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•The conformational characteristics of PDET afford elastomeric PDET based PUs.•Polyurethanes with elongation values over 1000% were obtained.•Elastomeric PDET based polyurethanes can ...be categorized as gas barrier polymers.
The synthesis of linear and crosslinked polyurethanes based on α,ω-dihydroxypolydiethylene glycol terephthalate (PDET) is described. Prior to the preparation of these materials, a PDET polymer was obtained by conventional condensation reaction between dimethyl terephthalate and diethylene glycol, and a well-characterized fraction of PDET with number average molecular weight of 3,650 g mol−1 was chosen for the synthesis of the polyurethanes. Specifically, three polyurethanes were prepared: a pure linear polyurethane by reaction of PDET with 4,4′-diphenylmethane diisocyanate (MDI), a chain extended polyurethane obtained with MDI, PDET and 1,4-butanediol as chain extender, and a crosslinked polyurethane synthesized from PDET and a polyfunctional isocyanate. Thermal, mechanical, dielectric and gas transport properties of the polyurethanes were studied, showing excellent performance. In particular, rubber-like flexible materials were obtained with elongation values over 1000%, due to the low glass transition temperature of PDET. Furthermore, it was observed that these materials, in particular the crosslinked polyurethane, behave as gas barriers.
The enthalpies of combustion and sublimation of 1,3-dithiacyclohexane 1-oxide (1,3-dithiane sulfoxide, 2) were measured by a rotating-bomb combustion calorimeter and the Knudsen effusion technique, ...and the gas-phase enthalpy of formation was determined, Δf H°m(g) = −98.0 ± 1.9 kJ mol-1. This value is not as large (negative) as could have been expected from comparison with thermochemical data available for the thiane/thiane oxide reference system. High-level ab initio molecular orbital calculations at the MP2(FULL)/6-31G(3df,2p) level were performed, and the optimized molecular and electronic structures of 2 afforded valuable information on (1) the relative conformational energies of 2-axial and 2-equatorialthe latter being 7.1 kJ mol-1 more stable than 2-axial, (2) the possible involvement of n S → σ*C-S(O) hyperconjugation in 2-equatorial, (3) the lack of computational evidence for σS-C → σ*S-O stereoelectronic interaction in 2-equatorial, and (4) the relevance of a repulsive electrostatic interaction between sulfur atoms in 1,3-dithiane sulfoxide, which apparently counterbalances any n S → σ*C-S(O) stabilizing hyperconjugative interaction and accounts for the lower than expected enthalpy of formation for sulfoxide 2.
The conductive and diffusional behavior of electrolytes in media with different dielectric and viscoelastic properties is investigated. A revised model to separate the contribution of dissociated and ...nondissociated species to the diffusion coefficients determined with NMR is proposed. Impedance spectroscopy is used to measure the ionic conductivity of lithium salts in aqueous medium, ionic liquids in aprotic solvents, and hydrogel polyelectrolytes. The diffusion coefficients of the species of interest in those systems are determined with multinuclear pulsed-gradient spin–echo (PGSE) NMR. The results are analyzed using the revised model. It is shown that the degree of ionization could be determined directly from measurements of ionic conductivity and diffusion coefficients in very different types of electrolytes and in a wide range of concentrations. Furthermore, these findings support the original Arrhenius hypothesis about electrolytes and show that the assumption of a complete dissociation is not required to describe their conductive behavior. The reduced conductivity observed in hydrogels, at or near swelling equilibrium, compared to that in solutions could be attributed mainly to the hindered ionic mobility caused by the network structure.
•A variety of chitosan sulfate with different degree of sulfation was prepared.•Chitosan sulfate exhibited strong interaction with protein growth factors.•The effect of chitosan sulfate on neural ...stem cell depends on its chemical structure.
Despite the relevant biological functions of heparan sulfate (HS) glycosaminoglycans, their limited availability and the chemical heterogeneity from natural sources hamper their use for biomedical applications. Chitosan sulfates (ChS) exhibit structural similarity to HSs and may mimic their biological functions. We prepared a variety of ChS with different degree of sulfation to evaluate their ability to mimic HS in protein binding and to promote neural cell division and differentiation. The structure of the products was characterized using various spectroscopic and analytical methods. The study of their interaction with different growth factors showed that ChS bound to the proteins similarly or even better than heparin. In cell cultures, a transition effect on cell number was observed as a function of ChS concentration. Differences in promoting the expression of the differentiation markers were also found depending on the degree of sulfation and modification in the chitosan.
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•Chondroitin sulfate (CS) derivatives sulfation-dependently bind growth factors.•The disposition of the sulfates modulates the surface charge of the helical structure.•O-6 sulfation ...favours the arrangement of sulfates on the surface.•High-sulfated CS variants on the surface enhance the binding capacity.
Chondroitin sulfate (CS) is a relevant family of polysaccharides that participates in a large variety of biological events that are related to neural processes by regulating various growth factors through the pattern and degree of sulfation of the polysaccharide. However, their own complexity makes their optimization for biomedical applications a difficult undertaking. Thus, a different perspective has to be taken. Herein, we show that the particular sulfate distribution within the disaccharide repeating-unit plays a key role in the binding of growth factors (GFs). In particular, this disposition modulates the surface charge of the helical structure that, interestingly, has a significant influence on the binding capacity of CSs with several GFs. This fact should be carefully considered in the design of new ligands with improved activity as GFs ligands.
In liquids and in polymeric membranes, a precise determination of their transport properties is of paramount importance. In this work, an NMR method to measure sequentially the solubility and ...diffusion coefficients of carbon dioxide in liquids (n-alkanes and 1-alkanols) and in polymer membranes (polyethylene, polybutadiene, and polycarbonate) is described. The results show that NMR measurements are very reproducible and in good agreement with those determined by other methods. Considering that the gas permeability is defined as the product of the solubility and diffusion coefficients, the method allows the determination of all transport parameters in an accurate manner. The influence of chain length, viscosity, and solubility parameters on the transport coefficients of 13CO2 in alkanes and 1-alkanols was also analyzed and compared to those measured in polyethylene.
Ion gel polyelectrolytes (IGPs) were prepared by photopolymerization of the synthetic cationic monomers: 1-(2-methacryloyloxy)ethyl-3-butylimidazolium bis(trifluoromethane sulfonyl)imide ...(IMMATFSI)/bisfluorosulfonylimide (IMMAFSI) or 1-(2-methacryloyloxy)ethyl-1-methylpyrrolidinium bisfluorosulfonylimide (PYRMAFSI)/bis(trifluoromethane sulfonyl)imide (PYRMATFSI) in the presence of bis(trifluoromethane)sulfonamide (LiTFSI) solutions at different concentrations in either 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), 1-ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide (EMITFSI) or N -propyl- N -methylpyrrolidinium bis(fluorosulfonyl)imide (PMPFSI). The resulting IGPs are thermally stable, easy–to-handle solids wherein the overall ionic conductivity ranges from about 1 to about 10 mS cm −1 at 25 °C. The diffusivity of the ions Li, FSI and TFSI was studied at 25 °C by PGSE-NMR. In IGPs containing imidazolium groups both in the polycationic scaffold and the ionic liquid phase, their large Li ion diffusivities (up to 40 × 10 −12 m 2 s −1 , well above that of the anions) suggest the existence of an important contribution of anion exchange Li transport. To a lesser extent anion exchange may also be occurring in IGPs containing pyrrolidinium groups in the polycationic scaffold and imidazolium groups in the ionic liquid phase and to an even lesser extent in those IGPs with pyrrolidinium in both the polyelectrolyte and the ionic liquid phase. Because of the dimensional and thermal stabilities of IGPs, safety of their components, and their large Li-ion diffusivity, these types of electrolytes appear as excellent candidates for Li and Li-ion batteries.
Ion gel polyelectrolytes (IGPs) were prepared by photopolymerization of the synthetic cationic monomers: 1-(2-methacryloyloxy)ethyl-3-butylimidazolium bis(trifluoromethane sulfonyl)imide ...(IMMATFSI)/bisfluorosulfonylimide (IMMAFSI) or 1-(2-methacryloyloxy)ethyl-1-methylpyrrolidinium bisfluorosulfonylimide (PYRMAFSI)/bis(trifluoromethane sulfonyl)imide (PYRMATFSI) in the presence of bis(trifluoromethane)sulfonamide (LiTFSI) solutions at different concentrations in either 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIFSI), 1-ethyl-3-methylimidazolium bis(trifluorosulfonyl)imide (EMITFSI) or
N
-propyl-
N
-methylpyrrolidinium bis(fluorosulfonyl)imide (PMPFSI). The resulting IGPs are thermally stable, easy-to-handle solids wherein the overall ionic conductivity ranges from about 1 to about 10 mS cm
−1
at 25 °C. The diffusivity of the ions Li, FSI and TFSI was studied at 25 °C by PGSE-NMR. In IGPs containing imidazolium groups both in the polycationic scaffold and the ionic liquid phase, their large Li ion diffusivities (up to 40 × 10
−12
m
2
s
−1
, well above that of the anions) suggest the existence of an important contribution of anion exchange Li transport. To a lesser extent anion exchange may also be occurring in IGPs containing pyrrolidinium groups in the polycationic scaffold and imidazolium groups in the ionic liquid phase and to an even lesser extent in those IGPs with pyrrolidinium in both the polyelectrolyte and the ionic liquid phase. Because of the dimensional and thermal stabilities of IGPs, safety of their components, and their large Li-ion diffusivity, these types of electrolytes appear as excellent candidates for Li and Li-ion batteries.
Ion Gel Electrolytes (IGPs) have been prepared with polycationic imidazolium or pyrrolidinium scaffolds and LiTFSI solutions in imidazolium and pyrrolidinium ionic liquids. IGPs with imidazolium groups show very large Li ion diffusivities suggesting an important contribution of anion exchange Li transport.
The fabrication of functional surfaces based on arrangements of metallic nanoparticles (MNPs) is challenging for biomedical, optoelectronic, and catalytic applications. Herein, the fabrication of 3D ...nanostructured microfibers is reported by the controlled cooperative precipitation of MNPs on electrospun polymer fiber mats, at the critical solution temperature of a thermoresponsive copolymer coating the MNPs surface. To obtain the metallic decorated surfaces, several factors must be taken into consideration, such as the previous functionalization of the metallic nanoparticle surface and the selection of a suitable polymer concentration, pH, and temperature. The results show that the plasmonic properties of the prepared surfaces depend on the solution temperature. Among potential applications, the high specific area of the resulting Au@polymer@fiber nanocomposites is ideal to be exploited for catalytic applications. Thus, the reduction of 4‐nitrophenol has been studied as a model.
Nanostructured surfaces based on metal NPs are achieved by the controlled precipitation of thermoresponsive polymer–metallic nanoparticle arrays onto electrospun fiber mats. This strategy opens up a new avenue for the preparation of nanomaterials, which high specific surface is ideal for catalytic applications.
A series of gradient and block copolymers, based on 2‐(2‐methoxyethoxy)ethyl methacrylate (MEO₂MA) and tert‐butyl acrylate (tBA), were synthesized by atom transfer radical polymerization (ATRP) in a ...first step. The MEO₂MA monomer leads to the production of thermosensitive polymers, exhibiting lower critical solution temperature (LCST) at around room temperature, which could be adjusted by changing the proportion of tBA in the copolymer. In a second step, the tert‐butyl groups of tBA were hydrolyzed with trifluoroacetic acid to form the corresponding block and gradient copolymers of MEO₂MA and acrylic acid (AA), which exhibited both temperature and pH‐responsive behavior. These copolymers showed LCST values strongly dependent on the pH. At acid pH, a slightly decrease of LCST with an increase of AA in the copolymer was observed. However, at neutral or basic conditions, ionization of acid groups increases the hydrophilic balance considerably raising the LCST values, which even become not observable over the temperature range under study. In the last step, these carboxylic functionalized copolymers were covalently bound to biocompatible and biodegradable films of poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) P(HB‐co‐HHx) obtained by casting and, previously treated with ethylenediamine (ED) to render their surfaces with amino groups. Thereby, thermosensitive surfaces of modified P(HB‐co‐HHx) could be obtained.
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