Swelling Ratio Values Research Articles

Swelling-induced structural changes and microparticle uptake of gelatin gels probed by NMR and CLSM

Gelatin gels are increasingly involved in many industrial applications due to several advantages including cost efficiency and biocompatibility. Generally, their production requires the use of aqueous solvents, which cause significant swelling, due to the ability of solvent molecules to penetrate through the gel microstructure and increase its volume. Since swelling mechanisms and their effect on the gel structure are not fully understood, further investigations are required. In this work, we combine macroscopic measurements of the swelling ratio (SR) with Nuclear Magnetic Resonance (NMR) and Confocal Laser Scanning Microscopy (CLSM) to investigate changes in the gelatin structure as a function of both polymer concentration and swelling time. SR values increase as a function of time until a maximum is reached and then show a slight drop for all the gelatin concentrations after 24 h swelling time, probably due to a network relaxation process. NMR allows determination of mass transport and molecular dynamics of water inside the gelatin pores, while CLSM is used to visualize the penetration of tracers (polystyrene microbeads) with a diameter much larger than the gel pores. Structural parameters, such as average pore size and tortuosity, are estimated. In particular, the pore size decreases for higher polymer concentration and increases during swelling, until reaching a maximum, and then dropping at longer times. The penetration of tracers provides evidence of the heterogeneity of the gel structure and shows that single microcarriers can be loaded in gelatin gels upon swelling.

In vitro release of metformin hydrochloride from sodium alginate/polyvinyl alcohol hydrogels

Hydrogels, based on polysaccharides have found a number of applications as drug delivery carriers. In this work, hydrogels of full characterized sodium alginate (Mn 87,400g/mol) and commercial poly(vinyl alcohol) (PVA) sensitive to pH and temperature stimuli were obtained using a simple, controlled, green, low cost method based on freeze-thaw cycles. Stable hydrogels of sodium alginate/PVA with 0.5:1.5 and 1.0:1.0w/v concentrations showed very good swelling ratio values in distilled water (14 and 20g/g, respectively). Encapsulation and release of metformin hydrochloride in hydrogels of 1.0:1.0w/v sodium alginate/PVA was followed by UV spectroscopy. The hydrogel released a very low amount of metformin hydrochloride at pH 1.2; the highest release value (55%) was obtained after 6h at pH 8.0. Also, the release of metformin hydrochloride was studied by 1H NMR spectroscopy, the temporal evolution of methyl group signals of metformin showed 30% of drug release after 3h.

Effect of the composition of methanol−water mixtures on tacticity of poly(N‐ethylacrylamide) gel

ABSTRACTTwo series of macroporous poly(N‐ethylacrylamide) (PNEAM) gels are synthesized in different composition of methanol–water mixtures (xm = 0, 0.06, 0.13, 0.21, 0.31, and 0.43; where xm = mole fraction of methanol) in presence as well as in the absence of 0.1M Y(OTf)3 Lewis acid as additive. The gels synthesized in the absence of Lewis acid are atactic and in the presence of the same are isotactic. Synthesis of the corresponding linear PNEAM homopolymers shows that, the isotacticity (meso dyad, %) of the resulted polymers increases for the gels prepared in the presence of Lewis acid (LA) and remains constant for the gel prepared in the absence of LA, respectively, with the increase in the concentration of the synthesis solvent methanol. SEM micrographs reveal that, the hydrogels synthesized in the presence of LA are more porous than the gels prepared in the absence of LA. Swelling ratio of all the hydrogels decreases with the increase in the temperature and LA gels show higher swelling ratio values than non LA gels (NLA). Deswelling rate of the hydrogels prepared in methanol–water mixture in presence of LA is faster than the hydrogels prepared in absence of LA. Moreover, reswelling rate increases with increase in the isotacticity of the PNEAM segment in the gel. All these results have been explained on the basis of the formation of highly porous hydrogels with higher isotactic PNEAM chain segment in the presence of LA in methanol–water mixtures. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41668.

Efficient sorption of Cu(2+) by composite chelating sorbents based on potato starch-graft-polyamidoxime embedded in chitosan beads.

Ionic composites based on cross-linked chitosan (CS) as matrix and poly(amidoxime) grafted on potato starch (AOX) as entrapped chelating resin were prepared as beads, for the first time in this work, by two strategies: (1) thorough mixing of previously prepared AOX in the CS solution followed by the bead formation and (2) thorough mixing of the potato starch-g-poly(acrylonitrile) (PS-g-PAN) copolymer in the initial CS solution, followed by bead formation, the amidoximation of the nitrile groups taking place inside the beads. Ionotropic gelation in tripolyphosphate was used to obtain the composite beads, and in situ covalent cross-linking by epichlorohydrin was carried out to stabilize the beads in the acidic pH range. Fourier transform infrared spectroscopy and the swelling ratio values in the acidic pH range confirmed the influence of the synthesis strategy on the structure of the CS/AOX composites. Scanning electron microscopy was employed to reveal the morphology of the novel composites, both before and after their loading with Cu(2+). The binding capacity of Cu(2+) ions as a function of sorbent composition, synthesis strategy, pH, sorbent dose, contact time, initial concentration of Cu(2+), and temperature was examined in batch mode. The main difference between the composites prepared with the two strategies consisted of the higher sorption capacity and the much faster settlement of the equilibrium sorption for the composite prepared by the in situ amidoximation of PS-g-PAN. The Langmuir, Freundlich, Temkin, Dubinin-Radushkevich, and Sips isotherms were applied to fit the sorption equilibrium data. The maximum equilibrium sorption capacity, qm, evaluated by the Langmuir model at 25 °C was 133.15 mg Cu(2+)/g for the CS/AOX composite beads prepared with the first strategy and 238.14 mg Cu(2+)/g for the CS/AOX composite beads prepared with the second strategy, at the same AOX content. The pseudo-second order kinetic model well fitted the sorption kinetics data, supporting chemisorption as the mechanism of interaction between the chelating composites and the Cu(2+) ions. The CS/AOX composite sorbents could be reused up to five sorption/desorption cycles with no significant decrease in Cu(2+) sorption capacity.

Arabinoxylan microspheres: structural and textural characteristics.

The aim of this research was to study the structural and textural characteristics of maize bran arabinoxylan (MBAX) microspheres. The laccase-induced cross-linking process was monitored by storage (G') and loss (G'') moduli changes in a 4% (w/v) MBAX solution. The G' and G'' values at the plateau region were 215 and 4 Pa, respectively. After gelation, the content of ferulic acid dimers decreased from 0.135 to 0.03 µg/mg MBAX, suggesting the formation of ferulated structures unreleased by mild alkaline hydrolysis. MBAX microspheres presented an average diameter of 531 µm and a swelling ratio value (q) of 18 g water/g MBAX. The structural parameters of MBAX microspheres were calculated from equilibrium swelling experiments, presenting an average mesh size of 52 nm. Microstructure and textural properties of dried MBAX microspheres were studied by scanning electron microscopy and nitrogen adsorption/desorption isotherms, respectively, showing a heterogeneous mesoporous and macroporous structure throughout the network.

Synthesis, characterization, and drug release properties of poly(N‐isopropylacrylamide) gels prepared in methanol–water cononsolvent medium

AbstractPoly(N‐isopropylacrylamide) (PNIPAM) hydrogels were simply prepared by free radical polymerization in different methanol–water mixture. A scanning electron microscopy study revealed that the freeze‐dried hydrogels were macroporous. The swelling ratios in water at 20°C of the resulting hydrogels followed the order: X0.43>X0.21>X0.76 ≈ X0.57>X0.31>X0.13>X0.06>X0, where Xm denotes a gel prepared in a methanol–water mixture with m mole fraction of methanol (xm). Below the lower critical solution temperature, the swelling ratio values of all of the hydrogels gradually decreased with the increase in the temperature. The complete collapse of the PNIPAM chain of all the 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 the PNIPAM gels in the methanol–water mixtures with different xm values at 20°C passed through a minimum in the cononsolvency zone. The deswelling rates of the hydrogels decreased in the following order: X0.43> X0.31> X0.21> X0.57> X0.76 ≈ X0.13> X0.06> X0. The reswelling rates of these hydrogels decreased in the following order: X0> X0.31> X0.06 ≈ X0.13 > X0.76> X0.57> X0.21> X0.43. The release rates of the Tramadol Hydrochloride drug at 37°C from the drug‐loaded hydrogels were almost same for all of the hydrogels. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Mechanical, swelling, and thermal aging properties of marble sludge-natural rubber composites

A large amount of post-consumer marble sludge waste is thrown away into landfills. The need to reuse this waste is increasing day by day due to the environmental concern and energy conservation. The purpose of this work is to explore the use of this waste for low-cost natural rubber composites. In the experimental part, three different microsizes: 10, 20, and 75 μm, with five different levels of loading up to 90 parts per hundred of rubber (pphr) were used in natural rubber (NR) composites to study the effect of marble sludge (MS) loading on the mechanical properties. Application of MS as filler enhanced many properties such as tensile strength, modulus, tear strength, hardness, and rebound resilience. It is observed that compression set, abrasion loss, cross-link density, and shear modulus increased, while rebound resilience and swelling ratio values decreased with increasing MS loading. Mechanical properties of the NR composite filled with 10-μm MS are higher than those of NR composites containing 20- and 75-μm MS. The effect of thermal aging at 70°C and 100°C for 96 h has also been studied. This study has thus shown that MS from marble processing industrial waste can be used as economical alternative filler in NR compounding.

Synthesis and characterization of porous poly(N‐isopropylacrylamide) hydrogels prepared in ethanol–water mixtures

AbstractPoly(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: X0.34 ≈ X0.68 > X0.48 > X0.09 > X0.04 > X0, where Xa 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: X0.34 > X0.48 > X0.68 > X 0.09 > X0.04 > X0. The reswelling rates of these hydrogels decreased in the following order: X0 > X0.04 ≈ X0.48 > X0.09 ≈ X0.68 > X 0.34. The freeze‐drying process decreased the swelling ratios but increased the deswelling and reswelling properties of the PNIPAM gels. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

Synthesis of novel tetrahydrofuran-epichlorohydrin [poly(THF-b-ECH)] macromonomeric peroxy initiators by cationic copolymerization and the quantum chemically investigation of initiation system effects

Cationic polymerization of tetrahydrofuran (THF) and epichlorohydrin (ECH) was performed with peroxy initiators synthesized from bis (4,4′-bromomethyl benzoyl peroxide (BBP) or bromomethyl benzoyl t-butyl peroxy ester (t-BuBP) and AgSbF6 or ZnCl2 system at 0 °C to obtain the poly(THF-b-ECH) macromonomeric peroxy initiators. Kinetic studies were accomplished for poly(THF-b-ECH) initiators. Poly(THF-b-ECH-b-MMA) and poly(THF-b-ECH-b-S) block copolymers were synthesized by bulk polymerization of methyl methacrylate (MMA) and styrene (S) with poly(THF-b-ECH) initiators. The quantum chemical calculations for the block copolymers, the initiating systems of the cationic polymerization of THF and ECH were achieved using HYPERCHEM 7.5 program. The optimized geometries of the polymers were investigated with the quantum chemical calculations. Poly(THF-b-ECH) initiators having peroxygen groups were used for graft copolymerization of polybutadien (PBd) to obtain poly(THF-b-ECH-g-PBd) crosslinked graft copolymers. The graft copolymers were investigated by sol-gel analysis. Swelling ratio values of the graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by FTIR, 1H NMR, GPC, SEM, TEM, and DSC techniques. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2896–2909, 2010

ATRP of methyl methacrylate initiated with a bifunctional initiator bearing bromomethyl functional groups: Synthesis of the block and graft copolymers

This article reports the synthesis of the block and graft copolymers using peroxygen-containing poly(methyl methacrylate) (poly-MMA) as a macroinitiator that was prepared from the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) in the presence of bis(4,4'-bromomethyl benzoyl peroxide) (BBP). The effects of reaction temperatures on the ATRP system were studied in detail. Kinetic studies were carried out to investigate controlled ATRP for BBP/CuBr/bpy initiating system with MMA at 40 degrees C and free radical polymerization of styrene (S) at 80 degrees C. The plots of In ([M-o]/[M-t]) versus reaction time are linear, corresponding to first-order kinetics. Poly-MMA initiators were used in the bulk polymerization of S to obtain poly (MMA-b-S) block copolymers. Poly-MMA initiators containing undecomposed peroygen groups were used for the graft copolymerization of polybutadiene (PBd) and natural rubber (RSS-3) to obtain crosslinked poly (MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values (q(v)) of the graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by Fourier-transform infrared spectroscopy (FTIR), H-1-nuclear magnetic resonance (H-1 NMR), gel-permeation chromatography (GPC), differential scanning calorimetry (DSC), thermogravimetric analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), and the fractional precipitation (gamma) techniques.

Synthesis and Characterization of a Novel Macromonomer Initiator for Reversible Addition Fragmentation Chain Transfer (RAFT). Evaluation of the Polymerization Kinetics and Gelation Behaviors

Reversible addition fragmentation chain transfer, RAFT, self condensing a novel macromonomer initiator polymerization and copolymerization with methyl methacrylate, MMA, in the presence of 2,2′ -azobisisobutyronitrile, AIBN, has been reported. RAFT-MIM was obtained from potassium salt of the ethyl xanthegonate and the terminally brominated poly (ethylene glycol) methacrylate (v-PEG-Br) which was synthesized by the reaction of poly (ethylene glycol) methacrylate, v-PEG-OH with Mn = 526 Dalton and 3-bromopropionyl chloride. Self condensing RAFT-MIM polymerization and copolymerization with MMA gave highly branched and cross-linked amphiphilic copolymers. The kinetic parameters were evaluated by changing some polymerization conditions such as monomer, initiator and solvent concentration, polymerization time and polymerization temperature. The plots of ln (M0/M) versus reaction time are linear, corresponding to first-order kinetics. The overall polymerization rate constant, k, was calculated as 7.9 × 10−5 s−1. The products were characterized by 1H-NMR and TGA. Swelling ratio values of the crosslinked products in CHCl3 were also determined.

Effect of Co-Monomer Content on Rheological Property of Sawdust/ABS Composites

Effect of co-monomer content in Acrylonitrile-Butadiene-Styrene copolymer (ABS) on the rheological property of sawdust reinforced ABS composites was investigated using capillary die rheometer. Three grades of commercial ABS resin were used. Sawdust from Para rubber tree treated with N-2(aminoethyl) 3-aminopropyl trimethoxy silane was blended with ABS by melt blending process using twin-screw extruder. From the results, shear thinning behavior was found for all of composites in the same shear rate ranges for testing that were investigated. At the low shear rate, the composites which contain higher acrylonitrile content, showed higher viscosity. At high shear rate, the viscosity of each co-monomer dependent composites tends to come close to each other on the curves. In this study, Carreau’s model was used for curve fitting and those parameters were also determined. Die swell ratio of the composites tended to increase at the initial ranges of shear rate of 10-500 s-1, and then the swelling ratio value decreased dramatically once the shear rate were further applied. The molecular weight has more effects than comonomer content on the die swell behavior i.e., at the same molecular weight, composites with higher butadiene content show higher swelling ratio.

Synthesis of a New Macroperoxy Initiator with Methyl Methacrylate and T-Butyl Peroxy Ester by Atom Transfer Radical Polymerization and Copolymerization with Conventional Vinyl Monomers

In this study, we present the synthesis of poly-MMA macroperoxy initiators obtained by the ATRP of MMA with bromo methyl benzyl t-butyl peroxy ester (t-BuBP) as an initiator, and CuX (X:Br or Cl)/2,2′-bipyridine (bpy) as a catalyst system at 0, 20, 30 and 40°C. The peroxygen groups do not decompose during the ATRP reaction, because low reaction temperatures used for the ATRP reaction are not enough to decompose them. The peroxygen groups of poly-PMMA macroperoxy initiators can lead them to react with a monomer by using appropriate reaction conditions to obtain the block or graft copolymers. For this purpose, poly-MMA macroperoxy initiators were used to synthesize poly(MMA-b-S) block copolymers with S and used for graft copolymerization of polybutadiene (PBd) and natural rubber (RSS-3) to obtain crosslinked poly(MMA-g-PBd) and poly(MMA-g-RSS-3) graft copolymers. Swelling ratio values of the crosslinked graft copolymers in CHCl3 were calculated. The characterizations of the polymers were achieved by FT-IR, 1H-NMR, GPC, DSC, SEM, and the fractional precipitation (γ) techniques. The reaction schemes were also performed using the HYPERCHEM 7.5 program. The mechanical properties of the products were investigated.

Photocrosslinked electrospun chitosan‐based biocompatible nanofibers

AbstractThe electrospun fibers chitosan/polyvinyl alcohol (CS/PVA) were crosslinked by the incorporation of photocrosslinking agent poly(ethyleneglycol)‐600‐dimethacrylate (PEGDMA) and photoinitiator 2‐hydroxy‐1‐[4‐(2‐hydroxyethoxy)phenyl]‐2‐methyl‐1‐propanone (HEPK) into the spinning solutions and a subsequent irradiation by UV light. The photocrosslinking process of CS‐based nanofibers was studied by the Fourier transform infrared spectra, and the water resistance was investigated by scanning electron microscopy (SEM) and water swelling measurement. The results indicated that the water resistance of photocrosslinked CS‐based nanofibers was improved obviously and the swelling ratio decreased with the increasing content of PEGDMA/HEPK. When the concentration of crosslinking agent was 20 wt %, the swelling ratio value decreased to half of that in none crosslinking CS/PVA nanofiber membranes, further increasing the concentration of crosslinking agent to 50 wt %, the swelling ratio value was one eighth of the none crosslinking CS/PVA nanofiber membranes. Cytotoxicity evaluation by 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay indicated that the photocrosslinked CS‐based fiber membranes were nontoxic to L929 cells. Results from cell culture SEM imaging showed that cells which exhibited the spindle shape could grow properly on the surface of nanofibrous structure of the CS/PVA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Preparation and characteristics of crosslinked sulfonated poly(phthalazinone ether sulfone ketone) with poly(vinyl alcohol) for proton exchange membrane

In order to further overcome the trade-off between high conductivity and good mechanical property of proton exchange membrane (PEM), direct covalent crosslinking of sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) and poly(vinyl alcohol) (PVA) was prepared through post-heating process. Polymer PVA has attractive advantages to be a crosslinker with SPPESK, since the crosslinking of SPPESK with PVA requires relatively lower crosslinking temperature and has much higher stability in water, compared with small molecule crosslinker of glycol and glycerol. The crosslinking is confirmed by solubility change and analysis of ion exchange capacity (IEC) and sulfur content ( C S) of uncrosslinked and crosslinked SPPESK with PVA (Un S-P and Cr S-P). Calculation of degree of crosslinking (DC) of sulfonic group shows that most –SO 3Hs of SPPESK are not involved in the crosslinking, which can maintain the ion exchange and proton transport function. ATR-FTIR spectra analysis manifests the PVA in Cr S-P are oxidized and dehydrated during the crosslinking process with SPPESK. Cr S-P membrane still has higher thermal stability, despite T d (252–273 °C) is less than that (306 °C) of pristine SPPESK. SEM images and XRD patterns show that the Cr S-P is a homogenous and amorphous material. Water uptake of Cr S-P membrane decreases with increasing PVA content, and Cr S-P membrane with lower PVA content (e.g. 15% and 20%) has high water uptake (111.1% and 98.0%) at 80 °C. All the swelling ratio values of Cr S-P (15–35% of PVA content) are at a lower level (≤36%) even at 80 °C. Some Cr S-P membranes (with lower PVA content) have much higher conductivity than that of stable pristine SPPESK, e.g. conductivity of S-P 85/15 reaches 2.00 × 10 −2 S cm −1 which is almost twice as that (1.03 × 10 −2 S cm −1) of SPPESK DS 81% membrane. All above properties of Cr S-P membrane (especially PVA content: 15–20%) indicate the kind of crosslinked sulfonated polymer with PVA is another alternative or prospective approach to prepare PEM.

Effect of filler treatments on rheological behavior of calcium carbonate and talc‐filled polypropylene hybrid composites

AbstractCommercial stearic acid treated calcium carbonate (CaCO3) was used to make a comparative study on rheological behavior of the CaCO3 and talc‐filled polypropylene (PP) hybrid composites with nontreated filler. Apparent shear viscosity and extrudate swell were investigated with variation of filler ratio and temperature with 30% by weight total of filler was used in PP composite. The Shimadzu capillary rheometer was used to evaluate shear viscosity and shear rate of the composite. It was found that the shear viscosities decrease with increasing shear rate. The apparent shear viscosity of the composite containing the stearic acid treated is slightly lower than untreated filler. Shear thickening behavior at higher shear rate has also shown by 15/15 treated composites at higher temperature about 220°C and investigation by SEM has proved that filler being densely packed at that condition. Treated composites also exhibit lower swelling ratio value than untreated composite, and swelling ratio also decreases linearly with increasing temperature and the die length–diameter ratio. It is believed that dispersion of filler play an important role not only on shear viscosity but also on swelling ratio of PP composite. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5421–5426, 2006

Synthesis of novel macromonomeric peroxy initiators of styrene with the cationic copolymerization and the quantum chemically investigation of the initiation system effects

AbstractCationic polymerization of styrene (S) was performed with peroxy initiators synthesized from bis(4,4′‐bromomethyl benzoyl peroxide) (BBP) or bromomethyl benzoyl t‐butyl peroxy ester (t‐BuBP) and AgSbF6 or ZnCl2 system at 0 and −10°C to obtain macromonomeric peroxy initiators (poly‐S initiators). Kinetic studies were accomplished for poly‐S initiators. Poly(styrene‐block‐methyl methacrylate) block copolymers [poly(S‐b‐MMA)] were synthesized by bulk polymerization of methyl methacrylate (MMA) with poly‐S initiators. The quantum chemical calculations for the initiating systems of the cationic polymerization of S and poly(S‐b‐MMA) block copolymers were achieved using Hyperchem 7.5 program. The optimized geometries of the polymers were investigated with the quantum chemical calculations. Poly(S‐b‐MMA) block copolymers containing undecomposed peroxide groups were used to initiate thermal copolymerization of acrylic acid (AA) to obtain crosslinked poly(S‐b‐MMA‐b‐AA) multicomponent copolymers. The crosslinked multicomponent copolymers were investigated by sol–gel analysis. Swelling ratio values of the crosslinked multicomponent copolymers in CHCl3 were calculated. Poly‐S initiators having undecomposed peroxygen groups were used for graft copolymerization of polybutadien (PBd) to obtain crosslinked poly(S‐graft‐polybutadien) graft copolymers [poly(S‐g‐PBd)]. The characterizations of the polymers were achieved by FTIR, 1H‐NMR, GPC, SEM, and DSC techniques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 348–357, 2006

Synthesis of Copoly(aryl ether ether nitrile)s Containing Sulfonic Acid Groups for PEM Application

Wholly aromatic poly(aryl ether ether nitrile)s containing sulfonic acid groups (SPAEEN)s, intended for fuel cells applications as proton conducting membrane materials, were first prepared via nucleophilic substitution polycondensation reactions. SPAEEN copolymers were synthesized by potassium carbonate-mediated nucleophilic polycondensation reactions of commercially available monomers: 2,6-difluorobenzonitrile (2,6-DFBN), potassium 2,5-dihydroxybenzenesulfonate (sulfonated hydroquinone SHQ), and a third monomer 4,4‘-biphenol or hydroquinone in N-methyl-2-pyrrolidone (NMP) at 160 °C. The sulfonic acid group content (SC), expressed as a number per repeat unit of polymer, ranged from 0.5 to 1.0 and was obtained by changing the feed ratio of SHQ to the unsulfonated bisphenol. Membrane films in potassium salt and acid forms were obtained by casting N,N-dimethylacetamide (DMAc) solution of SPAEEN copolymers, followed by immersing in 2 N sulfuric acid at room temperature. FT-IR confirmed the structure of polymer in both salt and acid forms. NMR was used to determine the obtained SC values of the SPAEEN series. Glass transition temperatures (Tgs) of SPAEEN copolymers (potassium form) determined by differential scanning calorimetry (DSC) ranged from 308 to 371 °C. Decomposition temperatures (Tds) of SPAEEN were around 300 °C for acid form and over 400 °C for potassium form. Water uptake and swelling ratio values increased with SC and temperature. All SPAEENH copolymers were mechanically stronger than Nafion117 and exhibited a reasonable flexibility. The proton conductivities of acid form membrane at different SC values were close to or higher than that of Nafion117 and reached 10-1 S/cm. The best compromise on PEM mechanical strength, water swelling, and proton conductivity was achieved at SC ranging from 0.5 to 0.7.

Synthesis of Poly(arylene ether ether ketone ketone) Copolymers Containing Pendant Sulfonic Acid Groups Bonded to Naphthalene as Proton Exchange Membrane Materials

A new series of wholly aromatic poly(ether ether ketone ketone) containing pendant sulfonic acid groups (SPAEEKK) were conveniently prepared by potassium carbonate mediated nucleophilic polycondensation reactions of inexpensive commercially available monomers 1,3-bis(4-fluorobenzoyl)benzene (BFBB), sodium 6,7-dihydroxy-2-naphthalenesulfonate (DHNS), and 4,4‘-biphenol or hydroquinone in N-methyl-2-pyrrolidone (NMP) at 170 °C. FT-IR and NMR were used to characterize the structures and the sulfonate or sulfonic acid contents (SC) of the polymers. Flexible membrane films were obtained by casting N,N-dimethylacetamide (DMAc) solutions of copolymers. Membrane films in acid form were then obtained by treating the sodium form membrane films in 2 N sulfuric acid at room temperature. Glass-transition temperatures (Tg's) and decomposition temperatures (Td's) of SPAEEKKs in both sodium and acid forms were determined. Water uptake and swelling ratio values increased with SCs and temperatures. The proton conductivities...

Preparation and characterization of physical gels and beads from chitin solutions

A detailed account of physical bulk gel and bead formation from various chitin solutions and nonsolvents is given. Instant gel formation occurs upon contact of chitin solutions in dimethylacetamide (DMAc)/lithium chloride (LiCl) or N-methyl-pyrrolidinone (NMP)/LiCl solvents and nonsolvents such as water, ethanol, or acetone. Ethanol was found to be the optimal nonsolvent for homogeneous spherical bead formation from chitin solutions. Similarly, DMAc-based chitin solutions proved to yield higher quality beads compared to NMP-based solutions. The differences in bead morphology, crystallinity, and thermal degradation are explained in light of the attainment of a balance between attractive hydrogen bonding in the chitin gel network and segment–nonsolvent interactions. The dependence of swelling of chitin gels on pH indicated a maximum of swelling ratio value of 4.3 at pH 11 in aqueous solutions while the equilibrium swelling ratio value of chitin beads formed with ethanol reached a maximum of 2.4. Bulk gels formed under favorable conditions were demonstrated to be recyclable after solvent separation and drying.