Swelling characteristics of thermo- sensitive poly[(2-diethylaminoethyl methacrylate)-co-(N,N-dimethylacrylamide)] porous hydrogels (original) (raw)
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Journal of Applied Polymer Science, 2009
Macroporous temperature-sensitive poly {N-[3-(dimethylaminopropyl)] methacrylamide} hydrogels were synthesized by free-radical crosslinking polymerization of the monomer N-[3-(dimethylaminopropyl)] methacrylamide and the crosslinker N,N 0-methylenebisacrylamide in aqueous solutions at 22 C. Poly(ethylene glycol) (PEG) with a molecular weight of 1000 g/mol was used as the pore-forming agent during the polymerization reaction. The concentration of PEG in the polymerization solutions was varied between 0 and 18 wt %, whereas the crosslinker (N,N 0-methylenebisacrylamide) concentration was fixed at 2 wt % (with respect to the monomer). The effects of the PEG concentration on the thermo-induced phase-transition behavior and the chemical structure, interior morphology, and swelling/deswelling kinetics were investigated. Normal-type hydrogels were also prepared under the same conditions without PEG. An interesting feature of the swelling behavior of both the normal-type and macroporous hydrogels was the reentrant phase transition, in which the hydrogels collapsed once and reswelled as the temperature was continuously increased. Scanning electron micrographs revealed that the interior network structure of the hydrogels prepared in PEG solutions became more porous with an increase in the PEG concentration in the polymerization solution. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved responsive rate to external temperature changes during the deswelling and swelling processes. V
Macromolecular Chemistry and Physics, 2003
A systematic comparison of the effect of architectural modifications to the network structure on the internal microstructure of N‐isopropylacrylamide (NIPA) based hydrogels showed that the addition of a second component to the network significantly increased the proportion of macropores in the network. The second components considered were short poly(N‐isopropylacrylamide) (PNIPAM) chains grafted to the network backbone, high‐molecular‐weight polyacrylamide (PAM) chains, or microsphere particles of PNIPAM. Structures are proposed for each of the modified gel networks taking into account the new structural information. Through a combination of the pore size and network structure data reported here, and with the shrinking data obtained previously, shrinking mechanisms are proposed for each of the modified network structures. In all cases, the enhanced shrinking rates were directly caused by the presence of the second component, which acted as nuclei for shrinking (graft‐PNIPAM and PNI...
Industrial & Engineering Chemistry Research, 2011
Homopolymer of N,N-dimethylaminoethyl methacrylate sulfate (DMAEMASA) and its copolymer with N,Ndimethylacrylamide (DMAm) [P(DMAEMASA-co-DMAm)] were synthesized in the presence and absence of pore-forming agents NaHCO 3 , poly(ethylene glycol) 2000 (PEG), and sucrose (SUC). The polymers were characterized by equilibrium swelling measurements (ESVs) in distilled water (20À60°C) and buffer solutions (I = 0.1 M, pH = 2.2À10.0, 20°C), FTIR, DSC, and SEM methods. The presence of DMAm in monomer feed and the use of pore-forming agents during the polymerization enhanced the swelling of polymers. ESVs of both porous and nonporous PDMAEMASA and P(DMAEMASA-co-DMAm) gels decreased with pH, and displayed a phase transition at pH = 5. Among the pore-formers, NaHCO 3 made the highest contribution to the swelling of polymers, but poly(ethylene glycol) and sucrose slightly affected the swelling values of gels. While glass transition temperature (T g) of nonporous DMAEMASA homopolymer was determined to be 168.4°C, T g s of nonporous copolymer with 20-and 40-mol % DMAm were found to be 154.5 and 147.8°C, respectively. Pore-formers decreased the T g of homopolymer in the order NaHCO 3 < PEG < SUC. In case of copolymers, NaHCO 3 and PEG had nearly no effect on T g s, but sucrose led to approximately 7°C decrease in T g s of copolymers.
Poly(N-isopropylacrylamide) (PNIPAM) hydrogels were prepared by free-radical polymerization in different ethanol-water mixtures. A scanning electron microscopy study revealed that the resulting hydrogels were macroporous. The swelling ratios of the resultant hydrogels in water at 20 C followed this order: X 0.34 % X 0.68 > X 0.48 > X 0.09 > X 0.04 > X 0 , where X a denotes a gel prepared in an ethanol-water solvent mixture with an ethanol molar fraction of a. Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with increasing temperature. The complete collapse of the PNIPAM chain of all of these gels occurred at about 38 C, whereas the same was observed at about 35 C for the conventional gel prepared in water. The swelling ratio values of all of the PNIPAM gels with different molar fractions of ethanol at 20 C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X 0.34 > X 0.48 > X 0.68 > X 0.09 > X 0.04 > X 0 . The reswelling rates of these hydrogels decreased in the following order: X 0 > X 0.04 % X 0.48 > X 0.09 % X 0.68 > X 0.34 . The freeze-drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels.
The development of bulk, three-dimensional (3D), macroporous polymers with high permeability, large surface area and large volume is highly desirable for a range of applications in the biomedical, biotechnological and environmental areas. The experimental techniques currently used are limited to the production of small size and volume cryogel material. In this work we propose a novel, versatile, simple and reproducible method for the synthesis of large volume porous polymer hydrogels by cryogelation. By controlling the freezing process of the reagent/polymer solution, large-scale 3D macroporous gels with wide interconnected pores (up to 200 μm in diameter) and large accessible surface area have been synthesized. For the first time, macroporous gels (of up to 400 ml bulk volume) with controlled porous structure were manufactured, with potential for scale up to much larger gel dimensions. This method can be used for production of novel 3D multi-component macroporous composite materials with a uniform distribution of embedded particles. The proposed method provides better control of freezing conditions and thus overcomes existing drawbacks limiting production of large gel-based devices and matrices. The proposed method could serve as a new design concept for functional 3D macroporous gels and composites preparation for biomedical, biotechnological and environmental applications. Macroporous polymer gels have been used in a wide range of applications, including tissue engineering, as cell scaffolds, in bioreactors, materials for biological and chemical separations, and as adsorbents in biomedi-cal and environmental applications. Porosity in gels can be created by different approaches: phase separation 1 using so-called porogens (chemical additives that generate pores), lyophilization 2,3 , via foam formation, and via cryogelation 4,5. The latter method is one of the most versatile techniques used in the last few decades for shaping the porous structure of polymer gels 5–7. The technology is simple; it commonly requires only one cycle of freezing-defrosting of the reagent/polymer solution, and allows production of materials of varying morphology, mechanical properties and permeability 8,9. The technique is more environmentally friendly than alternative techniques as the most common solvent used is water, and there is no requirement to use organic solvents for removing the pore forming template. The porous polymer is formed in semi-frozen conditions when the major part of the solvent is solidified, forming solvent crystals at temperatures below the normal freezing point, with polymeri-zation taking place in the intercrystalline channels containing unfrozen solution. Increasing the temperature after completion of polymerization leads to defrosting of the solvent crystals and formation of interconnected voids (macropores) in the polymer structure filled with the solvent. Particular interest has arisen due to the high per-meability (and consequently low flow resistance) of gels prepared from aqueous solutions and their ability to filter micro-and macro-particles without clogging and pore blockage 10. This opens the opportunity to design devices for cell and bioparticles separation 10–13 , direct blood perfusion 14 , tissue engineering 15–20 , water treatment 21–23 and
Synthesis of porous hydrogel structures by polymerizing the continuous phase of a microemulsion
Polymer International, 1995
A series of microemulsions have been formulated, with 2-hydroxyethyl methacrylate (HEMA) or HEMA/water/propanol mixtures as the continuous phase and methylcyclohexane as the discontinuous phase. The effect of surfactant type was investigated with the utilization of both anionic and nonionic surfactants. The microemulsion continuous phase was polymerized by UV radiation and a thermal post-cure. The resultant polymers were extracted to remove the discontinuous phase and the surfactant. On swelling, the majority of the polymers became opaque, although transparent PHEMA hydrogels were synthesized with an improved equilibrium water content (EWC). The cause of opacity was shown by field emission scanning electron microscopy (FESEM). The breakdown in the microemulsion on polymerization is caused by unfavourable interactions between the PHEMA and the stabilizing surfactants causing agglomerization of the discontinuous phase. All the hydrogels were found to have higher water retention than PHEMA, with EWCs of up to 70%. The modified polymers also demonstrated an increased rate of water diffusion into the matrix. A preliminary study of oxygen permeability revealed that a significant improvement had been made over standard PHEMA membranes. The porous structure of the PHEMA gels has been shown to be dependent on the type of surfactant used during synthesis.
Macroporous Poly(Acrylamide) Hydrogels: Swelling and Shrinking Behaviors
Journal of Macromolecular Science, Part A, 2006
Macroporous poly(acrylamide) hydrogels have been synthesized by using poly(ethylene glycol) (PEG) with three different molecular weights as the pore-forming agent. Scanning electron microscope graphs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights of PEG during the polymerization reaction. The swelling ratios of the PEG-modified hydrogels were much higher than those for the same type of hydrogel prepared via conventional method. However, the swelling/deswelling ratios of the PEG-modified hydrogels were affected slightly by the change in the amount of the PEG. Scanning electron microscopy experiments, together with swelling ratio studies, reveal that the PEG-modified hydrogels are characterized by an open structure with more pores and higher swelling ratio, but lower mechanical strength, compared the conventional hydrogel. PAAm has potential applications in controlled release of macromolecular active agents.
Journal of Applied Polymer Science, 2009
Macroporous temperature-sensitive poly {N-[3-(dimethylaminopropyl)] methacrylamide} hydrogels were synthesized by free-radical crosslinking polymerization of the monomer N-[3-(dimethylaminopropyl)] methacrylamide and the crosslinker N,N 0 -methylenebisacrylamide in aqueous solutions at 22 C. Poly(ethylene glycol) (PEG) with a molecular weight of 1000 g/mol was used as the pore-forming agent during the polymerization reaction. The concentration of PEG in the polymerization solutions was varied between 0 and 18 wt %, whereas the crosslinker (N,N 0 -methylenebisacrylamide) concentration was fixed at 2 wt % (with respect to the monomer). The effects of the PEG concentration on the thermo-induced phase-transition behavior and the chemical structure, interior morphology, and swelling/deswelling kinetics were investigated. Normal-type hydrogels were also prepared under the same conditions without PEG. An interesting feature of the swelling behavior of both the normal-type and macroporous hydrogels was the reentrant phase transition, in which the hydrogels collapsed once and reswelled as the temperature was continuously increased. Scanning electron micrographs revealed that the interior network structure of the hydrogels prepared in PEG solutions became more porous with an increase in the PEG concentration in the polymerization solution. This more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved responsive rate to external temperature changes during the deswelling and swelling processes.
Polymer International, 2006
Macroporous poly(N-isopropylacrylamide) (PNIPA) hydrogels were synthesized by free-radical crosslinking polymerization in aqueous solution from N-isopropylacrylamide monomer and N,N-methylenebis (acrylamide) crosslinker using poly(ethylene glycol) (PEG) with three different number-average molecular weights of 300, 600 and 1000 g mol −1 as the pore-forming agent. The influence of the molecular weight and amount of PEG pore-forming agent on the swelling ratio and network parameters such as polymer-solvent interaction parameter (χ) and crosslinking density (ν E ) of the hydrogels is reported and discussed. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying different molecular weights and compositions of PEG during polymerization. At a temperature below the volume phase transition temperature, the macroporous hydrogels absorbed larger amounts of water compared to that of conventional PNIPA hydrogels, and showed higher equilibrated swelling ratios in aqueous medium. Particularly, the unique macroporous structure provides numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to external temperature changes during the swelling and deswelling process. These macroporous PNIPA hydrogels may be useful for potential applications in controlled release of macromolecular active agents.
Journal of Applied Polymer Science, 2011
In this work, we investigated the design and fabrication of porous polyacrylamide hydrogels via a thermal reverse-casting technique. The porous hydrogels were prepared by the free-radical crosslinking polymerization of the monomer solution within the space of an agarose gel, which after the setting of the chemical gel, was removed to allow for the formation of an interconnected porosity pathway. Two different agarose/monomer solution ratios were selected to modulate the porosity of the hydrogels, and the as-obtained samples were characterized in terms of their chemical structure, morphology, thermal properties, and swelling behavior in different ionic strength solutions. The results of this study demonstrate that the reverse-casting process enhanced the solventretaining capability of the hydrogels and that their swelling ratio increased with increasing concentration of the agarose solution in the initial formulation. All of these results finally demonstrate that the pore structure features played a key role in defining the swelling behavior of the hydrogels.