p-Nitrophenol permeability and temperature characteristics of an acryloyl-L-proline methyl ester-based porous gel membrane

Thermoresponsive porous gel membranes were synthesized by a simultaneously occurring process consisting of radiation-induced polymerization and crosslinking in aqueous solutions at various concentrations of acryloyl-L -proline methyl ester(A-ProOMe) without a crosslinker. Permeation of p-nitrophenol (PNP) through a thermoresponsive porous gel membrane obtained at a monomer concentration of 80% (w/w) drastically reduced around 14°C, the lower critical solution temperature (LCST) of linear poly(A-ProOMe) in water, from 0.60 × 10⁻³ cm/min at 10°C to no permeation at 18°C, accompanied by changes in both size and shape of pores associated with gel shrinkage. Moreover, it was found that porous gel membranes with a porosity of approximately 60% had a greater PNP permeability constant through porous gel membranes with mutually connected pores obtained at a monomer concentration of 50% (w/w) than individually supported pores obtained at a monomer concentration of 70% (w/w). © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1495–1500, 1998     

A viscosity-tunable polymer for DNA separation by microchip electrophoresis

A thermo-responsive separation matrix, consisting of Pluronic F127 tri-block copolymers of poly(ethylene oxide) and poly(propylene oxide), was used to separate DNA fragments by microchip electrophoresis. At low temperature, the polymer matrix was low in viscosity and allowed rapid loading into a microchannel under low pressure. With increasing temperatures above 25°C, the Pluronic F127 solution forms a liquid crystalline phase consisting of spherical micelles with diameters of 17–19 nm. The solution can be used to separate DNA fragments from 100 bp to 1500 bp on poly(methyl methacrylate) (PMMA) chips. This temperature-sensitive and viscosity-tunable polymer provided excellent resolution over a wide range of DNA sizes. Separation is based on a different mechanism compared with conventional matrices such as methylcellulose. To illustrate the separation mechanism of DNA in a Pluronic F127 solution, DNA molecular imaging was performed by fluorescence microscopy with F127 polymer as the separation matrix in microchip electrophoresis. Figure Temperature dependence of the viscosity of 20% w/w Pluronic F127 solution in 1xTBE buffer. Dotted approximates resultant curve.     

Crosslinked poly(N-isopropylacrylamide) gel for electrophoretic separation and recovery of substances

Crosslinked poly(N-isopropylacrylamide) gel was tested on the feasibility for a preparative electrophoretic matrix. Horse heart myoglobin and bovine hemoglobin were well separated on the gel matrix electrophoretically by molecular sieving effect of the gel network. Relative mobilities of those proteins in the gel were larger than those in a crosslinked polyacrylamide gel of the same polymer concentration. After the separation, the protein-containing portion of the gel underwent swelling at 4°C and deswelling at 37°C, alternatively. As a result of the deswelling, each protein was recovered in a discharged solution out of the gel at almost 100% yield.     

Effect of PLGA block molecular weight on gelling temperature of PLGA‐PEG‐PLGA thermoresponsive copolymers

Thermoresponsive, biodegradable polymeric hydrogel networks are used widely in medicinal applications. Poly(d ,l ‐lactic acid‐co‐glycolic acid)‐b‐poly(ethylene glycol)‐b‐poly(d ,l ‐lactic acid‐co‐glycolic acid) (PLGA‐PEG‐PLGA) triblock copolymers exhibit a sol–gel transition upon heating. The effect of PLGA block and PEG chain molecular weights (MWs) on the gelling temperature of polymer aqueous solution (20% w/w) is described. All polymer solutions convert into a hard gel within 2 °C of the gelling temperature. The release properties of the gels were displayed using paracetamol as a representative drug. A linear relation is described between the gelling temperature and PLGA block MW. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 35–39     

Characterizing the impact of thermal gels on isotachophoresis in microfluidic devices

Thermally reversible Pluronic gels have been employed as separation matrices in microfluidic devices in the analysis of biological macromolecules. The phase of these gels can be tuned between liquid and solid states using temperature to vary fluidic resistance and alter peak resolution. Although separations in thermal gels have been characterized, their effect on isotachophoresis has not. This study used fluorescein as a model analyte to evaluate isotachophoretic preconcentration as a function of thermal polymer concentration and temperature. Results demonstrated that increasing polymer concentration in microfluidic channels increased the apparent analyte concentration. A critical minimum of 10% (w/v) Pluronic was required to achieve efficient preconcentration with maximum focusing occurring in 20 and 25% polymer gels. Temperature of the thermal gel also impacted analyte focusing. Most efficient focusing was achieved at 25°C with diminishing analyte accumulation at higher and lower temperatures. Under optimal conditions, isotachophoretic preconcentration increased an additional threefold simply by including thermal gels in the system. This approach can be readily implemented in other applications to increase detection sensitivity and measure low-concentration analytes within simple microfluidic devices.     

Gelation in the Copolymerization of Diallyldimethylammonium Chloride with Acrylamide

Diallyldimethylammonium chloride (DADMAC) was free-radical copolymerized with acrylamide (AA) in water at a total monomer concentration of 4 mol/L and 40°C with different monomer feed compositions. Gelation occurred only for 20/80 DADMAC/AA monomer feed although crosslinking was observed for all monomer feed compositions. The gel point was at 51% conversion, and the swelling ratios of the resulting gels were quite high, from 1400 to 700. Addition of 2‐propanol as a chain‐transfer reagent reduced crosslinking and prevented gelation. These results are mechanistically discussed in connection with the cyclopolymerizability of DADMAC, and significant allylic hydrogen abstraction by the growing polymer radical characteristic of allyl polymerization is proposed.     

Complexes of polyelectrolyte hydrogels with organic dyes: Effect of charge density on the complex stability and intragel dye aggregation

The swelling behavior of polyelectrolyte gels based on poly(diallyldimethylammonium chloride) (copolymers of diallyldimethylammonium chloride and acrylamide with the variable composition) and poly(methacrylic acid, sodium salt) in the presence of organic water soluble dyes (alizarin, naphthol blue black, rhodamine) was studied. The collapse of the polyelectrolyte gels in the presence of oppositely charged dyes together with the effective absorption of dyes was observed. The shrinking degree and the dye absorption by the gel depend on the charges of the polymer network and the dye, and also on the dye concentration. Stability of the gel–dye complexes in a salt solution of NaCl and Al₂(SO₄)₃ was studied. It was shown that the complex stability in the salt solution depends on the charge density of the polymer chains forming the gel. The increase of charge density of polymer generally leads to the enhancement of the complex stability. For the systems with the fraction of charged poly(diallyldimethylammonium chloride) monomer units above 0.5 the release of alizarin to the external solution of Al₂(SO₄)₃ reservoir is practically completely suppressed. The obtained results show that oppositely charged dyes are generally from stable complexes with polyelectrolyte gels. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1209–1217, 1999     

Degradation of Poly(2-hydroxyethyl methacrylate) Obtained by Radiation in Aqueous Solution

The degradation of poly(hydroxyethyl methacrylate), PHEMA obtained by γ -radiation induced polymerization of HEMA in aqueous solution, was studied. The polymer was a gel type and insoluble in common organic solvents. The DSC thermogram of the polymer gave a Tg value at 88.2°C and an endothermic peak showed further polymerization or crosslinking at 110–160°C. The degradation observed in TGA was a depolymerization type. However, the FT-IR of TGA fragments showed no monomer, which was degraded further. The degradation of monomer was studied by the GC-MS method. Similar results were also observed.     

Interaction of non-ionic hydrogels with weak aromatic acids

Measurements are reported of the swelling behaviour at 20°C of poly (N isopropylacrylamide) (PNIPA) gels in aqueous solutions of two weak aromatic acids, phenol and resorcinol. For solute concentrations below 45 mmol/l the uptake of these solutions is similar. Due to selective solvation phenol exhibits an excess equilibrium concentration inside the gel of 5% over that in the surrounding bath, while for resorcinol, the excess is found to be 12%. At 50 mmol/l solute concentration, both systems display a volume transition accompanied by expulsion of the solvent. The solubility limits in water of these aromatic compounds, which are significantly different from each other (870 mmol/l and 9080 mmol/l respectively), are far above this critical concentration. In the collapsed condition the expelled liquid spreads on the surface of the phenol treated gel, while an ordered arrangement of separate droplets is generated in the case of resorcinol. In the latter case an acute contact angle was observed. It is also shown by acid-base titration that the PNIPA/water system may exhibit a slight ion exchanging character.     

Aromatic polyamides. IV. A novel synthesis of sulfonated poly(para-phenyleneterephthalamide): Polymerization of terephthalic acid and para-phenylenediamine in sulfur trioxide

A novel polyamide condensation reaction of aromatic diamines (usually as strong inorganic acid salts) and aromatic diacids in SO₃ has been discovered. para-Phenylenediamine was polymerized with terephthalic acid in SO₃ at 20–47% polymer concentration to form highly anisotropic (liquid crystalline) sulfonated poly(p-phenyleneterephthalamide) (SPT) solutions (dopes) with inherent viscosities as high as 1.6. Sulfonation of the aromatic diamine ring was a major side reaction. The effects of reaction variables such as temperature, time, monomer concentration, stoichiometry, and solvent acidity on molecular weight were studied. The dopes were spun to fiber, but tensile properties were limited by coagulation problems associated with hydrophilicity of the highly sulfonated polymer. Thermogravimetric analysis of SPT at 20°C/min showed weight loss only above 450°C.     

Reduced viscosity polymer matrices for microchip electrophoresis of double-stranded DNA

On a polymethylmethacrylate (PMMA) microchip, double-stranded DNA fragments with a wide size range from 50 bp to 20 kbp were separated by two polymer solutions. One was a hydroxypropylmethylcellulose-4000 (HPMC-4000) solution of 1.3% (w/v) to separate fragments below 590 bp, and another was a mixed four molecular weight poly(ethylene oxide) solution at a total concentration of 0.1% to separate fragments above 520 bp. The widths at half height (wh) of the fragments had a good relationship with their migration times (tR) in both polymer solutions. Such a relationship was suitable for obtaining the wh values of unresolved peaks, calculating the resolution of two adjacent fragments, and optimizing microchip separation matrices. Based on the relativity, a low viscosity medium containing 2% HPMC-50 and 8% glucose was optimized for high-performance separation of a phiX174 HaeIII restriction fragment digest.     

Synthesis and characterization of electroactive epoxy‐based interpenetrating polymer network gel

Epoxy/poly(N‐isopropylacrylamide) interpenetrating polymer network gels were prepared by varying the excess amine content in the matrix (0.4–0.6 equivalent). All the samples were characterized for mechanical properties and swelling in distilled water. The topography of polymer network was characterized by atomic force microscopy. The 0.5 equiv. excess amine sample exhibited optimum properties. Studies on swelling at different pH and electroactivity in different aqueous solution were performed. The bending angle observed during first 1 min was 1–5° at 3–10 V and a maximum of 25° in 5 min at 20 V for 0.5 equiv. excess amine in NaCl solution. Copyright © 2011 John Wiley & Sons, Ltd.     

Chemically Crosslinked pH- and Temperature-Sensitive (N-isopropylacrylamide-co-1-vinyl-2-pyrrolidone) Based on New Crosslinker: I. Swelling Behavior

Novel pH- and temperature-sensitive polymer matrices based on N-isopropylacrylamide have been developed. The hydrogels were prepared by bulk radical polymerization of N-isopropylacrylamide and 1-vinyl-2-pyrrolidinone in appropriate amounts of distilled water using different mol% of traditional N,N-methylene bisacrylamide (MBA) and the new synthesized N,N,N-tris acryloyl melamine (MAAm) crosslinkers. Lower critical solution transition temperatures (LCST) were measured by differential scanning calorimetry. The synthesized hydrogels have LCST lower than 40°C. 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 crosslinked NIPAAm/VP with MAAm hydrogels exhibited more rapid deswelling rate than NIPAAm/VP hydrogels crosslinked with MBA in pure water in response to abrupt temperature changes from 20°C to 50°C.     

Preparative electrochromatography of proteins in various types of porous media

The performance of commercial and enzymatically modified size-exclusion (SE) gels in electrochromatography was compared for preparative protein separations. Dextran and agarose-based SE gels were subjected to enzymatic digestion under mild conditions. This treatment partially hydrolyzed the gel matrix modifying its pore size distribution. Enzymatic treatment of agarose-based SE gels was found to increase the resolution of the separation. Successful separation of preparative amounts of the A and B forms of beta-lactoglobulin (difference in electrophoretic mobility of 8.5%) was achieved with a high degree of purity using agarose-based SE gels. The four major whey proteins, beta-lactoglobulin, alpha-lactalbumin, BSA and immunoglobulins, were purified from an acid whey preparation. The degree of retention of a protein in electrochromatography followed their free-solution electrophoretic mobility (mu) when the protein was able to enter the gel pores and the ratio of diffusion/mu when the protein was excluded.     

Preparation of polyamides via the phosphorylation reaction. X. A study of higashi reaction conditions

We report a study of the conditions of the phosphorylation reaction for the preparation of aromatic polyamides using the Higashi reaction medium. For poly(p-phenylene terephthalamide) (PPD-T), the optimum conditions are: reaction temperature, 115°C; monomer concentration, C = 0.083 mol/L; and ratio of triphenyl phosphite (TPP) to monomer, 2.0. These optimum conditions produce PPD-T having η_inh = 6.2 dL/g. At temperatures of 120°C and above PPD-T precipitates from the reaction mixture, leading to lower molecular weights. At lower temperatures the reaction mixture gels, and the gel time decreases with increasing reaction temperature. However, polycondensation continues in the gel state. Monomer concentrations C = 0.10 mol/L and above produce precipitation and yield polyamides of lower molecular weight. For the preparation of poly(p-benzamide) (PBA), the optimum ratio of TPP to monomer is 0.6 for either p- aminobenzoic acid or N-4-(4′-aminobenzamido)benzoic acid. In the former case the inherent viscosity of polymer prepared at 115°C showed little dependence upon the concentration of the monomer. The highest value, η_inh = 1.8 dL/g, was obtained with C = 0.40 mol/L and a TPP/monomer ratio of 0.6. However, for the same TPP/monomer ratio, the monomer containing a preformed amide linkage, N-4-(4′-aminobenzamido)benzoic acid, gave PBA with η_inh = 4.6 dL/g when the monomer concentration is 0.33 mol/L. This is the highest value reported for PBA using the phosphorylation reaction. In A?A + B?B polycondensation, examples in which one of the monomers contained one or two preformed amide linkages produced polyamides having η_inh = 7.8 and 8.9 dL/g, respectively.     

Rapid crystallization and thermoreversible gelation of poly(ethylene terephthalate) in polymer/oligomer binary system

Poly(ethylene terephthalate) (PET) was rapidly crystallized through thermoreversible gelation in a liquid ethylene glycol oligomer or in epoxy resin. The solutions formed gel rapidly on cooling. Polarized light microscopy and small-angle light scattering showed that these gels contain large, regular PET spherulites. The gels may be formed by two consecutive processes: the phase separation and crystallization, and gelation by formation of a three-dimensional PET network in the oligomer solvents, where the nodes of the network are PET spherulites. The crystallinity of PET recovered from polymer/oligomer gels is near 72% measured by wide-angle X-ray diffraction method, which is about 20% higher than PET samples crystallized by solution crystallization in small molecule solvent, high temperature annealing, and stretching techniques. It takes only a few minutes to form the highly crystalline phase PET in the PET/oligomer system, and the crystallinity of the dried gel is independent of the concentration of the original solution. Excimer-fluoresence and Raman spectroscopic studies indicated that PET recovered from the gels are in an ordered state with few chain entanglements. The entanglement density of the recovered PET recovered from a 20 wt % solution in ethylene glycol oligomer is as low as that of freeze-extracted PET from a 0.5 wt % solution in phenol. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1219–1225, 1998     

Real space structure of opaque gel

The structure of the opaque poly(acrylamide) gels is studied by using a confocal laser scanning microscope. The polymer network of the gel consists of the fractal aggregate of the colloidal particles in the higher concentration region of the cross-linker. The diameter of the colloidal particle, which formed in the gel, increases from 180 to 420 nm with an increase of the concentration of cross-linker. On the other hand, the fractal dimensions of the aggregate remain constant, ranging from 1.5 to 1.7. The densities of the particle are calculated to be 0.7 and 1.2 x 103 kg/m3, which are >10 times larger than the average density of the polymer network of the gel. The results indicate that the monomer and the cross-linker are densely cross-linked into the particles.     

Superfast Responsive Ionic Hydrogels: Effect of the Monomer Concentration

A series of strong polyelectrolyte gels were prepared in aqueous solution, using the sodium salt of 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS) as the monomer and N,N'‐methylene(bis)acrylamide (BAAm) as a crosslinker. The gels were both prepared below (?22°C) and above (25°C) the bulk freezing temperature of the water, producing cryogels and hydrogels, respectively. The crosslinker (BAAm) content was set at 17 mol%, while the initial monomer concentration C_o was varied over a wide range. It was found that, at ?22°C, a macroscopic network starts to form at an initial monomer concentration of as low as 0.1 w/v%. In contrast to the conventional hydrogels formed at 25°C, the cryogels have a discontinuous morphology consisting of polyhedral pores of sizes 10⁰–10² μm. The cryogels exhibit superfast swelling properties, as well as reversible swelling–deswelling cycles in water and acetone. An increase in the initial monomer concentration from 2.5 to 10% further increases the response rate of the cryogels due to the simultaneous increase of the porosity of the networks.     

EFFECT OF GAMMA RAYS IN THE PREPARATION OF POLYMER AND HYDROGEL FROM ACRYLAMIDE MONOMER

The formation of polymer and hydrogel from aqueous solutions having 20, 30 and 40% concentrations ofacrylamide monomer by γ-ray irradiation processing in the dose range 0.06-30 kGy using a Co-60 source and theircharacterization have been observed. Polymer conversion and gel fraction are found to depend on radiation doses. Polymerconversion increases with the increase of dose, depending on the solution concentration, where maximum conversion isachieved at 0.18, 0.16 and 0.10 kGy for 20%, 30% and 40% concentrations, respectively. On the other hand, gel fractionincreases with dose from the gel point (0.12 kGy) for all concentrations, where 100% conversion of gel occurs at doses≥5 kGy. Tensile strength, viscosity and molecular weight (M_w) of polymer samples increase with both the dose and theconcentration, showing a high value of M_w up to≈10~8. Swelling of hydrogels under water with respect to time varies due tothe variation of cross-linking density formed in the gels and the maximum swelling mainly occurs within 24 h. A remarkable change of surface morphology reveals characteristic features of monomer, polymer and hydrogel films.     

Feasibility of the recovery of uranium from alkaline waste by amidoximated grafted polypropylene polymer matrix

The amidoximated grafted polypropylene polymer matrix was prepared by post irradiation grafting of acrylonitrile (AN) onto thermally bonded non-woven matrix of poly(propylene) sheet using electron beams. This precursor polymer was reacted with hydroxylamine to convert AN to poly(acrylamidoxime) (AO) groups, and conditioned by treating them with 2.5 % KOH at 80 °C for 1 h. The polymer matrix was having the degree of AN grafting ~106 wt% and its subsequent conversion to AO groups ~70 %. The water uptake capacity of AO polymer matrix were found to be 100 ± 5 % (w/w). Quantitative recovery of uranium from alkaline waste (ammonium diuranate supernatant) solution was achieved by this polymer matrix. The other radionuclides present in the waste solution were not extracted by the polymer matrix. For all other radionuclides, the uptake was found to be <6 %.