Swelling and mechanical properties of superporous hydrogels of poly(acrylamide-co-acrylic acid)/polyethylenimine interpenetrating polymer networks

Swelling and mechanical properties were investigated for superporous hydrogels (SPHs) of poly(acrylamide-co-acrylic acid)/polyethylenimine (P(AM-co-AA)/PEI) interpenetrating polymer networks (IPNs). Gelation kinetics of SPHs changed significantly according to the acidic condition of reactant. The compressive strength of neutralized SPHs decreased monotonically with AA concentration, while the maximum swelling was observed around the AA weight fraction of 0.4 for all PEI concentrations. The SPH samples composed of high concentrations of AA and PEI were easily cracked in water due to the swelling stress developed during water uptake. The swelling kinetics decreased with increasing PEI and PAA concentrations because of the high molecular entanglement and network density associated with ionic interaction between PAA and PEI molecules. For non-neutralized SPHs, the equilibrium water uptake decreased but the compressive strength increased with PEI and PAA concentrations by simple plasticization effect.     

pH/temperature sensitive poly(ethylene glycol)-based biodegradable polyester block copolymer hydrogels

Novel pH and temperature sensitive biodegradable block copolymers composed of poly(ethylene glycol) (PEG), polyglycolide (GA), ?-caprolactone (CL) and sulfamethazine oligomers (OSMs) were synthesized by ring opening polymerization and 1,3-dicyclohexyl-carbodiimide (DCC) mediated coupling reactions. Their physicochemical properties in aqueous media were characterized by ¹H NMR spectroscopy and gel permeation spectroscopy. The sol-gel phase transition behavior of OSM-PCGA-PEG-PCGA-OSM block copolymers was investigated both in solution and injection to PBS buffer at pH 7.4 and 37 °C. Aqueous solutions of OSM-PCGA-PEG-PCGA-OSM changed from a sol to a gel phase with increasing temperature and decreasing pH. The sol-gel transition properties of these block copolymers are influenced by the hydrophobic/hydrophilic balance of the copolymers, block length, hydrophobicity, stereoregularity of the hydrophobic components within the block copolymer, and the ionization of the pH functional groups in the copolymer, which depends on the environmental pH. Degradation of the triblock and pentablock copolymers at 37 °C (pH 7.4), and at 0 °C and 5 °C both at pH 8.0, was investigated. It was demonstrated here using the in vitro test method, that the anticancer agent paclitaxel (PTX) could be loaded and released by the pH and temperature sensitive OSM-PCGA-PEG-PCGA-OSM block copolymer, such that this could be used as a suitable matrix for subcutaneous injection in drug delivery systems.     

Electrochemical behavior of an interpenetrating polymer network hydrogel composed of poly(propylene glycol) and poly(acrylic acid)

An interpenetrating polymer network (IPN) hydrogel based on poly(propylene glycol) and poly(acrylic acid) was prepared by UV irradiation. The swelling behavior of the IPN hydrogel was studied by the immersion of the gel in aqueous NaCl solutions of various concentrations. The swelling ratio decreased with an increase in the NaCl concentration. The electrically sensitive behavior of the IPN hydrogel in electric fields was also investigated. The IPN hydrogel also showed a stepwise bending behavior that depended on the electric stimulus. The bending angle and bending speed of the IPN hydrogel were greatest in 0.6 wt % aqueous NaCl and increased with an increase in the applied voltage. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2301–2305, 2003     

Characterization of poly(vinyl alcohol)/poly(ethylene glycol) hydrogels and PVA-derived hybrids by small-angle X-ray scattering and FTIR spectroscopy

The purpose of this study is to develop novel poly(vinyl alcohol) (PVA)/poly(ethylene glycol) (PEG) hydrogel blends and PVA-derived organic-inorganic hybrid materials and perform nanostructural characterizations. PVA and PEG hydrogels were prepared by dissolving the polymer in aqueous solution, followed by addition of glutaraldehyde (GA) chemical crosslinker. Hybrids were synthesized by reacting PVA in aqueous solution with tetraethoxysilane (TEOS). PVA/TEOS were also modified in the nanometer-scale by crosslinking with GA during the synthesis reaction. Hydrogels and hybrids were characterized by using small-angle X-ray scattering synchrotron radiation (SAXS) and Fourier transform infrared spectroscopy (FTIR). Thin film samples were prepared for SAXS experiments. SAXS results have indicated different nano-ordered disperse phases for hydrogels made of PVA, PEG, PVA/GA, PVA/PEG. Also, PVA/TEOS and PVA/TEOS/GA hybrids have indicated different X-ray scattering patterns. FTIR spectra have showed major vibration bands associated with organic-inorganic chemical groups present in the hybrid nanocomposites PVA/TEOS and PVA/TEOS/GA. PVA/PEG hydrogels and PVA-derived hybrid materials were successfully produced with GA crosslinking in nanometer-scale network.     

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。     

Scanning electrochemical microscopy measurements of photopolymerized poly(ethylene glycol) hydrogels

Scanning electrochemical microscopy has been used to examine the molecular transport properties of photopolymerized poly(ethylene glycol) (PEG) hydrogels having different mesh sizes. Both the molecular weight (508 Da or 3000 Da) of the PEG diacrylate macromer and its weight percent (20 wt%, 40 wt%, or 60 wt%) in solution prior to photopolymerization were varied. Mesh size was estimated from equilibrium swelling measurements and a thermodynamic model. Estimated mesh sizes ranged from ca. 10 Å for 60 wt% PEG 508 gels to ca. 100 Å for 20 wt% PEG 3000 gels. The electrochemically active diffusing species, ferrocenemethanol, was detected via oxidation at a platinum microelectrode. For a given hydrogel, multiple approach curves showed a consistent relationship between current and distance. Electrochemically estimated diffusivities followed the same trend as predictions based on mesh size and ranged from 25% to 80% of the diffusivity in aqueous solution. As a proof of concept, scanning electrochemical microscopy was successfully used to map the topography of hydrogels with complex architecture, which are being designed as cell scaffolds.     

Synthesis and characteristics of interpenetrating polymer network hydrogel composed of chitosan and poly(acrylic acid)

Interpenetrating polymer network (IPN) hydrogels composed of chitosan and poly(acrylic acid) (PAAc) were synthesized by UV irradiation method, and their structure, crystallinity, swelling behavior, thermal property, and mechanical property were investigated. Chitosan/PAAc IPNs exhibited relatively high equilibrium water content and also showed reasonable sensitivity to pH. From the swelling behaviors at various pH's, Fourier transform infrared spectra at high temperature and thermal analysis confirmed the formation of polyelectrolyte complex due to the reaction between amino groups in chitosan and carboxyl groups in PAAc. For this reason, even at a swollen state, the present chitosan/PAAc IPNs possess good mechanical properties. Particularly, the CA‐2 sample (with a weight ratio of chitosan/PAAc = 50/50, molar ratio [NH₂]/[COOH] = 25/75) showed the lowest equilibrium water content and free water content, attributed to the more compact structure of the polyelectrolyte than CA‐1 or CA‐3 due to the high amount of interchain bond within the IPN. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 113–120, 1999     

Sorption characterization of poly(vinyl alcohol)/chitosan interpenetrating polymer network hydrogels

Poly(vinyl alcohol) (PVA)/chitosan interpenetrating polymer networks (IPN) were prepared by UV irradiation. The water sorption behavior of the IPNs was measured at various temperatures and humidity levels. The water uptake of IPN13 is greater than that of other IPNs. Vapor sorption behavior is more affected by the density of water vapor than by hydrophilic properties with increasing temperature. Equilibrium water uptake increases as humidity increases, and the increase is more noticeable at high humidity. The sorption system of all IPNs is a relaxation‐controlled mechanism at a relative humidity (RH) of 90%, but it is a Fickian diffusion‐controlled mechanism when the RH is below 50%. With an increase in humidity, the diffusion coefficients were found to increase due to greater penetration of water into the IPNs. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 86–90, 2003     

Water sorption of poly(vinyl alcohol)/ poly(diallyldimethylammonium chloride) interpenetrating polymer network hydrogels

Temperature‐responsive interpenetrating polymer network (IPN) hydrogels constructed with poly(vinyl alcohol) and poly(diallyldimethylammonium chloride) using the sequential IPN method were studied. The characteristics of IPN hydrogels were investigated using the dynamic vapor sorption system. IPN hydrogels exhibited a relatively high sorption ratio, 180–360% at room temperature. The sorption ratio of hydrogels depended on temperature. Diffusion coefficients were calculated according to the Fickian Law at several temperatures. The apparent activation energy was 5.43 kJ mol^?1, which corresponds to typical diffusion processes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1389–1392, 2003     

Rapid swelling and deswelling of semi‐interpenetrating network poly(acrylic acid)/poly(aspartic acid) hydrogels prepared by freezing polymerization

Hydrogels with semi‐interpenetrating networks composed of poly(acrylic acid) (PAAc) and poly(aspartic acid) (PASP) have great potential for pharmaceutical and biomedical applications. In this study, we aimed to synthesize semi‐interpenetrating PAAc/PASP hydrogels with improved swelling–deswelling properties via two‐step polymerization, in which the first step of polymerization was performed at 37 °C for 15 min and the second step, the freezing polymerization, was performed at ?20 °C for 24 h. The synthesized hydrogels were characterized with field emission scanning electron microscopy, Fourier transform infrared spectroscopy, and thermogravimetric analysis. The swelling and deswelling behaviors of the hydrogels in response to the ionic strength of the buffer solution were investigated. The Schott's swelling kinetic model was used to elucidate the swelling behavior of the hydrogels. The swelling and deswelling rates of the hydrogels prepared via freezing polymerization were faster than those of the hydrogels prepared via conventional polymerization. This was attributed to the large mean pore size of the freeze‐polymerized hydrogels. The PAAc/PASP hydrogels that underwent freezing polymerization had better swelling–deswelling characteristics than the PAAc hydrogels. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43515.     

Synthesis of full interpenetrating network membranes of poly(acrylic acid-co-acrylamide) in the matrix of polyvinyl alcohol for dehydration of ethylene glycol by pervaporation

Polyvinyl alcohol (PVOH) has been chemically modified by crosslink copolymerization of acrylic acid (AA) and acrylamide (AM) in aqueous solution of PVOH and finally crosslinking the copolymer with methylene bis acrylamide (MBA) and PVOH with glutaraldehyde to produce a full interpenetrating network (FIPN) membrane. Accordingly, three such fully crosslinked IPNs i.e. FIPN25, FIPN50 and FIPN75 have been synthesized with different mass ratio of PVOH:copolymer i.e. 1:0.25 (FIPN25), 1:0.50 (FIPN50) and 1:0.75 (FIPN75). These full IPN membranes were used for pervaporative dehydration of ethylene glycol (EG). All of these IPN membranes were characterized with various conventional methods like FTIR, mechanical properties, DTA and SEM. The performances of the membranes were evaluated in terms of sorption and pervaporative dehydration of EG. The IPN membranes were found to show preferential sorption and diffusion for water. Flux and water selectivity of these membranes were found to increase with increasing amount of copolymer in PVOH matrix. However, among the three membranes, FIPN75 were found to show the highest flux but lower selectivity for water while FIPN50 membrane showed optimum performance in terms of both flux and selectivity. Diffusion coefficient and plasticization interaction of water and EG through all the IPN membranes were determined using modified solution-diffusion model.     

Permeation of solutes through interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylic acid)

The swelling behaviors of poly(vinyl alcohol)–poly(acrylic acid) (PVA–PAAc) interpenetrating networks (IPN) hydrogels in the presence of electrolytes were studied. The ionized carboxylic group within IPN hydrogels at pH 7 strongly interacted with electrolytes in the medium and caused anomalous swelling pattern. The permeabilities of 5 representative solutes were regulated as a function of temperature, pH, ionic strength, solute size, and ionic properties of solutes. The permeation of nonionic solutes followed the swelling behaviors dependent on external stimuli, including the above factors. However, the ionic solutes showed different trends in their permeation through IPN hydrogels. © 1998 John Wiley & Sons, Inc. J Appl Polm Sci 69: 479–486, 1998     

Water behavior of poly(vinyl alcohol)/poly(vinylpyrrolidone) interpenetrating polymer network hydrogels

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) and 1‐vinyl‐2‐pyrrolidone were prepared by radical polymerization with 2,2‐dimethoxy‐2‐phenylacetophenone as a photoinitiator and N,N′‐methylenebisacrylamide as a crosslinker. The IPN hydrogels were analyzed for the sorption behavior of water at 35°C and a relative humidity of 95% with a dynamic vapor sorption system, and water diffusion coefficients were calculated. Differential scanning calorimetry was used to quantitatively determine the amounts of freezing and nonfreezing water. The free‐water contents in the IPN hydrogel samples PV51, PV31, and PV11 were 74.40, 64.03, and 60.48% in pure water, respectively. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 24–27, 2003     

pH-responsive swelling behavior of poly(vinyl alcohol)/poly(acrylic acid) bi-component fibrous hydrogel membranes

The pH-responsive dimensional expansion and mass uptake of bi-component hydrogels in the form of fibrous membranes and films were reported. Fibrous membranes and monolithic films were prepared from aqueous mixture of poly(vinyl alcohol) and poly(acrylic acid) at 3.5 COOH/OH molar composition via electrospinning and solution cast, respectively, then cross-linked by heat-induced esterification. Both forms of hydrogels exhibited increasing swelling with increasing pH. For hydrogel fibrous membranes, planar expansion was immediate without the time lag observed on the films, and equilibrium thickness expansion and mass uptake took far longer than planar expansion. The dimensional expansion in the thickness direction was much higher than that in the planar directions for the fibrous membranes, while they were comparable for monolithic films. The peculiar asymmetric dimensional expansion of fibrous membrane is explicable with the asymmetric distribution of the fibers on the planar and thickness directions, which is formed during layer-by-layer collection process of electrospinning. The fibrous membranes distinguished themselves as being far stronger and faster in re-absorption in the swollen state than the cast-films.     

Preparation of collagen‐immobilized poly(ethylene glycol)/poly(2‐hydroxyethyl methacrylate) interpenetrating network hydrogels for potential application of artificial cornea

To enhance the mechanical strength of poly(ethylene glycol)(PEG) gels and to provide functional groups for surface modification, we prepared interpenetrating (IPN) hydrogels by incorporating poly(2‐hydroxyethyl methacrylate)(PHEMA) inside PEG hydrogels. Formation of IPN hydrogels was confirmed by measuring the weight percent gain of the hydrogels after incorporation of PHEMA, as well as by ATR/FTIR analysis. Synthesis of IPN hydrogels with a high PHEMA content resulted in optically transparent and extensively crosslinked hydrogels with a lower water content and a 6 ～ 8‐fold improvement in mechanical properties than PEG hydrogels. Incorporation of less than 90 wt % PHEMA resulted in opaque hydrogels due to phase separation between water and PHEMA. To overcome the poor cell adhesion properties of the IPN hydrogels, collagen was covalently grafted to the surface of IPN hydrogels via carbamate linkages to hydroxyl groups in PHEMA. Resultant IPN hydrogels were proven to be noncytotoxic and cell adhesion study revealed that collagen immobilization resulted in a significant improvement of cell adhesion and spreading on the IPN hydrogel surfaces. The resultant IPN hydrogels were noncytotoxic, and a cell adhesion study revealed that collagen immobilization improved cell adhesion and spreading on the IPN hydrogel surfaces significantly. These results indicate that PEG/PHEMA IPN hydrogels are highly promising biomaterials that can be used in artificial corneas and a variety of other load‐bearing tissue engineering applications. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Performance of black pigments incorporated in interpenetrating polymer network (IPN)

Interpenetrating polymer network (IPN) in which two different resins (epoxy and silicone) are not miscible as such with each other is made to do so by using cross-linking agents and catalyst. IPN possess good improved mechanical, chemical, heat and corrosion resistant properties than individual resins. Incorporation of black pigments like graphite, silicon carbide, carbon black and acetylene black has enhanced these properties because of their shape, size, acid and salt solution resistance, conducting nature and heat stability property. Flake structured graphite and hexagonal structured silicon carbide pigments in IPN protect the mild steel structures from corrosive and high temperature atmosphere for longer duration than the other pigments.     

Thermo-oxidative degradation of poly(ethylene glycol)/poly( -lactic acid) blends

The thermo-oxidative degradation of poly(ethylene glycol)/poly( -lactic acid) (PEG/PLLA) blends was studied by infra-red spectroscopy (IR), differential scanning calorimetry (DSC), gel permeation chromatography (GPC) and thermogravimetry (TGA). The thermo-oxidative degradation of PEG occurred after a period time of aging in air at 80 °C. The mechanism of thermo-oxidative degradation of PEG was found to be the random chain scission of the main chain. As PEG blending with PLLA, the existence of PLLA appeared to enhance the thermo-oxidative degradation of PEG. The enhancement of thermo-oxidative degradation increased first and then decreased with the increase of PLLA. The results could be attributed to the ease of abstraction of the carboxylic hydrogen (–COOH) of PLLA, which enhanced the thermo-oxidative degradation of PEG. Also, the dilution effect of PLLA on the concentration of free radicals was an important factor of the thermo-oxidative degradation.     

Dynamic swelling of hydrogels based on random terpolymers of N-isopropylacrylamide, methacrylic acid and poly(ethylene glycol) macromonomer

A series of pH-responsive hydrogels based on N-isopropylacrylamide (N-iPAAm), methacrylic acid (MAA) and poly(ethylene glycol) monomethyl ether monomethacrylate macromonomer (PEGMEMA), P(N-iPAAm-co-MAA-co-PEGMEMA) random terpolymers, were synthesized and their swelling behaviour studied as a function of both monomer composition and previous swelling treatment. The swelling kinetic curves were followed using gravimetric, photographic and magnetic resonance imaging (MRI) techniques, which provide spatial and temporal resolution. The swelling behaviour was non-Fickian at pH 7, being this fact more relevant when the samples were pre-soaked in pH 2 solution. Low pH promotes hydrogen bond arrangements that disrupt at pH 7, where sigmoidal swelling curves were observed. The sigmoidal shape of the curves increases as well as the swelling time with increasing N-iPAAm/PEGMEMA ratio. This indicates that hydrogen bond arrangements between MAA and N-iPAAm are stronger that those formed by MAA and PEGMEMA. The influence of the polymer composition on the hydrogen bond arrangements was also studied from the swelling kinetics curves at different pH media, observing that the swelling rate, the swelling curve shape and the whole amount of water absorbed were clearly dependent on this parameter.     

Preparation and characterization of heat-resistant interpenetrating polymer network (IPN)

Interpenetrating polymer network (IPN) is a novel type of polymer hybrids, which possess physicochemical properties suitable for high performance coatings. Heat-resistant IPN have been prepared from immiscible resins, epoxy and silicones using a cross-linking agent and a catalyst. The products were analyzed by GPC, FT-IR, TG, DTA and SEM studies. The heat resistance property and corrosion behaviour of the IPNs were also determined. It was different from those of the individual resins. Silicone microdomains could be seen uniformly distributed in epoxy regions. Corrosion resistance property of the IPNs was evaluated by salt spray and impedance measurements. The IPNs withstood longer durations in the salt spray chamber.     

Preparation and characterizations of interpenetrating polymer network hydrogels of poly(ethylene oxide) and poly(methyl methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(ethylene oxide) and poly(methyl methacrylate) were prepared by radical polymerization using 2,2‐dimethyl‐2‐phenylacetophenone and ethylene glycol dimethacrylate as initiators and crosslinkers, respectively. The IPN hydrogels were analyzed for sorption behavior at 25°C and at a relative humidity of 95% using dynamic vapor sorption. The IPN hydrogels exhibited a relatively high equilibrium water content in the range of 13–68%. The state of water in the swollen IPN hydrogels was investigated using differential scanning calorimetry. The free water in the hydrogels increased as the hydrophilic content increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 258–262, 2003