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

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

Effect of silane coupling agent on swelling behaviors and mechanical properties of thermosensitive hybrid gels

A series of organic–inorganic hybrid thermosensitive gels with three different structures were prepared from N‐isopropylacrylamide (NIPAAm), and N, N′‐methylenebisacrylamide (NMBA) and tetraethoxysilane (TEOS) [N‐IPN]; NIPAAm, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and TEOS [NT‐IPN]; and NIPAAm, TMSPMA, and TEOS [NT‐semi‐IPN] by emulsion polymerization and sol–gel reaction in this study. The effect of different gel structures and coupling agent on the swelling behavior, mechanical properties, and morphologies of the present gels was investigated. Results showed that the properties of the gels would be affected by the gel networks such as IPN or semi‐IPN and with or without existence of TMSPMA as the bridge chain between networks. The NT‐semi‐IPN gel had higher swelling ratio and faster diffusion rate because poly(NIPAAm) moiety in the semi‐IPN gels was not restricted by NMBA network. However, the IPN gels such as N‐IPN and NT‐IPN had good mechanical properties and lower swelling ratio, but had a poor thermosensitivity due to the addition of coupling agent, TMSPMA, into the gel system that resulted in denser link between organic and inorganic components. The morphology showed that IPN gels had partial aggregation (siloxane domain) and showed some denser phases. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effects of TEOS contents on swelling behaviors and mechanical properties of thermosensitive hybrid gels

A series of organic‐inorganic hybrid thermosensitive gels with three different structures and different contents of tetraethoxysilane (TEOS) were prepared from N‐isopropylacrylamide (NIPAAm), and N,N′‐methylene‐bis‐acrylamide (NMBA) and TEOS [N‐IPN]; NIPAAm, 3‐(trimethoxysilyl) propyl methacrylate (TMSPMA) as coupling agent and TEOS [NT‐IPN]; and NIPAAm, TMSPMA and TEOS [NT‐semi‐IPN] by emulsion polymerization and sol‐gel reaction in this study. The effect of TEOS content on the swelling behavior, mechanical properties, and morphologies of the present gels was investigated. Results showed that the properties of the gels would be affected by the gel networks such as IPN or semi‐IPN, existence of TMSPMA as the bridge chain between networks, and content of TEOS. The NT‐semi‐IPN gel had higher swelling ratio because poly (NIPAAm) moiety in the semi‐IPN gels was not restricted by NMBA network. However, the IPN gels such as N‐IPN and NT‐IPN had good mechanical properties and lower swelling ratio, but had bad thermosensitivity due to the addition of coupling agent, TMSPMA, into the gel system that resulted in denser link between organic and inorganic components. Increasing TEOS content would also reduce the thermosensitivity of the hybrid gels. The morphology showed that IPN gels had partial aggregation (siloxane domain) and showed some denser phases. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Behavior of semi IPN hydrogels composed of PEG and AAm/SMA copolymers in swelling and uptake of Janus Green B from aqueous solutions

Semi-interpenetrating polymer network (semi IPN) hydrogels of poly(ethylene glycol; PEG) were prepared as a water adsorbent for dye (Janus Green B) sorption. For this, PEG and copolymer of acrylamide/sodium methacrylate (AAm/SMA) were prepared by polymerization of aqueous solution of acrylamide (AAm), sodium methacrylate (SMA) using ammonium persulfate (APS)/N,N,N′,N′-tetramethylethylenediamine (TEMED) as redox initiating pair in presence of PEG and poly(ethylene glycol)dimethacrylate (PEGDMA) as crosslinker. FTIR spectroscopy was used to identify the presence of different repeating units in the semi IPNs. Some swelling and diffusion characteristics were calculated for different semi IPNs and hydrogels prepared under various formulations. Water uptake and dye sorption properties of AAm/SMA hydrogels and AAm/SMA/PEG semi IPNs were investigated as a function of chemical composition of the hydrogels. Janus Green B have used in sorption studies. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

Synthesis and properties of silver nanoparticles in chitosan‐based thermosensitive semi‐interpenetrating hydrogels

In this article, thermosensitive poly(N‐isopropyl acrylamide‐co‐vinyl pyrrolidone)/chitosan [P(NIPAM‐co‐NVP)/CS] semi‐interpenetrating (semi‐IPN) hydrogels were prepared by redox‐polymerization using N,N‐methylenebisacrylamide as crosslinker and ammonium persulfate/N,N,N′,N′‐tetramethylethylenediamine as initiator. Highly stable and uniformly distributed Ag nanoparticles were prepared by using the semihydrogel networks as templates via in situ reduction of silver nitrate in the presence of sodium borohydride as a reducing agent. Introduction of CS improves the hydrogels swelling ratio (SR) and stabilizes the formed Ag nanoparticles in networks. Scanning electron microscopy and transmission electron microscopy revealed that Ag nanoparticles were well dispersed with diameters of 10 nm. The semi‐IPN hydrogel/Ag composites had higher SR and thermal stability than its corresponding semi‐IPN hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

p(AAm/TA)‐based IPN hydrogel films with antimicrobial and antioxidant properties for biomedical applications

Interpenetrating polymer networks (IPN), either semi‐IPN (s‐IPN) or full IPN, based on a natural polymer tannic acid (TA) and synthetic poly(acrylamide) (p(AAm)) were prepared by incorporation of TA during p(AAm) hydrogel film preparation with and without crosslinking of TA simultaneously. The synthesis of p(AAm/TA) s‐IPN and IPN hydrogels with different amounts of TA were prepared by concurrent use of redox polymerization and epoxy crosslinking. The p(AAm)‐based hydrogels were completely degraded at 37.5°C within 9 and 2 days at pHs 7.4 and 9, respectively. Biocompatibility of p(AAm), s‐IPN, and IPN were tested with WST assay and double staining, they had 75% cell viability up to almost 20 μg mL^?1 concentration against L929 fibroblast cell. Antioxidant properties of IPN and s‐IPN hydrogels were investigated with FC and ABTS^? methods. Antimicrobial properties of TA‐containing s‐IPN, and IPN hydrogels were determined against three common bacterial strains, Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538, and Bacillus subtilis ATCC 6633, and it was found that p(AAm/TA)‐based s‐IPN and IPN hydrogels are effective antimicrobial and antioxidant materials. Moreover, almost up to day‐long linear TA release profiles were obtained from IPN and s‐IPN hydrogels in phosphate buffer solution at pH 7.4 at 37.5°C. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41876.     

Studies on drying and swelling of PAAm‐NIPA composites in various compositions

The steady‐state fluorescence technique was introduced for studying the drying and swelling of disc‐shaped PAAm‐NIPA composites. Disc‐shaped gels were formed with various acrylamides (AAm) and N‐isopropylacrylamides (NIPA) by free radical crosslinking copolymerization in water. Composites were prepared with pyranine (Py) doped as a fluorescence probe. Scattered light, I_sc, and fluorescence intensities, I, were monitored during drying of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time increased respectively for all samples. The Stern‐Volmer equation combined with moving boundary and Li‐Tanaka models were used to explain the behavior of I during drying and swelling, respectively. It was found that the desorption coefficient, D, increased as NIPA contents were increased for a given temperature during drying. However, the cooperative diffusion coefficient, D₀, increased as NIPA contents were decreased during swelling at a given temperature. Supporting gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm‐NIPA composites. It was observed that NIPA contents affect the drying and swelling process. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006     

Environmentally sensitive hydrogels: N‐isopropyl acrylamide/Acrylamide/ Mono‐, Di‐, Tricarboxylic acid crosslinked polymers

Environmentally sensitive hydrogels responsive to various stimuli such as temperature, pH, ionic strength of the medium and the solvent were prepared by using N‐isopropyl acrylamide (NIPAM), acrylamide (AAm) and monomers that have various number of carboxylic acid (XA) functionality using N,N′‐methylene bisacrylamide (Bis) as crosslinker. Hydrogels were prepared via free radical polymerization reaction in aqueous solution. P(NIPAAm‐co‐AAm) and p(NIPAAm‐co‐AAm)/XA hydrogels that contain monoprotic crotonic acid (CA) exhibit a lover critical solution temperature (LCST) at 28°C, whereas p(NIPAAm‐co‐AAm)/IA (IA:itaconic acid), and P(NIPAAm‐co‐AAm)/ACA (ACA:acotonic acid) hydrogels exhibit a lover critical solution temperature at 30.7°C and 34.4°C, respectively. Spectroscopic and thermal analyses were performed for the structural and thermal characterizations of the prepared hydrogel. The swelling experiments as equilibrium swelling percentages by gravimetrically were carried out in different solvents, at different solutions temperature, pH, and ionic strengths to determine their effects on swelling characteristic of hydrogels. POLYM. ENG. SCI., 55:843–851, 2015. © 2014 Society of Plastics Engineers     

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     

Preparation and Swelling Properties of Temperature‐Sensitive Semi‐Interpenetrating Polymer Networks Composed of Poly[(N‐tert‐butylacrylamide)‐co‐acrylamide] and Hydroxypropyl Cellulose

Summary: Temperature‐responsive hydrogels based on linear HPC and crosslinked P(NTBA‐co‐AAm) were prepared by the semi‐IPN technique. The structure of these semi‐IPN hydrogels was investigated by FT‐IR spectroscopy. An increase in normalized band ratios (A₂₉₈₀/A₁₆₆₅) was observed with increasing HPC content in the initial mixture. The swelling kinetics and water transport mechanism of these semi‐IPN hydrogels were examined and their temperature responsive behaviors were also investigated by measuring equilibrium swelling ratios and pulsatile swelling experiments. The results showed that these semi‐IPN hydrogels underwent a volume phase transition between 18 and 22 °C irrespective of the amounts of MBAAm and HPC. However, below the volume phase transition temperature, their equilibrium swelling ratios were affected by the amount of MBAAm and HPC. The pulsatile swelling experiments indicated that the lower the MBAAm and the higher HPC contents in semi‐IPN hydrogels the faster the response rate temperature change.

Equilibrium swelling ratios of the semi‐IPN P(NTBA‐co‐AAm)/HPC hydrogels in water shown as a function of temperature.     

Synthesis of full and semi Interpenetrating hydrogel from polyvinyl alcohol and poly (acrylic acid‐co‐hydroxyethylmethacrylate) copolymer: Study of swelling behavior,network parameters,and dye uptake properties

Semi and full interpenetrating network (IPN) hydrogels were synthesized by allowing free radical copolymerization of acrylic acid (AA) and hydroxyethyl methacrylate (HEMA) in the matrix of polyvinyl alcohol (PVOH). Accordingly, four different semi IPN hydrogels were prepared with PVOH: copolymer mass ratio of 1 : 1, 1 : 0.75, 1 : 0.5, and 1 : 0.25. These hydrogels were designated as SEMIIPN1, SEMIIPN2, SEMIIPN3, and SEMIIPN4, respectively. In all of these SEMIIPN, after polymerization PVOH was crosslinked with 2 mass % glutaraldehyde to form the semi IPN structure. In a similar way, sequential full IPN were prepared from PVOH and copolymer of AA and HEMA (designated as PAAHEMA) with same composition except in this case apart from crosslinking of PVOH by 2 mass % glutaraldehyde the PAAHEMA copolymer was further crosslinked with N,N′‐methylenebisacrylamide (NMBA) to produce four full IPN hydrogels designated as FULLIPN1, FULLIPN2, FULLIPN3, and FULLIPN4. All of these semi and full IPN type hydrogels were characterized by carboxylic %, FTIR, UV, DTA‐TGA, XRD, SEM, and mechanical properties. The network parameters, swelling and diffusion characteristics of these hydrogels were also studied. The performance of these semi and full IPNs were compared in terms of their relative abilities for removing varied concentration of rhodamine B (RB) and methyl Violet (MV) dyes from water. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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     

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     

Thermo‐ and pH‐responsive behaviors of graft copolymer and blend based on chitosan and N‐isopropylacrylamide

Thermo‐ and pH‐sensitive polymers were prepared by graft polymerization or blending of chitosan and poly(N‐isopropylacrylamide) (PNIPAAm). The graft copolymer and blend were characterized by Fourier transform‐infrared, thermogravimetric analysis, X‐ray diffraction measurements, and solubility test. The maximum grafting (%) of chitosan‐g‐(N‐isopropylacrylamide) (NIPAAm) was obtained at the 0.5 M NIPAAm monomer concentration, 2 × 10⁻³ M of ceric ammonium nitrate initiator and 2 h of reaction time at 25°C. The percentage of grafting (%) and the efficiency of grafting (%) gradually increased with the concentration of NIPAAm up to 0.5 M, and then decreased at above 0.5 M NIPAAm concentration due to the increase in the homopolymerization of NIPAAm. Both crosslinked chitosan‐g‐NIPAAm and chitosan/PNIPAAm blend reached an equilibrium state within 30 min. The equilibrium water content of all IPN samples dropped sharply at pH > 6 and temperature > 30°C. In the buffer solutions of various pH and temperature, the chitosan/PNIPAAm blend IPN has a somewhat higher swelling than that of the chitosan‐g‐NIPAAm IPN. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1381–1391, 2000     

Porous silicone hydrogel interpenetrating polymer networks prepared using a template method for biomedical use

Porous interpenetrating polymer networks (IPNs) of polydimethylsiloxane with hydrophilic components synthesized by radical homopolymerization and copolymerization of 2‐hydroxyethyl methacrylate (HEMA) and N,N‐dimethylacrylamide (DMAA) were obtained using a template method. Surface modification of CaCO₃ microsphere templates improved their dispersibility, leading to the realization of IPN films with an interconnected porous structure. Results showed that these porous IPN films exhibited higher swelling abilities, and thus better drug loading capabilities than the corresponding non‐porous films. In addition, IPNs comprised of DMAA exhibited higher swelling abilities and faster drug release rates than those of only HEMA. These silicone hydrogels were also tested for their cytotoxicity against L929 cells, confirming their non‐toxicity to cells and their potential use as materials for biomedical applications. Copyright © 2011 Society of Chemical Industry     

Delivery of bupivacaine included in poly(acrylamide‐co‐monomethyl itaconate) hydrogels as a function of the pH swelling medium

Copolymeric hydrogels of poly(acrylamide‐co‐monomethyl itaconate) (A/MMI) crosslinked with N,N′‐methylenbisacrylamide (NBA) were synthesized as devices for the controlled release of bupivacaine (Bp). Two compositions of the copolymer, 60A/40MMI and 75A/25MMI, were studied. A local anesthetic was included in the feed mixture of polymerization (2–8 mg Bp/tablet) and by immersion of the copolymeric tablets in an aqueous solution of the drug. A very large amount of Bp (36–38 mg Bp/tablet) was included in the gels by sorption due to interactions between the drug and the side groups of the hydrogels. Swelling and drug release were in accordance with the second Fick's law at the first stages of the processes. The swelling behavior of these copolymers depended on the pH of the medium. The equilibrium swelling degree (W_∞) was larger at pH 7.5 (W_∞ ≈ 90 wt %) than at pH 1.5 (W_∞ ≈ 52–64 wt %) due to the ionization of the side groups of the copolymer. Release of the drug also depended on the pH of the swelling medium; at pH 7.5, about 60% of the included drug was released, and at pH 1.5, about 80% was released. Bp release was controlled by the comonomer composition of the gels, their drug‐load, and the pH of the swelling medium. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 327–334, 2002     

Preparation and characterization of pH‐ and temperature‐responsive semi–interpenetrating polymer network hydrogels based on linear sodium alginate and crosslinked poly(N‐isopropylacrylamide)

In this study, pH‐ and temperature‐responsive hydrogels based on linear sodium alginate (SA) and crosslinked poly(N‐isopropylacrylamide) (PNIPAAm) were prepared by semi‐interpenetrating network (semi‐IPN) technique. The dually responsive hydrogels were characterized by FTIR, DSC, and SEM, and their temperature‐ and pH‐responsive behaviors were investigated by measuring equilibrium swelling ratios and pulsatile swelling experiments. The results showed that these hydrogels underwent volume phase transition at around 33°C irrespective of the pH value of the medium, but their pH sensitivity was evident only below their volume phase transition temperature. Under basic conditions, the swelling ratios of SA/PNIPAAm semi‐IPN hydrogels were greater than that of pure PNIPAAm hydrogel and increased with increasing SA content incorporated into the hydrogels, but the case was inverse under acidic conditions. The pulsatile swelling experiments indicated that the higher the SA content in SA/PNIPAAm semi‐IPN hydrogels, the faster the response rate to both pH and temperature change. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1931–1940, 2005     

Use of novel hydrogels based on modified cellulosics and methacrylamide for separation of metal ions from water systems

Interpenetrating networks (IPNs) based on extracted cellulose and its derivatives such as hydroxypropyl cellulose (HPC), cyanoethylcellulose, hydroxyethylcellulose, hydrazinodeoxycellulose, cellulosephosphate with methacrylamide (MAAm), and N,N‐methylene bisacrylamide were synthesized at reaction conditions evaluated for optimum network yield as a function of irradiation dose, concentrations of monomer and crosslinker, and amount of water. These networks were used in sorption of Fe²⁺, Cu²⁺, and Cr⁶⁺ ions. The networks were further functionlized by means of partial hydrolysis with 0.5N NaOH and metal ion sorption studies were carried out. Appreciable amount of all the three ions was sorbed and partial functionalization of the hydrogels results in selectivity in ion sorption with enhanced affinity for Fe²⁺ ions and total rejection of Cr⁶⁺ ions. These results are of interest for the development of low‐cost technologies based on smart hydrogels. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 667–671, 2002