Rosa García-Lopera

Miscibility of a DGEBA Based Epoxy Resin Blended with Thermoplastic Mixtures of Poly(styrene) and Block Copolymers: Influence of the Copolymer Content and Chemical Nature

The miscibility and phase behavior of ternary systems formed by a DGEBA based epoxy resin, polystyrene (PS), and diblock copolymers has been investigated through phase diagrams experimentally obtained by using a light transmission device. The analysis has been done in the absence and in the presence of a curing agent. In both cases, the influence of the copolymer content and chemical nature (PS-b-PMMA or PS-b-PHEMA) has been discussed. The results show that miscibility is enhanced as the copolymer content in the ternary blend is increased, due to specific H-bonding interactions between the H-donor hydroxyl groups on the epoxy resin and the H-acceptor carbonyl groups in the copolymer, the effect being more pronounced with PMMA than with PHEMA. Experimental results have been fitted with the Flory-Huggins theoretical model by using interaction parameters depending both on temperature and composition. The morphological evolution of the epoxy networks has been examined by scanning electron microscopy (SEM).

Modelling the Hydrogen-Bonding Interactions in a Copolymer/Biodegradable Homopolymer Blend through Excess Functions

A recent theoretical approach based on the coupling of both the Flory-Huggins (FH) and the Association Equilibria thermodynamic (AET) theories was modified and adapted to study the miscibility properties of a multicomponent system formed by two polymers (a proton-donor and a proton-acceptor) and a proton-acceptor solvent, named copolymer(A)/solvent(B)/polymer(C). Compatibility between polymers was mainly attained by hydrogenbonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the carbonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self-association of PSVPh and specific interactions between the PSVPh and the H-acceptor group (an ether oxygen atom) of the epichlorohydrin (ECH) solvent were also established in a lower extension, which competed with the polymer-polymer association. All the binary specific interactions and their dependence with the system composition as well as with the copolymer content were evaluated and quantified by means of two excess functions of the Gibbs free energy, ΔgAB and ΔgAC. Experimental results from fluorescence spectroscopy were consistent with the theoretical simulations derived with the model, which could also be applied and extended to predict the miscibility in solution of any polymer blend with specific interactions.

Separation Efficiency of Two SEC Packings: Comparison of Chromatographic, Thermodynamic, and Fractal Parameters

Abstract The size‐exclusion chromatographic (SEC), thermodynamic, and fractal behavior of two organic packings, named TSK‐Gel HHR and TSK‐Gel HXL, has been compared in order to assess their separation efficiency. The different experimental elution trends of five solvent/polymer systems have been evidenced through the universal calibration curves, and the existence of secondary mechanisms (such as adsorption) has been quantified by the chromatographic partition coefficient K p. From a thermodynamic point of view, the swelling and crosslinking degrees have been evaluated and compared in the two gels assayed. Moreover, the values of some fractal parameters (fractal dimension of the surface and available pore size) provide support for the chromatographic and thermodynamic results. The comparison of all findings reveals that, in general, more solute–gel adsorption effects (higher K p values) occurs in the TSK‐Gel HXL packing due to its higher crosslinking degree, lower swelling degree, and lower fractal dimension of the surface than in TSK‐Gel HHR. In consequence, the latter packing offers a better potential resolution for polymer characterization by SEC.

Size‐Exclusion Chromatography in Single and Mixed Eluents: Effects of Sorption of Solvent and Polymer Solutes on Novel TSK‐Gel Super AW Columns

Abstract The novel TSK Gel Super AW column packing is based on a polymeric gel with residual hydrophobic and hydrophilic groups on the gel surface. These groups can act as active sites making the chromatographic support compatible both with polar and apolar eluents. This interesting property allows the elution of systems of very different polarities but also induces binary polymer–gel, polymer–solvent, and solvent–gel enthalpic interactions that lead to a mixture of separation mechanisms: repulsion, partition, or adsorption besides the main size‐exclusion chromatography (SEC) mechanism. For this reason, the elution behaviour of many and diverse polymer/solvent systems has been studied in these columns. Depending on the chemical nature of the polymeric solutes and/or the thermodynamic quality of the eluents (pure and mixed solvents), the universal calibration curves deviate from that of a reference system, which is supposed to elute according to an ideal SEC mechanism. The observed deviations have been qualitative and quantitatively explained in terms of the predominant binary interactions, and therefore, in the light of the secondary mechanisms present in the separation process.

The Fractal Approach to Secondary Mechanisms in SEC

Abstract Size‐exclusion chromatography (SEC) is one of the most used experimental techniques to characterize polymers in solution; it has been applied to interpret the elution behaviour of many polymer‐solvent systems in five types of column packings. The experimental data have revealed that the classical universal calibration is not accomplished. Deviations from a unique curve are a consequence of two effects: entropic (exclusion by size) and enthalpic (binary and ternary interactions between solvent, polymer, and gel), which results in secondary mechanisms accompanying the main “ideal” SEC separation mechanism. Therefore, three approaches of building a calibration curve have been compared in this work: (i) the classical universal calibration based on the elution of tetrahydrofuran (THF)‐polystyrene (PS) system as reference; (ii) the specific or proper calibration curve made with standards of the sample under study; and (iii) the fractal calibration. The understanding of the secondary mechanisms has been based on the fractal characteristics of the porous gel surfaces, as well as on the swelling and crosslinking degrees. The global analysis of data has allowed us to propose an alternative relationship between the fractal dimension, D f , and the chromatographic distribution coefficient, K D , independently of the chemical nature of the solvent, polymer, and gel. From a quantitative point of view, the fractal methodology considerably reduces the deviations found when estimating polymer molar masses by SEC.