Drug diffusion in hydrophobically modified N,N-dimethylacrylamide hydrogels

The use of hydrophobically modified hydrogels for drug release was investigated. Copolymers of N,N-dimethylacrylamide and 2-(N-ethyl-perfluorooctanesulfonamido) ethyl acrylate (FOSA) were prepared by free-radical polymerization. The drug release rates, dynamic swelling behavior, and pH sensitivities of copolymers ranging in composition from 0 to 30 mol% FOSA were studied. Pheniramine maleate, an ocular antihistamine, was used as the model drug substance. Hydrogels of DMA produced with increasing amounts of FOSA had a decreased equilibrium media content and exhibited a slower drug release rate. Early-time, late-time and Etters approximation drug diffusion coefficients ranged from 0.4×10⁻³ to 12.3×10⁻³ mm²/min. The diffusion of the drug model was less sensitive to pH of the buffered media over the range of pH 4-8, but increasing the media pH slowed the permeability slightly by decreasing the swellability of the hydrogel. The power law exponent (n≈0.5) and the swelling interface number (Sw?1) suggested that the drug release mechanism from these hydrogels was Fickian and not swelling controlled. These novel thermoprocessible hydrogels have potential to be used as controlled ocular drug delivery devices (e.g. contact lenses or ocular inserts).     

Partially biobased polyamphiphile-bearing reactive epoxy groups in the side chains and its application to the hydrogel

Partially biobased polyamphiphile-bearing reactive epoxy groups in the side chains were obtained in 62–78 % yields by a radical copolymerization of limonene oxide (LO) and PEG methylacrylate (PEGA) with different feed ratios. Degree of LO incorporation into the copolymer was determined as 12–23 % by ¹H NMR spectroscopic analysis. The copolymer having LO unit:PEGA unit = 19:81 formed polymer associates in water, particle diameter of which was ranged mainly from 4 to 66 nm and hydrodynamic mean diameter was 12.3 nm. Its critical micelle concentration was determined as 0.53 g/L by fluorescence spectroscopic analysis. A cross-linking reaction of the epoxy groups in the side chains was conducted with 3.97 mol% (to the epoxy group) of branched poly(ethylene imine) as a cross-linker to give the corresponding hydrogel in 56 % yield. The hydrogel can absorb water as much as 13 times its own mass.     

Photo‐crosslinked poly(ethylene glycol) diacrylate (PEGDA) hydrogels from low molecular weight prepolymer: Swelling and permeation studies

The aim of this work was to assess the diffusive properties of poly(ethylene glycol) diacrylate (PEGDA)‐based hydrogels, derived from low MW prepolymers, in view of potential biomedical applications. Several hydrogels were synthesized through UV irradiation of PEGDA solutions for different exposure times. Swelling measurements in distilled water were performed to estimate the yielded crosslink density, while swelling tests at 37 °C in selected media allowed to analyze the mesh size changes induced by various pH and ionic strength (IonS) conditions. The transport of glucose and insulin through thin hydrogel membranes was finally assessed in a modified Ussing chamber at physiological values of pH and IonS (7.4 and 150 mM, respectively). Results showed that the swelling was dependent on the IonS (with swelling reductions up to 20–30% for IonS increases in the range 0–300 mM) and, to a lesser extent, on the pH of the surrounding medium (with swelling increments of about 10% for increasing pH in the range 2.5–11). All hydrogels were also permeable to glucose and insulin, which displayed comparable diffusion coefficients (in the order of 10^?6 cm²/s). Specific interactions between glucose and the polymer chains were evidenced by values of the partition coefficient higher than unity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44380.     

Crosslinking poly(1-trimethylsilyl-1-propyne) and its effect on solvent resistance and transport properties

Poly(1-trimethylsilyl-1-propyne) (PTMSP) has been crosslinked using 3,3′-diazidodiphenylsulfone to improve its solvent resistance. This study reports the influence of crosslinker content on the solubility properties of PTMSP, its density, and its gas sorption and transport properties. Crosslinking PTMSP renders it insoluble even in excellent solvents for the uncrosslinked polymer. Gas permeability and fractional free volume (FFV) decreased as crosslinker content increased, while gas sorption was unaffected by crosslinking. Therefore, the reduction in permeability upon crosslinking PTMSP was due to decreases in diffusion coefficients. Permeability reductions due to crosslinking could be offset by adding nanoparticles to the films. The addition of 30 wt.% fumed silica nanoparticles increased the permeability of crosslinked PTMSP by approximately 80%. In mixed gas permeation experiments, when the composition of the feed gas was 98 mol% CH₄ and 2 mol% n-C₄H₁₀, uncrosslinked PTMSP had an n-C₄H₁₀/CH₄ selectivity of 31 and an n-C₄H₁₀ permeability of 114,000 barrers at 35 °C and 14 atm feed fugacity. At the same conditions, crosslinked PTMSP containing 5 wt.% crosslinker had an n-C₄H₁₀/CH₄ selectivity of 28 and an n-C₄H₁₀ permeability of 73,000 barrers, and crosslinked PTMSP containing 5 wt.% crosslinker and 30 wt.% fumed silica nanoparticles had an n-C₄H₁₀/CH₄ selectivity of 21 and an n-C₄H₁₀ permeability of 110,000 barrers.     

Poly(vinyl alcohol)-based polymer electrolyte membranes for direct methanol fuel cells

We have prepared polymer electrolyte membranes (PEMs) from poly(vinyl alcohol) (PVA) and modified PVA polyanion containing 2 or 4 mol% of 2-methyl-1-propanesulfonic acid (AMPS) groups as a copolymer. The PEMs of various AMPS content and cross-linking conditions were prepared to determine the effect of AMPS content and cross-linking conditions on PEM properties. Proton conductivity and permeability of methanol through the PEMs increased with increasing AMPS content, C_AMPS, and with decreasing cross-linker concentration, C_GA, because of the increase in the water content. The permeability coefficient of methanol through the PEM prepared under the conditions of C_AMPS = 2.7 mol% and C_GA = 0.35 vol% was about 30 times lower than that of Nafion^®117 under the same measurement conditions. The proton permselectivity of the PEM, which is defined as the ratio of the proton conductivity to the permeability coefficient of methanol, gave a maximum value of 66 × 10³ S cm⁻³ s. The value is about three times higher than that of Nafion^®117.     

Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

Impedance evaluation of permeability and corrosion of Al-2024 aluminum alloy coated with a chromate free primer

The corrosion of AA-2024 aluminum alloy protected with a chromate free primer is investigated after immersion in a 0.5 M NaCl aqueous solution. The water uptake by the coating increases continuously when the film, applied on an aluminum AA-2024 substrate, is placed in the 0.5 M NaCl solution. This increase is attributed to corrosion reactions taking place at the alloy/coating interface when water molecules reach the interface. The maximum water volume fraction absorbed by a similar coating applied on platinum substrate is 3.5 vol% and the permeability is 7.6 × 10⁻¹² m² s⁻¹. After 72 h immersion in the 0.5 M NaCl solution, the Nyquist representation of impedance data shows transmission line behavior that can be assigned to percolation pathway along the filler particles after water uptake. Charge transfer and diffusion of corrosion reactants and products occur, but no delamination was observed for immersion longer than 172 h. Furthermore, the coating resistance is still close to 10⁸ Ω cm⁻² after this immersion time. This accounts for the good protective performance of the coating.     

Superporous poly(2-hydroxyethyl methacrylate) based scaffolds: Preparation and characterization

Superporous poly(2-hydroxyethyl methacrylate) (PHEMA) scaffolds with pore size from 10¹ to 10² μm range were prepared by radical polymerization of 2-hydroxyethyl methacrylate (HEMA) with 2 wt.% ethylene dimethacrylate (EDMA) with the aim to obtain a support for cell cultivation. Superpores were formed by salt-leaching technique using NaCl or (NH₄)₂SO₄ as a porogen. Addition of liquid porogen (cyclohexanol/dodecan-1-ol (CyOH/DOH) = 9/1 w/w) to the polymerization mixture did not substantially affect the formation of meso- and macropores. The prepared slabs were characterized by several methods including water and cyclohexane regain by centrifugation, water regain by suction, scanning electron microscopy (SEM), mercury porosimetry and dynamic desorption of nitrogen. High-vacuum scanning electron microscopy (HVSEM) confirmed permeability of hydrogel slabs to 8-μm microspheres, whereas low-vacuum scanning electron microscopy (LVSEM) at cryo-conditions showed the undeformed structure of the frozen slabs. Interconnection of pores in the PHEMA slabs was proved. Water regain estimated by centrifugation method did not include volume of large superpores (imprints of porogen crystals), in contrast to water regain by suction method. The porosities of the slabs ranging from 81 to 91% were proportional to the volume of porogen in the feed.     

Sulfur-containing hyperbranched polymeric photoinitiator end-capped with benzophenone and tertiary amine moieties prepared via simultaneous double thiol-ene click reactions used for UV curing coatings

A series of sulfur-containing hyperbranched polymeric photoinitiators end-capped with benzophenone (BP) and tertiary amine moieties (B/A-HPIs) were synthesized via the simultaneous double thiol-ene click reactions of thiolated hyperbranched polymer with both dimethylaminoethyl acrylate and 3-(4-benzoylphenoxy)propyl acrylate. The molecular structures were characterized by ¹H NMR and FT-IR spectroscopy. From the UV-vis spectra, B/A-HPIs showed the stronger n-π* absorption at ∼340 nm with a higher molar extinction coefficients of 371 L mol⁻¹ cm⁻¹ than 148 L mol⁻¹ cm⁻¹ of BP, and an obvious red shift of π-π* absorption from ∼250 nm of BP to ∼280 nm. According to the photo-DSC study, the photopolymerization rate of 1,6-hexanediol diacrylate initiated by 5 wt% B/A-HPI was twice higher than that by BP. The DMTA results showed the good miscibility of B/A-HPIs with acrylate resins and high crosslinking density of cured films.     

Preparation of poly(acrylonitrile-butyl acrylate) gel electrolyte for lithium-ion batteries

Poly(acrylonitrile-butyl acrylate) gel polymer electrolyte was prepared for lithium ion batteries. The preparation started with synthesis of poly(acrylonitrile-butyl acrylate) by radical emulsion polymerization, followed by phase inversion to produce microporous membrane. Then, the microporous gel polymer electrolytes (MGPEs) was prepared with the microporous membrane and LiPF₆ in ethylene carbonate/diethyl carbonate. The dry microporous membrane showed a fracture strength as high as 18.98 MPa. As-prepared gel polymer electrolytes presented ionic conductivity in excess of 3.0 × 10⁻³ S cm⁻¹ at ambient temperature and a decomposition voltage over 6.6 V. The results showed that the as-prepared gel polymer electrolytes were promising materials for Li-ion batteries.     

Synthesis and characterization of sulfonated bromo-poly(2,6-dimethyl-1,4-phenylene oxide)-co-(2,6-diphenyl-1,4-phenylene oxide) copolymer as proton exchange membrane

Novel polymer electrolyte membranes containing the sulfonic acid groups attached on polymer backbone and side group simultaneously were synthesized. The bromo-poly(2,6-dimethyl-1,4-phenylene oxide)-co-(2,6-diphenyl-1,4-phenylene oxide) copolymer (BrcoPPO) was prepared by oxidative coupling polymerization with 2,6-dimethyl phenol, 2,6-diphenyl phenol, CuCl(I) and pyridine, and followed by bromination with bromine. Copolymer was maintained in 2,6-diphenyl phenol 10 mol% and 2,6-dimethyl phenol 90 mol%. Sulfonation of BrcoPPO (S-BrcoPPO) was carried out in a chlorobenzene solvent using chlorosulfonic acid. The polymeric membranes were cast from dimethylsulfoxide solution. The membranes were studied by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). Sorption experiments were conducted to observe the interaction of sulfonated polymers with water and methanol. S-BrcoPPO membranes exhibited proton conductivities from 2.3 × 10⁻³ to 1.4 × 10⁻² S/cm, water uptake from 7.00 to 49.43%, IEC from 0.58 to 1.38 mequiv./g, methanol permeability from 1.9 × 10⁻⁷ to 3.5 × 10⁻⁷ cm²/S.     

Water sorption and diffusion in starch/polyolefin blends

The kinetics of water sorption by starch filled polyolefins has been investigated using blends of commercial starch masterbatch with low density polyethylene (LDPE), high density PE (HDPE), and copolymers of ethylene with methyl acrylate (EMA), ethyl (EEA), AND n-butyl acrylate (EBA). Transient state diffusion coefficients (D) of water in the blends were determined using Fickian analysis of the initial stages of the sorption isotherms. Measured D values were several orders of magnitude lower than values reported for either pure starch of LIDPE by various investigators. Resin effects on D were on the order D_HDPE < D_LDPE ? D_EBA < D_EEA < D_EMA. The resin effects diminished as the starch content increased. The lower magnitude of D in the blends relative to pure LDPE was attributed to the sorption of water by the dry starch particles, in a manner similar to dual-mode sorption in glassy polymers. Copolymer effects were consistent with reduction in crystallinity caused by the comonomers. The dependence of the diffusion coefficient on starch content was not described by mixing models of heterogeneous systems of percolation theory.     

Photopolymer kinetics using light intensity gradients in high-throughput conversion analysis

Light intensity gradients and light exposure time gradients were combined to produce contours of constant dose on a sample substrate. These polymerized samples were subsequently analyzed using high-throughput Fourier transform infrared spectroscopy to measure conversion as a function of both gradients. Three (meth)acrylate monomers were analyzed over light doses ranging from 0 mJ/cm² to 920 mJ/cm², demonstrating that in thin films, higher light intensities at a constant light dose produce higher conversion due to a decreased oxygen inhibition time and larger thermal excursions. At a light dose of 75 mJ/cm², the conversion of 2-ethylhexyl acrylate increases from 40 ± 2% at a light intensity of 0.9 mW/cm² to 59 ± 3% at 7.2 mW/cm². The two acrylate monomers exhibited rapid photopolymerization up to a specific conversion, after which additional radiation dose produced only marginal increases in overall conversion. For hexanediol diacrylate, a light dose of 300 mJ/cm² was the minimum amount required to reach the maximum conversion over the entire range analyzed. For the dimethacrylate system, a similar effect was seen, with a reduced oxygen inhibition time and conversion above 70% showing a similar conversion at a constant light dose of 500 mJ/cm². In all three systems, dose contours were used to determine a range of light intensities at which a statistically similar conversion would occur for a specified light dose.     

The partition coefficients of ethylene between hydrate and vapor for methane + ethylene + water and methane + ethylene + SDS + water systems

The hydrate formation of CH₄+C₂H₄ mixture was studied experimentally in two different cases, with and without the presence of sodium dodecyl sulfate (SDS) in water. The results manifested that the presence of SDS could not only accelerate the hydrate formation process, but also increase the partition coefficient of ethylene between hydrate and vapor drastically. The partition coefficients of ethylene between hydrate and vapor for methane + ethylene + water with the presence of 500 ppm SDS in water were then systematically measured. The experimental temperature ranged from 273.15 to 278.15 K, the pressure ranged from 2.5 to 5.5 MPa, the initial gas-liquid volume ratio ranged from 95 to 240 standard volumes of gas per volume of liquid, and the mole percentage of ethylene in feed gas mixture ranged from 5.28% to 79.36%. The results demonstrated that ethylene could be enriched in hydrate phase and partition coefficients were increased with the presence of SDS in water. This conclusion is of industrial significance; it implies that it is feasible to recover ethylene from gas mixture, e.g., various kinds of refinery gases or cracking gases in ethylene plant, by forming hydrate.     

Modification of Nafion membranes with ternary composite materials for direct methanol fuel cells

Composite membranes for direct methanol fuel cells (DMFCs) were prepared by using Nafion115 membrane modification with polyvinyl alcohol (PVA), polyimide (PI) and 8-trimethoxysilylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS). The performance of the composite membranes was evaluated in terms of water sorption, dimensional stability, thermal stability, proton conductivity, methanol permeability and cell performance. The proton conductivity was slightly decreased by 1-3% compared with Nafion115, which still kept the high proton conduction of Nafion115. The methanol permeability of Nafion/PI-PVA-TSPS composite membranes was remarkably reduced by 35-55% compared with Nafion115. The power density of DMFCs with Nafion/PI-PVA-TSPS composite membranes reached to 100 mW/cm², exceeding that with Nafion115 (68m W/cm²).     

Characterization and determination of swelling and diffusion characteristics of poly(n‐vinyl‐2‐pyrrolidone) hydrogels in water

Hydrogels in the form of rods with varying crosslink densities and three‐dimensional network structures were prepared from Poly(N‐vinyl‐2‐pyrrolidone) (PVP)/water and PVP/water/persulfate systems by irradiation with γ rays at ambient temperature. Average molecular weights between crosslinks, percent swelling, swelling equilibrium values, diffusion/swelling characteristics (i.e., the structure of network constant, the type of diffusion, the initial swelling rate, swelling rate constant), and equilibrium water content were evaluated for both hydrogel systems. Water diffusion to the hydrogel is a non‐Fickian type diffusion and diffusion coefficients vary from 6.56 × 10⁻⁷ to 2.51 × 10⁻⁷cm²min⁻¹ for PVP and 6.09 × 10⁻⁷ to 2.14 × 10⁻⁷ cm²min⁻¹ for PVP/persulfate hydrogel systems. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 994–1000, 2000     

Effect of chemical structure and crosslinking density on the thermo-mechanical properties and toughness of (meth)acrylate shape memory polymer networks

The objective of this work is to characterize and understand structure-mechanical property relationships in (meth)acrylate networks. The networks are synthesized from mono-functional (meth)acrylates with systematically varying sidegroup structure and multi-functional crosslinkers with varying mole fraction and functionality. Fundamental trends are established between the network chemical structure, crosslink density, glass transition temperature, rubbery modulus, failure strain, and toughness. The glass transition temperature of the networks ranged from −29 to 112 °C, and the rubbery modulus (E_r) ranged from 2.8 to 129.5 MPa. At low crosslink density (E_r < 10 MPa) network chemistry has a profound effect on network toughness. At high crosslink densities (E_r > 10 MPa), network chemistry has little influence on material toughness. The characteristic ratio of the mono-functional (meth)acrylates' components is unable to predict trends in network toughness as a function of chemical structure, as has been demonstrated in thermoplastics. The cohesive energy density is a better tool for relative prediction of network mechanical properties. Due to superior mechanical properties, networks with phenyl sidegroups are further investigated to understand the effect of phenyl sidegroup structure on toughness.     

Preparation and properties of poly(ethylene oxide) gel filled polypropylene separators and their corresponding gel polymer electrolytes for Li-ion batteries

Poly(ethylene oxide) (PEO) filled polypropylene separators (GFPSs) are designed by means of thermal cross-linking of entrapped poly(ethylene glycol) methyl ether acrylate (PEGMEA) and poly(ethylene glycol) diacrylate (PEGDA) as gel constituents. The intrinsic properties of GFPS and their corresponding gel polymer electrolytes (GPE) are characterized by DSC, SEM, contact angle and electrochemical methods. It is found the stability of liquid electrolyte uptake in GPE could be improved obviously. For the GPE prepared from GFPS with filled polyether content of 14.3 wt%, the ionic conductivity could reach 1.12 × 10⁻³ S cm⁻¹ while the electrochemically stable window reach 5.0 V (vs. Li/Li⁺). These primary results show great promise of this simple method to prepare GPE for practical application in lithium ion batteries.     

Sulfonation and characterization of poly(styrene-isobutylene-styrene) triblock copolymers at high ion-exchange capacities

In this study, a triblock copolymer, poly(styrene-isobutylene-styrene), was sulfonated to eight different levels ranging from 0.36 to 2.04 mequiv./g (13 to 82 mol% of styrene; styrene is 19 mol% of the unsulfonated block copolymer). These sulfonated polymers were characterized with elemental analysis and infrared spectroscopy to confirm sulfonation and determine accurate sulfonation levels. Infrared analysis revealed four additional stretching vibrations as a result of sulfonation. Also, a linear relationship between absorbance at 1006 cm⁻¹ (stretching of the aromatic ring in styrene caused by the para-substituted sulfonic acid) and sulfonation level (measured by elemental analysis) was found. The density and water solubility of all the sulfonated polymers were measured and increased with increasing sulfonation level, as high as 1.31 g/cm³ and 351 wt%, respectively. In addition, a sulfonated triblock copolymer at 79 mol% sulfonation was neutralized with a cesium cation and revealed an increase in density, but a reduction in water solubility. This study demonstrates the resulting unique properties of sulfonated styrene-based block copolymers at higher ion-exchange capacities than previously reported.     

Anhydrous proton conducting polymer electrolytes based on poly(vinylphosphonic acid)-heterocycle composite material

The development of anhydrous proton conducting membrane is important for the operation of polymer electrolyte membrane fuel cell (PEMFC) at intermediate temperature (100-200 °C). In this study, we have investigated the acid-base hybrid materials by mixing of strong phosphonic acid polymer of poly(vinylphosphonic acid) (PVPA) with the high proton-exchange capacity and organic base of heterocycle, such as imidazole (Im), pyrazole (Py), or 1-methylimidazole (MeIm). As a result, PVPA-heterocycle composite material showed the high proton conductivity of approximately 10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. In particular, PVPA-89 mol% Im composite material showed the highest proton conductivity of 7×10⁻³ S cm⁻¹ at 150 °C under anhydrous condition. Additionally, the fuel cell test of PVPA-89 mol% Im composite material using a dry H₂/O₂ showed the power density of approximately 10 mW cm⁻² at 80 °C under anhydrous conditions. These acid-base anhydrous proton conducting materials without the existence of water molecules might be possibly used for a polymer electrolyte membrane at intermediate temperature operations under anhydrous or extremely low humidity conditions.