling was also low for these gels in comparison to other gels. The swelled gels of all compositions deswelled when they were transferred to solutions at pH in the range 2–12. Biologically important solutes like urea, glucose, and surfactants like Triton‐X tend to further swell the polymer matrices, whereas NaCl causes their deswelling. The additive effect is more prominent for polyampholyte gels containing excess of either of the monomers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 730–742, 2003     

Whey protein concentrate hydrogels as bioactive carriers

Two sets of heat‐induced hydrogels were prepared from whey protein concentrate (WPC), one set at a constant concentration [15% (w/v)] and varying pHs (pH 5.1–10.0) and the other set at a constant pH (10.0) and varying concentrations (12%, 15%, and 18%). At a given pH, the higher the protein concentration, the shorter was the gelation time and the larger were the equilibrium storage modulus (G) and failure stress. For a given protein concentration, the gelation kinetics and mechanical properties of WPC hydrogels were strongly pH dependent. The swelling behavior of WPC gels was studied at 37.5°C ± 0.5°C. The equilibrium swelling ratio (SR) was at the minimum when pH of the swelling medium was close to the isoelectric point (pI) of the whey protein, and when the swelling medium pH was far from the pI (from 6.0 to 10.0), the SR increased. In particular, when the pH was higher than the pI, the swelling was highly pH sensitive. The higher the WPC concentration used in preparing the hydrogel, the lower was the SR. The controlled drug release properties of the WPC hydrogels were studied using caffeine as the model drug. Consistent with the swelling behavior of the gels, release was slower when the pH of the medium was lower (pH 1.8) than when it was higher (pH 7.5). The SR and the drug release rate decreased significantly when the gels were surface‐coated with alginate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

pH–thermoreversible hydrogels. II. Synthesis and swelling behaviors of N-isopropylacrylamide-co-acrylic acid-co-sodium acrylate hydrogels

A series of pH–thermoreversible hydrogels are prepared from the three molar ratios of N-isopropylacrylamide (NIPAAm) and acrylic acid neutralized 50 mol % by sodium hydroxide (SA50) and N,N′-methylene bisacrylamide (NMBA). The influence of the environmental conditions, such as temperature and pH values, on the swelling behavior of these copolymeric gels is also investigated in this article. Results show that the hydrogels bearing negative charges exhibit different equilibrium swelling ratios under various pH media. The pH sensitivities of these gels also strongly depend on the molar ratio of SA50 in the copolymeric gels; thus, the more the SA50 content, the higher the gel pH sensitivity. These hydrogels exhibited thermosensitivity demonstrating a larger change of the equilibrium swelling ratio in aqueous media under temperature changes. An overshooting phenomenon is observed from the gel swelling kinetics under high-temperature conditions. The said hydrogels are also used to investigate the release of model drugs in this study. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1955–1967, 1999     

Synthesis and characterization of pH- and thermoresponsive Poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-itaconic acid) hydrogels crosslinked with <Emphasis Type="Italic">N</Emphasis>-maleyl chitosan

Biodegradable cross-linker N-maleyl chitosan (N-MACH) was synthesized with chitosan (CS) and maleic anhydride (MA) by acylation. With N-MACH cross-linker, a series of cross-linked poly(N-isopropylacrylamide-co-itaconic acid) [P(NIPAAm-co-IA)] hydrogels were prepared, and their pH-and temperature-responsive behaviors, water contents, swelling/deswelling kinetics were investigated. By alternating the NIPAAm/IA weight ratios, hydrogels had the volume phase transition temperature (VPTT) changed from 33 to 38 °C, whereas cross-linking density did not affect the VPTT apparently. The water content of hydrogels was controlled by the monomer weight ratios of NIPAAm/IA, swelling media, and the cross-linking density. The results of the influence of pH value on the swelling behaviors showed that the minimum swelling ratios of the hydrogels appeared in neutral buffer solution, which was attributed to chemical composition of the hydrogels and the swelling media. In the swelling/deswelling kinetics, all the dried hydrogels exhibited fast swelling within 480 min and fast deswelling within 20 min, which was independent of the content of IA and cross-linker.     

Radiation synthesis and characterization of poly(N‐vinyl‐2‐pyrrolidone/acrylic acid) and poly(N‐vinyl‐2‐pyrrolidone/acrylamide) hydrogels for some metal‐ion separation

Two different hydrogels, prepared from N‐vinyl‐2‐pyrrolidone/acrylic acid (NVP/AAc) and N‐vinyl‐2‐pyrrolidone/acrylamide (NVP/AAm), were studied for the separation and extraction of some heavy‐metal ions from wastewater. The hydrogels were prepared by the γ‐radiation‐induced copolymerization of the aforementioned binary monomer mixtures. Further modification was carried out for the NVP/AAc copolymer through an alkaline treatment to improve the swelling behavior by the conversion of the carboxylic acid groups into its sodium salts. The thermal stability and swelling properties were also investigated as functions of the N‐vinyl‐2‐pyrrolidone content. The characterization and some selected properties of the prepared hydrogels were studied, and the possibility of their practical use in wastewater treatment for heavy metals such as Cu, Ni, Co, and Cr was investigated. The maximum uptake for a given metal was higher for a treated NVP/AAc hydrogel than for an untreated NVP/AAc hydrogel and was higher for an untreated NVP/AAc hydrogel than for an NVP/AAm hydrogel. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2642–2652, 2004     

Synthesis and Characterization of Temperature-Sensitive Poly(N-isopropylacryamide) Hydrogel with Comonomer and Semi-IPN material

A series of temperature and pH sensitive hydrogels were synthesized using N-isopropylacrylamide (NIPAAm) as main monomer, sodium alginate (SA) as semi-IPN material, ethyl acrylate (EA) and acrylic acid (AA) as comonomer, and N-maleyl chitosan (N-MACH) as cross-linker. The temperature and pH sensitive behavior, swelling/deswelling kinetics of the hydrogels were investigated. And the mechanism of the phase transition was summed up. Sodium alginate/Poly(N-isopropylacryamide) semi-interpenetrating polymer network (SA/PNIPAAm semi-IPN) hydrogels exhibited a lower critical solution temperature (LCST) at about 32 °C with no significant deviation from the conventional PNIPAAm hydrogels. Poly(N-isopropylacryamide-co-ethyl acrylate) (P(NIPAAm-co-EA)) hydrogels exhibited LCST at 29–31°C, increasing the amount of EA in the hydrogel gradually decreased the LCST. Poly(N-isopropylacryamide-co-acrylic acid) [P(NIPAAm-co-AA)] hydrogels exhibited LCST at 34–39°C, with decreasing NIPAAm/AA from 96/4 to 92/8 and 90/10, the LCST increased from 34°C to 37°C and 39°C. In the swelling/deswelling kinetics, all the dried hydrogels exhibited fast swelling/deswelling behavior, which might be attributed to macroporous structures of the hydrogels.     

Fast pH‐thermo‐responsive copolymer hydrogels with micro‐porous structures

Micro‐porous copolymer hydrogels were prepared by γ‐ray irradiation of mixed solutions of N‐isopropylacrylamide (NIPAAm) and acrylic acid (AAc) above the lower critical solution temperature (LCST). From Cryo‐SEM observations, the gels were found to consist of three‐dimensional fibrous micro‐gels and micro‐pores. The copolymer gels swelled at temperatures below the LCST and shrunk at temperatures above it, and they showed rapid volume transitions on a time scale on the order of a minute when experiencing temperature changes between 10 and 40°C. The transition times for thermal shrinking were almost the same regardless of AAc composition, but the transition times for thermal swelling were increased with increasing AAc contents. The copolymer gels also showed rapid volume transitions with time constants on the order of an hour on experiencing pH changes between 2 and 12. The transition times for pH volume change at 10°C were within one hour, except for the gels containing only small amounts of AAc. On the other hand, the transition times for pH‐dependent volume change at 40°C were increased with increasing AAc content. The lower responsiveness of the transition results from an increase in hydrophobicity arising from the formation of inter‐ and intra‐molecular hydrogen bonds between the non‐ionized carboxylic acid groups and the amide groups. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 75–84, 2003     

Preparation and Swelling Study of a pH-Dependent Interpolymeric Hydrogel Based on Chitosan for Controlled Drug Release

Novel pH-dependent, biodegradable interpolymeric network (IPN) hydrogels were prepared for controlled drug release investigations. The IPN hydrogels were prepared by irradiation of solutions of N-acryloyglycine (NAGly), polyethylene glycol diacrylate (PEGDA) mixed with chitosan, in the presence of a lower amount of glutaraldehyde as the crosslinker and using 2,2-dimethoxy-2-phenyl acetophenone as the photo-initiator. The equilibrium swelling studies were carried out for the gels at 37°C in buffer solutions of pH 2.1 and 7.4 (simulated gastric and intestinal fluids, respectively). 5-Fluorouracil (5-FU) was entrapped, as a model therapeutic agent, in the hydrogels and equilibrium-swelling studies were carried out for the drug-entrapped gels at 37°C. The in-vitro release profiles of the drug were established at 37°C in pH 2.1 and 7.4.     

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

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

Photopolymerised thermo-responsive poly(N,N-diethylacrylamide)-based copolymer hydrogels for potential drug delivery applications

Novel thermo-sensitive N,N-diethylacrylamide (DEAAm) based copolymer hydrogels were prepared via UV-induced free radical bulk polymerisation. UV polymerisation was employed to avoid the use of potentially toxic solvents; solution polymerisation has been the most common means for the preparation of PDEAAm-based hydrogels in the literature to date. The resultant hydrogels were analysed using nuclear magnetic resonance, Fourier transform infrared spectroscopy and modulated differential scanning calorimetry. Parameters such as the crosslinking degree and the nature of the incorporated hydrophilic component, N-vinyl-2-pyrrolidone (NVP) or N,N-dimethylacrylamide (DMAAm) were found to impact hydrogel structure, mechanical properties and swelling kinetics. Pulsatile swelling studies indicated that the hydrogels had thermo-reversible properties which were greatly affected by test temperature, nature of hydrophilic monomer used and crosslinker content. Aminophylline was selected as a model solute for drug loading and release studies by thermal deswelling in HCl buffer (pH 1.4) and phosphate buffer media (pH 6.8). The observed lag time prior to significant drug release from the more crosslinked P(DEAAm-NVP) hydrogels could make them suitable for delayed specific release in the intestine and potential alternatives to layers or membranes in time-specific and site-specific swelling-controlled drug delivery systems.     

Thermoreversible hydrogel. V. Synthesis and swelling behavior of the N-isopropylacrylamide-co-trimethyl methacryloyloxyethyl ammonium iodide copolymeric hydrogels

A series of N-isopropylacrylamide/trimethyl methacryloyloxyethyl ammonium iodide (NIPAAm/TMMAI) copolymeric gels are prepared from the various molar ratios of NIPAAm, cationic monomer TMMAI, and N,N′-methylene bisacrylamide (NMBA) in this article. The influences of the amount of the cationic monomer in the copolymeric gels on the swelling behavior in water, various saline solutions, and various temperatures are investigated. Results show that the swelling ratios of copolymeric gels are significantly larger than those of pure homopolymer NIPAAm gel, and the more the TMMAI content, the higher the gel transition temperature. In the saline solution, results show that the swelling ratio of pure NIPAAm gel has not significantly changed with an increase of the salt concentration until the salt concentration is larger than 0.1M. The swelling ratios for the copolymeric gels NIPAAm/TMMAI decrease with increasing salt concentration. In various saline solutions, results show that the anionic effects are greater than cationic effects in the presence of common anion, different cations and common cation, and different anions for these hydrogels. Finally, we also tested the reversibility of the NIPAAm/TMMAI copolymeric gels. The deswelling and reswelling kinetics are dependent on the temperature, which is below or above the gel transition temperature. The gel with little TMMAI content has a good reversibility. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1793–1803, 1998     

Synthesis and characterization of hydrogels based on gamma irradiation of acrylic acid and methacrylic acid

In this work, hydrogels based on different ratios of acrylic acid (AAc) and methacrylic acid (MAc) monomers were prepared by gamma radiation copolymerization. The hydrogels were characterized by IR spectroscopy and thermogravimetric analysis (TGA). The effect of temperature and pH on the degree of swelling of AAc/MAc hydrogels was also studied. The results showed that the gel fraction of AAc is relatively higher than MAc, while the gel fraction of AAc/MAc hydrogels decreased slightly with increasing the ratio of MAc monomer in the initial solution. The IR spectroscopic analysis indicates the formation of copolymer networks and the presence of hydrogen bonding. The thermal study showed that PAAc hydrogel displayed higher thermal stability than PMAc and AAc/MAc hydrogels, over the studied compositions. The results showed that PAAc hydrogel reached equilibrium swelling state in water after 4 h, whereas PMAc and AAc/MAc hydrogels reached the equilibrium after 7 h. In this regard, AAc/MAc hydrogels showed degree of swelling in water lower than PAAc and higher than PMAc hydrogels. It was found that the swelling of the hydrogels based on AAc and MAc monomers or their copolymers increases with increasing temperature up to 50°C. Moreover, it was observed that the degree of swelling of hydrogels were not affected by increasing the pH values up to 4 and increased greatly within the pH values from 5 to 9. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Adsorption of Bovine Serum Albumine Onto Poly (<Emphasis Type="Italic">N</Emphasis>-<Emphasis Type="Italic">t</Emphasis>-Butylacrylamide-co-Acrylamide/Maleic Acid) Hydrogels

In the present study, a series of ionic poly(N-t-butylacrylamide-co-acrylamide) [P(NTBA-co-AAm)] hydrogels were synthesized by free-radical crosslinking copolymerization of N-t-butylacrylamide (NTBA) and acrylamide (AAm) monomers in fixed amount, but changing amount of maleic acid (MA) comonomer in methanol using N,N-methylene-bis-acrylamide (BAAm) as the crosslinker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylethylenediamine (TEMED) as the activator. The swelling behavior of these hydrogels was analyzed in buffer solutions at various pHs. The prepared hydrogels also were investigated swelling-deswelling transition in water depending on the temperature. For the bovine serum albumin (BSA) adsorption, the effect of pH, temperature, initial protein concentration and adsorption rate were investigated. Maximum BSA adsorption was observed at pH 5.0 which is close to the isoelectric pH of BSA (pH 4.8). The highest adsorption rate was achieved in about 12 h. and also, maximum BSA adsorption was found at +5°C.