Smart carboxymethylchitosan hydrogels that have thermo‐ and pH‐responsive properties

Thermo‐responsive poly(N‐isopropylacrylamide) (poly(NIPAAm)) and pH‐responsive poly(N,N′‐diethylaminoethyl methacrylate) (poly(DEAEMA)) polymers were grafted to carboxymethylchitosan (CMC) via radical polymerization to form highly water swellable hydrogels with dual responsive properties. Ratios of CMC, NIPAAm to DEAEMA used in the reactions were finely adjusted such that the thermo and pH responsiveness of the hydrogels was retained. Scanning electron microscopy (SEM) indicated the formation of an internal porous structure for the swollen CMC hydrogels upon incorporation of poly(NIPAAm) and poly(DEAEMA). Effect of temperature and pH changes on water swelling properties of the hydrogels was investigated. It was found that the water swelling of the hydrogels was enhanced when the solution pH was under basic conditions (pH 11) or the temperature was below its lower critical solution temperature (LCST). These responsive properties can be used to regulate releasing rate of an entrapped drug from the hydrogels, a model drug, indomethacin was used to demonstrate the release. These smart and nontoxic CMC‐based hydrogels show great potential for use in controlled drug release applications with controllable on‐off switch properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41505.     

Characterization and caffeine release properties of N‐isopropylacrylamide/hydroxypropyl methacrylate copolymer hydrogel synthesized by gamma radiation

Research efforts have been devoted to demonstrate that the temperature sensitivity characters of poly(N‐isopropylacrylamide)(PNIPAAm) can be applied in the field of drug carriers. A copolymer hydrogel of N‐isopropylacrylamide/hydroxypropyl methacrylate (NIPAAm/HPMA) was synthesized by gamma irradiation. The nature of bonding was characterized by FTIR spectroscopy, whereas the thermal stability was characterized by thermogravimetric analysis (TGA). The influence of NIPAAm/HPMA composition on the swelling properties in water, at different temperatures and different pH values was studied. The release characters of caffeine drug from NIPAAm/HPMA hydrogels were also investigated. The gel fraction of NIPAAm/HPMA was found to increase slightly by increasing the ratio of HPMA in the initial solution. The IR spectra indicate the formation of copolymer hydrogels, whereas the TGA study showed that the NIPAAm/HPMA copolymer hydrogels displayed higher thermal stability than NIPAAm hydrogel. PNIPAAm hydrogel showed higher swelling in water than NIPAAm/HPMA hydrogels. Based on Fick's law, it was demonstrated that the diffusion of water into NIPAAm/HPMA is controlled. It was found that the main parameters affecting the drug release behavior from the hydrogels are composition and pH. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermo‐responsive injectable hydrogel system based on poly(N‐isopropylacrylamide‐co‐vinylphosphonic acid). I. Biomineralization and protein delivery

To achieve the injectable hydrogel system in order to improve bone regeneration by locally delivering a protein drug including bone morphogenetic proteins, thermo‐responsive injectable hydrogels composed of N‐isopropylacrylamide (NIPAAm) and vinyl phosphonic acid (VPAc) were prepared. The P(NIPAAm‐co‐VPAc) hydrogels were also biomineralized by urea‐mediation method to create functional polymer hydrogels that deliver the protein drug and mimic the bone extracellular matrix. The loosely cross‐linked P(NIPAAm‐co‐VPAc) hydrogels were pliable and fluid‐like at room temperature and could be injected through a small‐diameter aperture. The lower critical solution temperature (LCST) of P(NIPAAm‐co‐VPAc) hydrogel was influenced by the monomer ratio of NIPAAm/VPAc and the hydrogel with a 96/4 molar ratio of NIPAAm/VPAc exhibited an LCST of ～34.5°C. Water content was influenced by temperature, NIPAAm/VPAc monomer ratio, and biomineralization; however, all hydrogels maintained more than about 77% of the water content even at 37°C. In a cytotoxicity study, the P(NIPAAm‐co‐VPAc) and biomineralized P(NIPAAm‐co‐VPAc) hydrogels did not significantly affect cell viability. The loading content of bovine serum albumin in hydrogel, which was used as a model drug, gradually increased with the amount of VPAc in the hydrogel owing to the ionic interaction between VPAc groups and BSA molecules. In addition, the release behavior of BSA from the P(NIPAAm‐co‐VPAc) hydrogels was mainly influenced by the drug loading content, water content, and biomineralization of the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Rheological properties of poly(ethylene glycol)/poly(N‐isopropylacrylamide‐co‐2‐acrylamido‐2‐methylpropanesulphonic acid) semi‐interpenetrating networks

For the increasing demands of multifunctional materials in applications such as drug delivery system, a pH‐ and temperature‐responsive polyelectrolyte copolymer gel system was studied using rheometry. Rheological properties, determined by plate–plate rheometry in oscillatory shear, of hydrogels formed by free radical initiated copolymerization of N‐isopropylacrylamide (NIPA) and 2‐acrylamido‐2‐methylpropanesulphonic acid (AMPS) in the presence of methylene bisacrylamide (MBAA) as crosslinker are compared with the properties of semi‐interpenetrating network (SIPN) polyelectrolyte gels made by incorporation of poly(ethylene glycol) with molar mass 6000 g mol^?1 (PEG6000). Based on our systematic studies for this PEG/SIPN system, the effects of initiator and crosslinker concentration, relative proportions of comonomer units in the main chains, PEG6000 content and temperature on viscoelastic properties, unusual high storage moduli at small strain for the SIPN were discussed. The SIPN gel with characteristics of PEG molecules as well as pH and temperature responsiveness from AMPS and NIPA units has potential application in drug delivery system design. Ice‐like rheological behavior of the PEG/AMPS‐NIPA SIPN gels at low temperature was first time reported and water remains homogeneous without phase separation in PEG/AMPS‐NIPA SIPN hydrogels at low temperature may be considered as an ideal candidate for water storage material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermo‐ and pH‐ responsive copolymers: Poly(n‐Isopropylacrylamide‐co‐IAM) copolymers

Poly(N‐isopropylacrylamide) (NIPAAm) is well known as a smart material with good thermal sensitivity and favorable biocompatibility. A series of new smart hydrogels, NIPAAm copolymerized with IAM (itaconamic acid; 4‐amino‐2‐methylene‐4‐oxobutanoic acid), were synthesized through radical solution polymerization in this work. Poly(NIPAAm‐co‐IAM) can respond to the changes of temperature as well as pH value. Such a characteristic is due to the fact that IAM contains not only a hydrophilic acrylic acid moiety but also an acrylamide moiety to be thermal and pH sensitive. The experimental results show that the lower critical solution temperature (LCST) of the copolymer increases as the molar fraction of IAM increases. Moreover, based on the current experimental data, 3 wt % of Poly(NIPAAm‐co‐IAM) aqueous solution in this study exhibits a phase transition temperature (37.8°C) close to the human body temperature in the buffer solution of pH 7 possibly to be useful in drug delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42367.     

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     

Swelling properties of CMC‐g‐poly (AAm‐co‐AMPS) superabsorbent hydrogel

A series of biopolymer‐based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free‐radical graft copolymerization of acrylamide and 2‐acrylamido‐2‐methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT‐IR spectroscopy and scanning electron microscope analysis were used to confirm the hydrogel structure. Swelling measurements of the synthesized hydrogels in different salt solutions indicated considerable swelling capacity. The absorbency under load of the superabsorbent hydrogels was determined by using an absorbency under load tester at various applied pressures. A preliminary swelling and deswelling behaviors of the hydrogels were also studied. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and properties of P(NIPAAm‐co‐AM)/SiO2 hybrid temperature‐sensitive hydrogels

Using N, N′‐methylene bisacrylamide as crosslinking agent and potassium peroxydisulfate as initiator, the temperature‐sensitive hydrogels were prepared with organic monomer N‐isopropylacrylamide (NIPAAm) and acrylic amide and inorganic material ethyl orthosilicate (TEOS). The structure of hybrid hydrogels was represented by scanning electron microscopy and Fourier transform infrared spectroscopy. The volume phase transition temperature (VPTT) of hybrid hydrogels was determined by differential scanning calorimetry thermograms of the swollen hydrogel. The results showed that the VPTT of the hydrogels increased with the increasing of TEOS dosage. When the temperature was lower than VPTT, the hydrogels exhibited excellent temperature sensitivity and kept at a swelling state, but when the temperature was higher than VPTT, the hydrogels deswelled significantly. In addition, the compressive strength of hydrogels was studied, the results showed that hybrid hydrogels had more ideal mechanical properties than organic hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of intercalated hydrotalcite on swelling and mechanical behavior for poly(acrylic acid‐co‐N‐isopropylacrylamide)/hydrotalcite nanocomposite hydrogels

A series of nanocomposite hydrogels were prepared from acrylic acid (AA), N‐isopropylacrylamide (NIPAAm), and intercalated hydrotalcite (IHT) by photopolymerization. The influence of the intercalating content of 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) in HT on the swelling and mechanical properties for poly(AA‐co‐NIPAAm)/IHT nanocomposite hydrogels was investigated. The results showed that the higher the content of the AMPS‐HT was, the higher the swelling ratio of the gels and the higher the content of the intercalating agent was, the lower swelling ratio. It was also demonstrated that the swelling ratio of the gel was not affected by the counterion in HT. The gel strength and crosslinking density were not enhanced by adding AMPS‐HT into the gel composition, but the maximum effective crosslink density and shear modulus of the nanocomposite hydrogels were increased with an increase of the content of the intercalating agent in HT. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1572–1580, 2005     

Thermosensitive poly(n‐isopropylacrylamide) hydrogels bonded on cellulose supports

A two‐step initiation and polymerization process was developed for the preparation of two series of hydrogel–cellulose composites with distinctively different morphologies and swelling behaviors. Hydroentangled cotton cellulose fibers were optimally initiated in 20 mM aqueous ammonium cerium(IV) nitrate for 15 min and then polymerized in aqueous solutions of N‐isopropylacrylamide (NIPAAm) monomer and N,N′‐methylene bisacrylamide (BisA) crosslinker. The extents of hydrogels on the cellulose solids could be controlled by variations in the concentrations of the monomer and crosslinker as well as the NIPAAm/BisA solution‐to‐solid ratios. The two series of hydrogel–cellulose composites formed were hydrogel‐covered/filled cellulose (I) and cellulose‐reinforced hydrogel (II) composites. Series I composites were synthesized with NIPAAm/BisA solutions below the liquid saturation level of the cellulose; this led to pore structures (size and porosity) that depended on both the extent and swelling of the grafted hydrogels. Series II composites were polymerized in the presence of excessive NIPAAm/BisA solutions to produce cellulose solids completely encapsulated in the hydrogels. All the cellulose‐supported hydrogels exhibited lower extents of phase transition over a wider temperature range (28–40°C) than the free poly(N‐isopropylacrylamide) hydrogels (32°C). These findings demonstrate that hydrogels can be used to control the pore structure of cellulose and can be supported with cellulose fibers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 999–1006, 2003     

Removal of hazardous by radiation‐synthesized copolymer hydrogels based on 2‐acrylamido‐2‐methylpropanesulfonic acid and 2‐dimethyaminoethyl methacrylate monomers

Superabsorbent copolymer hydrogels were prepared by gamma irradiation of aqueous solutions of 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) and 2‐dimethyaminoethyl methacrylate (DEMA) monomers mixtures. The thermal stability of hydrogels was evaluated by thermogravimetric analysis. The ability to adsorb Cu²⁺ ions and dyes by the prepared hydrogels from aqueous solutions was investigated. The swelling study, in water, showed that the hydrogels based on pure AMPS monomer and AMPS/DEMA copolymers reached the equilibrium state after 6 h. However, the hydrogel based on pure AMPS monomer showed higher swelling than the copolymer hydrogels based on AMPS/DEMA. It was found that the copolymer hydrogels based on different compositions showed affinity to absorb Cu²⁺ metal ions as well as basic and acid dyes; however, this affinity was found to decrease with increasing the ratio of DEMA in the initial feeding solutions. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Removal of heavy metals from model wastewater by using carboxymehyl cellulose/2‐acrylamido‐2‐methyl propane sulfonic acid hydrogels

A series of functional copolymer hydrogels composed of carboxymethyl cellulose (CMC) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) were synthesized using γ‐radiations‐induced copolymerization and crosslinking. Preparation conditions were optimized, and the swelling characteristics were investigated. The ability of the prepared hydrogels to recover some toxic metal ions from their aqueous solutions was studied. The prepared hydrogel showed a great capability to recover metal ions such as: Mn⁺², Co⁺², Cu⁺², and Fe⁺³ from their solutions. The data revealed that the chelating ability of the prepared hydrogels is mainly dependent on their internal composition, in addition to the physical properties of the metal ion solution such as pH and metal ion concentration. The data show that the chelating ability of the prepared hydrogels increases by increasing the AMPS content in the hydrogel as well as the increment in the pH of the solution and the metal ion concentration. The prepared CMC/AMPS copolymer hydrogels are chemically stable enough to be reused for at least five times with the same efficiency. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Novel thermosensitive hydrogel composites based on poly(d,l‐lactide‐co‐glycolide) nanoparticles embedded in poly(n‐isopropyl acrylamide) with sustained drug‐release behavior

To reach sustained drug release, a new composite drug‐delivery system consisting of poly(d,l ‐lactide‐co‐glycolide) (PLGA) nanoparticles (NPs) embedded in thermosensitive poly(N‐isopropyl acrylamide) (PNIPAAm) hydrogels was developed. The PNIPAAm hydrogels were synthesized by free‐radical polymerization and were crosslinked with poly(ethylene glycol) diacrylate, and the PLGA NPs were prepared by a water‐in‐oil‐in‐water double‐emulsion solvent‐evaporation method. The release behavior of the composite hydrogels loaded with albumin–fluorescein isothiocyanate conjugate was studied and compared with that of the drug‐loaded neat hydrogel and PLGA NPs. The results indicate that we could best control the release rate of the drug by loading it to the PLGA NPs and then embedding the whole system in the PNIPAAm hydrogels. The developed composite hydrogel systems showed near zero‐order drug‐release kinetics along with a reduction or omission of initial burst release. The differential scanning calorimetry results reveal that the lower critical solution temperature of the developed composite systems remained almost unchanged (<1°C increase only). Such a characteristic indicated that the thermosensitivity of the PNIPAAm hydrogel was not distinctively affected by the addition of PLGA NPs. In conclusion, an approach was demonstrated for the successful preparation of a new hybrid hydrogel system having improved drug‐release behavior with retained thermosensitivity. The developed systems have enormous potential for many biotechnological applications. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40625.     

Photo‐cross‐linked biodegradable thermo‐ and pH‐responsive hydrogels for controlled drug release

A new strategy was developed to prepare thermo‐ and pH‐sensitive hydrogels by the crosslinking of poly(N‐isopropylacrylamide) with a biodegradable crosslinker derived from poly(L ‐glutamic acid). Hydrogels were fabricated by exposing aqueous solutions of precursor containing photoinitiator to UV light irradiation. The swelling behaviors of hydrogels at different temperatures, pHs, and ionic strengths were examined. The hydrogels shrank under acidic condition or at temperature above their collapse temperature and would swell in neutral or basic media or at lower temperature. These processes were reversible as the pH or temperature changed. All hydrogels exhibited no weight loss in the simulated gastric fluid but degraded rapidly in the simulated intestinal condition. Bovine serum albumin were used as a model protein drug and loaded into the hydrogels. The in vitro drug release experiment was carried out at different pH values and temperatures. The pH and temperature dependent release behaviors indicated the promising application of these materials as stimuli‐responsive drug delivery vehicles. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

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

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

Radiation polymerization and concentration separation of P(NIPA‐co‐AMPS) hydrogels

Extraction or concentration with temperature‐sensitive hydrogels is a novel separation technology. In this study, N‐isopropylacrylamide (NIPA) was synthesized by acrylonitrile and isopropanol. Poly(N‐isopropylacrylamide) (PNIPA) and copolymer of NIPA and 2‐acrylamide‐2‐methylpropane sulfonate [P(NIPA‐co‐AMPS)] hydrogels were prepared by radiation polymerization. Dependence of their swelling behavior on temperature was studied. Effects of radiation dose on polymerization, feed composition on thermoresponse, electrolyte on relative swelling ratio, and swelling and deswelling kinetics were investigated. The experimental results showed that P(NIPA‐co‐AMPS) hydrogels with low content of AMPS/NIPA (1–5 %), prepared at a radiation dose‐rate of 1 kGy/h and total dose of 30–40 kGy, could enhance the swelling ratio of PNIPA hydrogels significantly and raise the phase‐transition temperatures. P(NIPA‐co‐AMPS) hydrogels produced under optimum conditions were used to concentrate aqueous bovine serum albumin (BSA, M = 69 000 g mol^?1) solution. When aqueous BSA concentration was below 5 %, the separation efficiency was more than 80 % with low cost and low energy consumption. Copyright © 2005 Society of Chemical Industry     

Synthesis and swelling behavior of thermosensitive IPN hydrogels based on sodium acrylate and N‐isopropyl acrylamide by a two‐step method

A series of interpenetrating polymer network (IPN) hydrogels having higher swelling ratio (SR) and thermosensitivity were synthesized from sodium acrylate (SA) and N‐isopropyl acrylamide (NIPAAm) by a two‐step method. A series of the porous poly(sodium acrylate ‐co‐1‐vinyl–2‐pyrrolidone) [poly(SA‐co‐VP)], (SV), hydrogels were prepared from acrylic acid having 90% degree of neutralization and VP monomer in the first step. The second step is to immerse the SV dried gels into the NIPAAm solution containing initiator, accelerator, and crosslinker to absorb NIPAAm solution and then polymerized to form the poly(SA‐co‐VP)/poly(NIPAAm) IPN hydrogels (SVN). The effect of the different molar ratios of SA/VP and the content of NIPAAm on the swelling behavior and physical properties of the SVN hydrogels was investigated. Results showed that the SVN hydrogels displayed an obviously thermoreversible behavior when the temperature turns across the critical gel transition temperature (CGTT) of poly(NIPAAm) hydrogel. The pore diameter distributions inside the hydrogel also indicated that the pore sizes inside the SVN hydrogels were smaller than those inside the SV hydrogels. At the same time, the more proportion of SA was added into the hydrogel, the larger pore diameter of the SV hydrogel was formed. The results also showed that the SR decreased with an increase of the VP content in the SV hydrogel and more obviously decreased in the SVN hydrogels. The SVN networks also showed stronger shear moduli than SV hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

A new composite sorbent for water and dye uptake: Highly swollen acrylamide/2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid/clay hydrogels crosslinked by 1,4‐butanediol dimethacrylate

A novel type of highly swollen hydrogels based on acrylamide (AAm) with 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) and clay such as bentonite (Bent) crosslinked by 1,4‐butanediol dimethacrylate (BDMA) was prepared by free radical solution polymerization in aqueous media. Water uptake and dye sorption properties of polyelectrolyte AAm/AMPS hydrogels and AAm/AMPS/Bent composite hydrogels were investigated as a function of composition to find materials with swelling and sorption properties. FTIR analyses were made. Swelling experiments were performed in water and dye solution at 25°C, gravimetrically. Highly swollen AAm/AMPS and AAm/AMPS/Bent hydrogels were used in experiments on sorption of water‐soluble monovalent cationic dye such as Lauths violet “LV, (Thionin).” Swelling of AAm/AMPS hydrogels was increased up to 1,920–9,222% in water and 867–4,644% in LV solutions, while AAm hydrogels swelled 905% in water and swelling of AAm/AMPS/Bent hydrogels was increased up to 2,756–10,422% in water and 1,200–3,332% in LV solutions, while AAm/Bent hydrogels swelled 849% in water. Some swelling kinetic and diffusional parameters were found. Water and LV diffusion into hydrogels was found to be non‐Fickian in character. For sorption of cationic dye, LV into AAm/AMPS and AAm/AMPS/Bent hydrogel was studied by batch sorption technique at 25°C. The amount of the dye sorbed per unit mass removal effiency and partition coefficient of the hydrogels was investigated. The influence of AMPS content in the hydrogels to sorption was examined. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

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     

Preparation of thermosensitive and superabsorbent polymer hydrogels from trialkyl‐4‐vinylbenzyl phosphonium chloride‐N‐isopropylacrylamide‐N,N′‐methylenebisacrylamide copolymers and their properties

Thermosensitive and superabsorbent polymer hydrogels were synthesized by copolymerization of three kinds of tri‐n‐alkyl vinylbenzyl phosphonium chlorides (TRVB) with different lengths of alkyl chains, N‐isopropylacrylamide (NIPAAm), and N,N′‐methylenebisacrylamide (MBAAm). The water‐absorption ability and antibacterial activity of the hydrogels against Staphylococcus aureus (S. aureus) were investigated. The water content of TRVB–NIPAAm–MBAAm copolymers decreased with increasing temperature and increased with increasing phosphonium groups in the copolymers, while it decreased with increasing chain length of the alkyl groups in the phosphonium groups as well as with an increasing degree of crosslinking in the copolymers. The TRVB–NIPAAm–MBAAm copolymers with a higher TRVB content in the copolymers exhibited higher antibacterial activity against S. aureus, but decreased with increasing chain length of alkyl groups in phosphonium groups. The TRVB–NIPAAm–MBAAm copolymers exhibited the highest antibacterial activity at 30°C against S. aureus in deionized water. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 115–124, 2001