Characterization of structured acrylamide/acrylic acid hydrogels by TMDSC and microscopy

The thermal behavior of hydrogels synthesized by solution polymerization between acrylamide, acrylic acid and diglycidyl acrylate (DGA) as a crosslinking agent was investigated. The structure of the hydrogel can be tightly controlled with the reaction temperature. This method produces a new type of hydrogels, which exhibit well defined structures at various scales of length simultaneously. These multi-structured hydrogels are hydrophilic, elastic, water insoluble, and soft polymers with an anisotropic optical response. The structure was observed by scanning electron microscopy (SEM), polarized light microscopy (PLM) and macroscopic visualization (CCD camera). In addition, structural transitions in the hydrogels were monitored by temperature modulated differential scanning calorimetry (TMDSC). Severe heating tests in an adiabatic oven were performed to analyze decomposition of the material. Fourier transform infrared (FTIR) spectroscopy was used to qualitatively analyze the hydrogels samples exposed to a sudden thermal treatment.     

Water uptake and dye sorption studies of chemically crosslinked highly swollen novel ternary acrylamide‐based hydrogels including citraconic acid and sodium acrylate

Highly swollen hydrogels made by the polymerization of acrylamide (AAm) with some anionic monomers such as citraconic acid (CITA) and sodium acrylate (SA) were investigated as a function of composition to find materials with swelling and dye sorption properties. Highly swollen AAm/CITA/SA or AAm/SA/CITA hydrogels were prepared by free radical solution polymerization in aqueous solutions of AAm with CITA and SA as co‐monomers and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. Chemically crosslinked AAm/CITA/SA or AAm/SA/CITA hydrogels were used in experiments on sorption of water‐soluble monovalent cationic dye such as “Nil blue” (Basic Blue 12; BB 12). Equilibrium percentage swelling values of AAm/CITA/SA or AAm/SA/CITA hydrogels were calculated in the range of 1797–22,098%. Some swelling kinetic parameters were found. Diffusion behavior of water was investigated. Water diffusion into the hydrogels was found to be non‐Fickian in character. For sorption of cationic dye, BB 12 into the hydrogels was studied by batch sorption technique at 25°C. AAm/CITA/SA or AAm/SA/CITA hydrogels in the dye solutions showed coloration, whereas AAm hydrogel did not show sorption of any dye from the solution. The sorption capacity of AAm/CITA/SA or AAm/SA/CITA hydrogels was investigated. At the end of the experiments, 21.70–78.91% BB 12 adsorptions were determined. Copyright © 2007 John Wiley & Sons, Ltd.     

Swelling characterization of novel ternary semi‐IPNs: acrylamide/1‐vinylimidazole/PEG hydrogels

New ternary semi interpenetrating polymer networks (semi‐IPNs) systems containing acrylamide (AAm), 1‐vinylimidazole (VI) and poly (ethylene glycol) (PEG) have been prepared. AAm/VI hydrogels and semi‐IPN's, poly (AAm/VI/PEG) with 0.25, 0.50, 0.75 and 1.00 g of PEG (per 1.00 g AAm) were prepared by free radical solution polymerization in aqueous solution of AAm with VI as comonomer and a multifunctional crosslinker such as 1,4 butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of VI and PEG content in hydrogels were examined. AAm/VI and AAm/VI/PEG hydrogels showed large extents of swelling in aqueous media, the swelling being highly dependent on the chemical composition of the hydrogels. Percentage swelling ratio of AAm/VI hydrogels and AAm/VI/PEG hydrogels was shown as 650–4167%. The values of equilibrium water content (EWC) of the hydrogels are between 0.8990 and 0.9750. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and characterization of physically crosslinked N‐vinylcaprolactam,acrylic acid,methacrylic acid,and N,N‐dimethylacrylamide hydrogels

Physically crosslinked hydrogels based on N‐vinylcaprolactam/acrylic acid and N‐vinylcaprolactam/methacrylic acid were prepared via free radical polymerization. These temperature responsive hydrogels were characterized in terms of glass transition, phase separation temperature, potentiometric titration and swelling properties. Results showed that phase transition temperature was dependent on the pH value of the solution; increasing pH led to higher lower critical solution temperature (LCST) values which was related to the dissociative behaviors of the carboxylic group of MAc in the buffered solutions. Additionally, with the incorporation of N,N‐dimethylacrylamide into the system, cloud point measurements and MDSC showed an increased in the LCST. This increase was based on hydrophilicity, the hydrophilic–hydrophobic balance was disturbed, and consequently, the LCST behavior was shifted. The pKa of the copolymers ranged between 5.6 and 6.5, while for the terpolymers pKa ranged between 5.3 and 6. At high pH (>10), the ? COOH group is deprotonated and negatively charged (? COO^?), while at low pH (1–3) the carboxylic group remains protonated which results in hydrogen bonding between the hydroxyl groups (from NaOH) and the excess of HCl. These results correlate with swelling studies where above the pKa value the hydrogels dissolved rapidly compared to below pKa they did not dissolve at all. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1555–1564     

Synthesis and characterization of poly(acrylic acid‐co‐acrylamide)/hydrotalcite nanocomposite hydrogels for carbonic anhydrase immobilization

To combine the advantages of a biopolymer with hydrotalcite in an enzyme immobilization system, the intercalation polymerization was used to prepare poly(acrylic acid‐co‐acrylamide)/hydrotalcite (PAA‐AAm/HT) nanocomposite hydrogels using sodium methyl allyl sulfonate as intercalation agent. Transmission electron microscopy, X‐ray diffraction, and Fourier transform infrared spectroscopy results revealed that sodium methyl allyl sulfonate chains entered into the interlayer of HT, the interaction between them has taken place, and HT was dramatically exfoliated into nanoscale and homogeneously dispersed in the PAA‐AAm matrix. Transmission electron microscopy and cryo scanning electron microscope results showed that dried hydrogels were regular spherical particles, and swollen hydrogels revealed homogeneous porous network structures. Then, PAA‐AAm/HT nanocomposite hydrogels were used to immobilize carbonic anhydrase (CA), and the CO₂ hydration activities of free enzyme and immobilized enzyme were evaluated. Results showed that immobilized CA retained the majority of the enzyme activity. The reason may be the formation of a microenvironment almost all of which is composed of free water inside the porous network structures. Therefore, the immobilized CA is of great potential in the removal of trace CO₂ from the closed spaces. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3232–3240, 2009     

Synthesis and characterization of novel biodegradable unsaturated poly(ester amide)/poly(ethylene glycol) diacrylate hydrogels

A series of novel biodegradable hydrogels were designed and synthesized from four types of unsaturated poly(ester amide) (UPEA) and poly(ethylene glycol) diacrylate (PEG‐DA) precursors by UV photocrosslinking. These newly synthesized biodegradable UPEA/PEG‐DA hydrogels were characterized by their gel fraction (G_f), equilibrium swelling ratio (Q_eq), compressive modulus, and interior morphology. The effect of the precursor feed ratio (UPEAs to PEG‐DA) on the properties of the hydrogels was also studied. The incorporation of UPEA polymers into the PEG‐DA hydrogels increased their hydrophobicity, crosslinking density (denser network), and mechanical strength (higher compressive modulus) but reduced Q_eq. When different types of UPEA precursors were coupled with PEG‐DA at the same feed ratio (20 wt %), the resulting hydrogels had similar Q_eq values and porous three‐dimensional interior morphologies but different G_f and compressive modulus values. These differences in the hydrogel properties were correlated to the chemical structures of the UPEA precursors; that is, the different locations of the >C?C< double bonds in individual UPEA segments resulted in their different reactivities toward PEG‐DA to form hydrogels. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3932–3944, 2005     

Synthesis and properties of poly(acrylamide‐co‐acrylic acid)/polyacrylamide superporous IPN hydrogels

Poly(acrylamide‐co‐acrylic acid)/polyacrylamide [P(AM‐co‐AA)/PAM] hydrogel with superporous and interpenetrating network (IPN) structure was prepared by a prepolymerization reaction and a synchronous polymerization reaction and frothing process. Scanning electron microscope (SEM) images show that the resultant hydrogel possesses abundant interconnected pores. DSC indicates that the porous structure enhances the swelling ratio and reduces the interaction between water and the hydrogel. In contrast, the IPN by PAM decreases water absorbency and enhances water retentivity. It is found that a superporous stucture in the hydrogel increases the equilibrium swelling ratio and decreases the compressive strength of the hydrogel. On the other hand, the increase in AM oligomer (oligo‐AM) amount decreases the equilibrium swelling ratio and improves the compressive strength of the hydrogel. Therefore, the two‐steps synthesis method can be used to construct a hydrogel with superporous and IPN structure. The swelling and mechanical properties of the hydrogel can be improved effectively. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of poly(N‐vinyl formamide) hydrogels—A potential alternative to polyacrylamide hydrogels

The synthesis and characterization of solution‐cast, molded gels of N‐vinyl formamide (NVF) has not been previously reported even though NVF is an isomer of acrylamide (AAm) and polyacrylamide (PAAm) hydrogels have many commercial applications. Aqueous NVF solutions were cross‐linked into gels using a novel cross‐linker, 2‐(N‐vinylformamido)ethylether, and the thermally‐activated initiator VA‐044. For a given formulation, PNVF gels swell up to twice that of PAAm gels cross‐linked with N,N′‐methylenebisacrylamide. From swelling and compression measurements, PNVF gels were found to be more hydrophilic than PAAm gels. Flory‐Huggins solubility parameters were χ = 0.38?₂ + 0.48 for PNVF and χ = 0.31?₂ + 0.49 for PAAm, where ?₂ is the polymer volume fraction. The shear moduli for PNVF and PAAm scale with ? and ? respectively, consistent with good solvent behavior, also suggesting PNVF is more hydrophilic than PAAm. Similarity of mechanical properties for both gels as a function of ?₂ suggests that network structures of PNVF and PAAm gels are similar. Fracture strains of both gels declined with ?₂ by the same linear function while fracture stresses were about 500 kPa regardless of formulation. Since NVF is a liquid monomer, less toxic than AAm and can be hydrolyzed to a cationic form, PNVF gels could become technologically significant. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis of a new hyperbranched,vinyl macromonomer through the use of click chemistry: Synthesis and characterization of copolymer hydrogels with PEG diacrylate

A new biodegradable, water‐soluble macromonomer based on the commercial hyperbranched polyester Boltorn^®H20 has been synthesized through the use of click chemistry. The macromonomer was developed with the aim of being injected with a comacromonomer, poly(ethylene glycol) (PEG) diacrylate, for in situ copolymerization to form biodegradable polymer hydrogels. Copolymer hydrogels were prepared from the macromonomer and PEG diacrylate (FW 700) by free radical copolymerization. A degree of phase separation of the hydrogels was observed during polymerization and with increasing incorporation of the Boltorn macromonomer an increasing tendency for the formation of macropores was observed. The swelling ratios of the gels in water and phosphate buffered saline solution, PBS, all increase with increasing Boltorn macromonomer concentration, as did the penetrant diffusion coefficients and the degradation rate in PBS. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and metal binding behavior of hydroxamic acid resins from poly(ethyl acrylate) crosslinked with divinylbenzene and hydrophilic crosslinking agent

Porous poly(hydroxamic acid) chelating resin was prepared by the reaction with poly(ethyl acrylate) crosslinked with divinylbenzene and hydrophilic crosslinking agent, and hydroxylamine. The hydrophilic crosslinking agents and diluent used in this article were ethylene glycol dimethacrylate or butanediol dimethacrylate, and 2,2,4-trimethyl pentane, respectively. The characterization of this type chelating resin was carried out by IR spectroscopy, density measurement, and scanning electron microscopy. Various metal binding properties such as extraction, kinetics, and selectivity were investigated with atomic absorption spectrometer and inductively coupled plasma spectrometer. Poly(hydroxamic acid) resins crosslinked with mixed crosslinking agents showed better metal extraction properties and faster adsorption rate than those crosslinked with divinylbenzene alone. And alkali treatment enhances the binding rate for metal ions because of the formation of other chelating ligands or micropores. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of poly(ethylene glycol)‐based thermo‐responsive polyurethane hydrogels for controlled drug release

The thermo‐responsiveness, swelling and mechanical properties of a series of novel poly(ester‐ether urethane) hydrogels have been investigated. These thermo‐sensitive hydrogels were obtained by combining hydrophobic biodegradable poly(ε‐caprolactone) diols and hydrophilic two‐, three‐ and four‐arm hydroxyl terminated poly(ethylene glycol) (PEG) of various molecular weights, using hexamethylene diisocyanate, dichloroethane as solvent and a tin‐based catalyst. The use of multifunctional PEGs leads to the formation of covalent crosslinking points allowing an additional control of the swelling capability. Thus, it was found that tuning the hydrophilic/hydrophobic balance and the crosslinking degree by changing the composition, the swelling and the thermo‐responsive behavior of these hydrogels could be modulated. The obtained hydrogels showed a volume transition at around room temperature. Therefore, and taking into account their biocompatibility, these hydrogels show promising properties for biomedical applications, such as drug delivery. Thus, the loading and release of diltiazem hydrochloride, an antihypertensive drug used as model, were investigated. These new PEG polyurethane hydrogels were able to incorporate a high amount of drug providing a sustained release after an initial burst effect. Copyright © 2013 John Wiley & Sons, Ltd.     

Dynamic mechanical properties and swelling of UV‐photopolymerized anionic hydrogels

The tensile dynamic mechanical properties and weight degree of swelling for anionic 2‐hydroxyethyl methacrylate‐co‐acrylic acid hydrogels were observed. Fabrication parameters examined were UV‐photopolymerization exposure time, UV‐photopolymerization intensity, and weight percentage crosslinker. The environmental conditions tested were electrolyte compositions of 0.5 and 0.05 M potassium hydroxide under applied frequencies of 0.1, 1, or 10 Hz. The overall maximum and minimum storage modulus was 1.83 ± 0.18 MPa and 68.5 ± 7.2 kPa, respectively, loss modulus was 432 ± 63 and 7.67 ± 3.22 kPa, respectively, and weight degree of swelling was 14.27 ± 1.27 and 1.95 ± 0.33, respectively. The morphology of fabricated hydrogels was examined using scanning electron microscopy showing a range of porous structures over the fabrication and environmental conditions examined, accounting for the variation in mechanical properties. The properties examined are of interest to researchers fabricating, designing, or modeling active hydrogel‐based microfluidic components. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Polystyrene (1)/poly(butyl acrylate/amide type functional monomer) (2) two-stage emulsion polymers. Synthesis and thermomechanical properties of latex films

Polystyrene (PS) (1)/Poly (n-butyl acrylate (BA)/amide type functional monomer) (2) structured latex particles were prepared through emulsion polymerization varying the hydrophilicity of the functional monomer employed. The second-stage polymerization kinetics, the size and morphology of latex particles, and the location of the functional groups in the final latexes were studied, in order to relate them to the thermomechanical properties of films cast from these latexes. It has been shown that, as expected, increasing the hydrophobicity leads to a better homogeneity in the copolymer formed during the second-stage polymerization, while the more hydrophilic functional monomer partly homopolymerizes in a separate phase. However, the functionalization by all the monomers used in this work, prevents the PS seed particles to form a continuous skeleton (percolated network). Further heat treatments at 140°C do not lead to the formation of a continuous PS phase as for pure BA/pure PS two-stage particles. In addition, some thermally induced crosslinking effects are discussed in relation with the functional monomer location within the particles. © 1995 John Wiley & Sons, Inc.     

Synthesis and characterization of novel thermoresponsive‐co‐biodegradable hydrogels composed of N‐isopropylacrylamide,poly(L‐lactic acid), and dextran

A series of novel multifunctional hydrogels that combined the merits of both thermoresponsive and biodegradable polymeric materials were designed, synthesized, and characterized. The hydrogels were copolymeric networks composed of N‐isopropylacrylamide (NIPAAM) as a thermoresponsive component, poly(L‐lactic acid) (PLLA) as a hydrolytically degradable and hydrophobic component, and dextran as an enzymatically degradable and hydrophilic component. The chemical structures of the hydrogels were characterized by an attenuated total reflection–Fourier transform infrared spectroscopy (ATR–FTIR) technique. The hydrogels were thermoresponsive, showing a lower critical solution temperature (LCST) at approximately 32 °C, and their swelling properties strongly depended on temperature changes, the balance of the hydrophilic/hydrophobic components, and the degradation of the PLLA component. The degradation of the hydrogels caused by hydrolytic cleavage of ester bonds in the PLLA component was faster at 25 °C below the LCST than at 37 °C above the LCST, determined by the ATR–FTIR technique. Due to their multifunctional properties, the designed hydrogels show great potential for biomedical applications, including drug delivery and tissue engineering. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5054–5066, 2004     

Synthesis and characterization of a novel polymer electrolyte based on acrylonitrile/N-[4-(aminosulfonyl)phenyl]acrylamide copolymers

<正>Acrylonitrile/N-[4-(aminosulfonyl)phenyl]acrylamide(AN/ASPAA) copolymers were synthesized and used as a host of lithium ion conducting electrolytes.The composition,molecular weight and molecular weight distribution of AN/ASPAA copolymers were determined,and the influence of copolymer composition on the glass temperature of AN/ASPAA copolymers and the ion conductivity of electrolytes were investigated.The molecular weights of AN/ASPAA copolymers were lower than those of AN and ASPAA homopolymers due to the cross-termination reaction.The glass temperatures of AN/ASPAA copolymers increased as the molar fraction of ASPAA units in copolymers increased.The lithium ion conductivities of the polymer electrolytes increased initially as the molar fraction of ASPAA units in copolymers increased,and a maximum conductivity was achieved when the molar fraction of ASPAA in the copolymer was 16.8%.     

Preparation and characterization of a novel magnetized nanosphere as a carrier system for drug delivery using Plantago ovata Forssk. hydrogel combined with mefenamic acid as the drug model

The aim of the present study was to magnetize Plantago ovata Forssk. hydrogel and produce a nanosphere system to carrier mefenamic acid as the drug model. For this propose, P. ovata seeds hydrogel (POSH) was extracted and magnetized by Fe₃O₄ being functionalized using tetraethyl orthosilicate and trimethoxyvinysilane. Thereafter, mefenamic acid (MFA) was loaded on the carrier system. The final product, as the magnetic drug loaded nanosphere (Fe/POSH/MFA), was fully characterized through different techniques involving X-ray diffraction (XRD), scanning electron microscopy (SEM), vibrating-sample magnetometer (VSM), thermal gravimetric analysis (TGA), dynamic light scattering (DLS), and FT-IR spectroscopy. The results confirmed the successful production of the drug loaded nanosphere system with particles magnetization of 25 emu/g over a range size of 40–50 nm. However, the size distribution less than 100 nm was measured through DLS analysis. The hydrogel showed a pH sensitivity swelling behavior representing the best efficacy at pH 7.4. The efficiency of the drug encapsulation was found to be 64.35%. The drug releasing was studied using a dialysis bag at pH = 7.4. The highest in vitro drug releasing was found to be 57.3 ± 0.6% after 72 h, as well. The findings of the current report account for the potential use of P. ovata hydrogel as an effective delivery system for encapsulation of water insoluble basic drugs, e.g., MFA in a magnetized carrier system.