Electrochromic properties of poly(alkoxy-terthiophenes): an experimental and theoretical investigation

Much effort has been made to synthesize novel compounds and enhance the optical properties of poly(terthiophenes). The electrochromic properties of poly(4,4′′-dimetoxy-3′-methyl-2′-5′,2′′-terthiophene) (PDMMT) and poly(4,4′′-dipentoxy-3′-methyl-2′-5′,2′′-terthiophene) (PDPMT) have been studied focusing on the differences in the alkoxy-group length. Theoretical calculations were employed to elucidate the structural and thermodynamic stability of the monomers and dimmers. The results showed that in this type of thiophenes large alkoxy chains assist positive charge dispersion through hyperconjugative effect. Thus, PDPMT is thermodynamically more stable than PDMMT in the oxidized state, leading to better electrochromic stability and optical memory.     

Porous nanocomposite hydrogel of vinyled montmorillonite-crosslinked maltodextrin-co-dimethylacrylamide as a highly stable polymer carrier for controlled release systems

Nanocomposite hydrogel consisting of dispersed montmorillonite-crosslinked maltodextrin-co-dimethylacrylamide (malt-dex-co-DMAAm) as a highly stable device was developed. Carbon-carbon π-bonds issued from glycidyl methacrylate (GMA) were incorporated onto both the MMT (MMT-π) and the malt-dex (malt-dex-π) structures. The nanocomposite copolymer hydrogel was processed via radical crosslinking reaction of malt-dex-π with MMT-π in the presence of DMAAm. The radical reaction of the carbon-carbon π-bonds at the MMT-π was verified by treating the MMT-π with sodium persulfate. There was an excellent dispersion of the MMT-π at the interior of the matrix even after the nanocomposite hydrogel being swollen, demonstrating that the developed methodology can imprint stability of mineral nanoparticles into a porous polymer network preventing diffusion of water-bonded silicate platelets toward the outside matrix. The water absorption profile became more dependent on the polymer relaxation for mineral-loader nanocomposite hydrogels. Higher water absorption had an impact on reduction of elasticity modulus due to softer polymer network in swollen state.     

Cortisol and cortisone as test substances for the efficiency of an inlet system

The results of a recent report on the use of cortisol and cortisone as test substances for inlet systems have been contradicted. The ion appearing at [M - 60]+ in the spectrum of each ofthese compounds has been shown to arise initially from an electron-impact process rather than by pyrolysis and subsequent ionization of the molecular compound. Only at higher temperatures isa significant degree of pyrolysis observed.     

Transport properties of ephedrine hydrochloride through poly(vinyl alcohol) matrices—a simple method for enantiomeric differentiation

Equilibrium and transport properties have been investigated of ephedrines, a class of sympathomimetic amines, through cryogel membranes of poly(vinyl alcohol) (PVA). The effect of the PVA (10 to 18 % (w/v)) on the release properties of (1S,2R)-(+)-ephedrine hydrochloride has been discussed on the basis of partition–diffusion and power-law models. The effect of PVA concentration on the swelling degree of PVA–ephedrine matrices have been measured, allowing the estimation of the volume fraction of polymer in the gel. Ephedrine release rate constants, computed by using a first-order kinetics approach, have been modeled by using free-volume and hydrodynamic-scaling models. Differences in the release properties of the ephedrine isomers, (1S,2R)-(+)- and (1R,2S)-(?)-ephedrine as their hydrochlorides, have also been studied at different temperatures. The release kinetic constants and the corresponding activation energies show a marked discrimination between the two ephedrine isomers. This suggests that PVA cryogel membranes possess high potential for enantiomeric differentiation.     

Low coercive field and conducting nanocomposite formed by Fe3O4 and poly(thiophene)

Magnetite and poly(thiophene) composites have been produced by in situ monomer oxidation. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) confirmed the presence of Fe₃O₄ as particle agglomerates ranging from 15 to ca. 54 nm in size. Transmission electron micrographs (TEMs) revealed a face-to-face structure in both the pure magnetite and the nanocomposite. Typical superparamagnetic (ferrimagnetic) curves have been observed, whereas the relatively weak magnetic field employed in measurement, 200 Oe, was sufficient to split the curves completely. Zero field cooling (ZFC) and field cooling (FC) curves coincide only above room temperature, indicating that the characteristic blocking temperature (T_B) for superparamagnetic particles in this assembly is above room temperature.     

Birefringent hydrogels based on PAAm and lyotropic liquid crystal: Optical, morphological and hydrophilic characterization

In this work, hydrogels of polyacrylamide (or PAAm) with confined lyotropic liquid crystal (potassium laurate-decanol-water, KL-DeOH-H₂O) (or LLC) were synthesized. The hydrogels were characterized by polarized optical microscopy (POM), refractometry, optical transmission, scanning electron microscopy (SEM) and small angle X-ray scattering (SAXS). Besides these techniques, the hydrophilicity of hydrogels was characterized by the degree of swelling. Based on POM, it was observed that the texture of the birefringent hydrogels obtained depends on their cross-linking density, and that it is formed soon after hydrogel synthesis. Refractometry results indicated an behavior antagonist to that obtained for the system constituted by thermotropic liquid crystal inserted into the PAAm lattice in relation to the dependence of Δn on the AAm concentration and the optical transmittance. SEM micrographs show that birefringent hydrogels present rougher surface when compared to the surface of PAAm hydrogels. For the same AAm concentrations, it was observed that the hydrogels with confined LLC present larger swelling values (Q) when compared to those of PAAm hydrogels. The loss of water by birefringent hydrogels is twofold slower than that of PAAm hydrogels. Hydrogels formed by PAAm and lyotropic liquid crystal synthesized in this work can be potentially used in optical devices.     

Mathematical model for the prediction of the overall profile of in vitro solute release from polymer networks

The loading of solutes onto and their release from hydrogel-based devices can be better understood when they are treated as a partition phenomenon. Partition activity (alpha) is a parameter that determines the existence of partition phenomena. It expresses the physical chemical affinities of the solute between the solvent and hydrogel phases. When alpha=0, there is no release of the solute from the hydrogel; however, if alpha>0, there is partitioning of the solute between the solvent and the hydrogel phases, and release of the solute from the hydrogel can be observed. The mathematic model proposed here predicts the overall release profile of vitamin B(12), methylene blue (MB), and acid orange 7 (AO) from semi-interpenetrating network (semi-IPN) hydrogels composed of PNIPAAm and PAAm. Experimental release tests demonstrated that alterations on variables of the system change both the released fraction and the release rate of such solutes, confirmed by the changes on values of alpha (an equilibrium parameter) and k(R) (an kinetic parameter). The modeling of solute release describes the alpha effects on release of the solute from polymer networks. The solute release mechanism is viewed here as a diffusional transport process and as a partition phenomenon. The partitioning of the solutes occurs between the solvent phase and the hydrogel phase, and the possible physical chemical affinities of the solute between hydrogel and solvent are considered.     

Solid-state radical grafting reaction of glycidyl methacrylate and poly(4-methyl-1-pentene) in supercritical carbon dioxide: surface morphology and adhesion

Solid-state radical grafting of glycidyl methacrylate (GMA) onto poly(4-methyl-1-pentene) (PMP) was performed using supercritical carbon dioxide (scCO(2)) impregnation technology. The polymer films were firstly impregnated in the scCO(2) phase with the GMA using benzoyl peroxide as thermal initiator. The grafting degree and surface morphology of the samples may be controlled by the following factors: time, temperature, and pressure of impregnation. A 2(3) factorial design to evaluate the main and interaction effects of such factors on the grafting of the PMP by GMA (grafting response) was elaborated from FTIR data. The superior and inferior limits of the levels were defined on basis of a P-x-y diagram for binary system CO(2)+GMA that provided the location of the transition curves of such a system. Better grafting response was obtained for pressure of 130 bar, temperature of 70°C and time of 7h. The PMP-g-GMA films exhibited a thermal profile similar to that of the unmodified polymer. Adhesion characteristics of polymer films are dependent on grafting degree of GMA.     

Synthesis of a thermosensitive surface by construction of a thin layer of poly (N-isopropylacrylamide) on maleimide-immobilized polypropylene

Thermosensitive surfaces were developed by the grafting of a thin layer of PNIPAAm through an UV-induced photopolymerization reaction of vinyl monomers with a free radical-activated polypropylene (PP) surface. PNIPAAm layer covering the PP surface corrected, to some extension, both depressions and fissures of the previously modified PP surfaces. The layered surfaces have morphological characteristic different from those of the non-layered surfaces, and their thickness was dependent on irradiation time. Water contact angles of the layered surfaces revealed a transition at approximately 33.5-36.5 °C as a result of a response to the variation of temperature. There was an increase in the values of the contact angles with an increase in temperature from 26 °C to 44 °C, revealing the nature both hydrophilic and hydrophobic of the surfaces due to a conformational rearrangement of PNIPAAm exposing its isopropyl groups to the liquid drop. This work offers a chemically stable thermosensitive surface (because it is covalently structured) with great potential for use as sensors and actuators.     

Degradation of polyisoprene induced by chloranil

The aim of this work was to study the degradation of polyisoprene and polybutadiene in the presence of chloranil (tetrachloro-1,4-benzoquinone). The influences of polymer concentration, chloranil concentration and temperature were evaluated using a 2³ factorial design. The efflux times of toluene solutions containing different polymer and chloranil contents at 25, 45 and 65 °C were measured, using a Ubbelohde viscometer. When high concentrations of polymer and chloranil were used, at 65 ° C, the efflux time decreased to approximately 10% of its initial value after 7 min, and, after 250 min, the efflux time reduced to approximately 50% of its initial value. The efflux time of polybutadiene solutions containing chloranil did not decrease with the reaction time. ¹H NMR of polyisoprene and polybutadiene, dissolved in CDCl₃ containing chloranil, were used to evaluate the changes in polymer unsaturation. ¹H NMR measurements showed an exponential decrease in the area for peaks due to the hydrogen bound to the unsaturated carbon in polyisoprene solutions. These results suggest the occurrence of degradation of polyisoprene. Using the same conditions, it was observed that polybutadiene degradation did not occur. Thus, it was concluded that the methyl group in polyisoprene is very important in the degradation in the presence of chloranil.