Ileana Recalde

Preferential solvation of a dicyanate ester monomer and poly(sulfone) in different organic solvents by size-exclusion chromatography☆

Preferential solvation parameters A in the ternary systems solvent (1) -monomer (2) -polymer (3) were determined as a tool to measure the compatibility between the cyanate ester monomer Arocy B10 and poly(sulfone), PSF, in the presence of three organic solvents: tetrahydrofuran, dimethylformamide and dicloromethane. The A parameter was measured by size-exclusion chromatography at different monomer-to-polymer ratios. The quantitative evaluation was rigorously made at polymer-diluted conditions. PSF was found to be preferentially solvated by the monomer. Concerning the solvent used, systems containing tetrahydrofuran showed the strongest solvation, the lowest A values being those obtained in dicloromethane. These results were in accordance with the intrinsic viscosity values of the PSF-solvent systems. The variation of A values with the Arocy B10 concentration is strongly dependent upon the nature of the solvent.

Quantitative Evaluation of the Swelling and Crosslinking Degrees in Two Organic Gel Packings for SEC

Full Paper: The elution behavior of different solvent/ polymer systems has been studied by means of size-exclusion chromatography (SEC) in two organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, named l-styragel and TSK-Gel HHR. Both packings offer similar characteristics (pore size, particle size, efficiency) but some differences arise when eluting the same systems. The different elution behavior observed in both polymeric gels has been analyzed in terms of their swelling and crosslinking degrees. To evaluate the magnitude of these parameters, a new equation is proposed which has been derived from the Flory-Huggins theory of swelling equilibrium, and takes into account binary and ternary thermodynamic interaction functions. The equation appropriately predicts the experimental results, showing that the gel that exhibits more solute-packing attractive interactions (or adsorption as secondary mechanism) is also the one with the highest crosslinking degree or lowest swelling ratio. In this sense, the l-styragel column was the most crosslinked polymer network. In addition, the influence of solvent nature, polymer nature, and solute composition on the observed swelling degree has also been compared in both packings.

A Qualitative Analysis of Secondary Mechanisms in SEC of Polymers Through the Mean Value of the Viscosimetric Exponent

Abstract Size exclusion chromatography (SEC) universal calibration curves for poly(dimethylsiloxane), polybutadiene and poly(2-vinylpyridine) samples have been obtained in columns packed with cross-linked polystyrene gel using cyclohexane, toluene, benzene, dioxane and tetrahydrofuran as eluents at 25°C. The eluents exhibit different thermodynamic quality for the polymeric solutes and for the gel matrix which is reflected in the values of their Mark-Houwink-Sakurada exponents a. The plots of log(hydrodynamic volume) versus retention volume for the polymeric solutes in different eluents are displaced to higher retention volumes than that of THF-polybutadiene (ideal SEC), evidencing the existence of secondary mechanisms. This elution behavior could be qualitatively explained through the mean average value ā, but a quantitative analysis requires the knowledge of solute—solvent, solvent—gel, solute—gel and ternary interaction parameters.

Miscibility and kinetic behaviour of cyanate resin/polysulfone blends

A dicyanate ester resin was modified by blending with polysulfone (PSF) and cured at different temperatures with or without cobalt catalyst. Size exclusion chromatography was used to determine the cyanate conversion until the gel point. The morphology of the cured samples, characterised by scanning electron microscopy, varied from PSF particle structure to a combined particle structure.

Effect of conductivity of hole injection layer on the performance of a blue light emitting solution processable OLED

The performance of blue emitting OLED devices, using a polyspiro as blue light emitting polymer, were studied as a function of the conductivity of a novel hybrid hole injection material. The hole injection material is based on a polyarylamine using a molecular magnet as oxidant. The charge density and the luminance of the devices changed considerably with increasing conductivity of the hole injection layer. The change in device performance can be attributed to a change from a hole limited device to a balanced charge carrier device and eventually to an electron limited device. The performance of the optimized device configuration is significantly improved with respect to a device making use of PEDOT:PSS as the hole injection layer reaching efficacies of 3.5 cd/A at 5000 cd/m2.

Isothermal Curing of a Dicyanate Ester Monomer Up to the Gel Point as Studied by Size Exclusion Chromatography

Abstract The curing of a dicyanate ester of bisphenol A with and without cobalt(II) acetylacetonate/nonylphenol and with copper(II) acetylacetonate/nonylphenol catalysts was analyzed until the gel point using size exclusion chromatography (SEC). This technique can be used to determine the overall dicyanate conversion as a function of time in the pre-gel state at different curing temperatures (between 130°C and 220°C according to the system). The results have been compared with those obtained by curing the same system by differential scanning calorimetry, showing good agreement. The data obtained indicate that the rate of reaction in the pre-gel stage is kinetically controlled and can be fitted with a second-order reaction with respect to the disappearance of cyanate groups. Apparent activation energies in the range 69–72 kJ/mol have been obtained from the rate constants. Experimental data on gelation times give activation energies around 70–77 kJ/mol, in accord with previous values.