0000000000194122
AUTHOR
Rosa García-lopera
showing 16 related works from this author
Miscibility of a DGEBA Based Epoxy Resin Blended with Thermoplastic Mixtures of Poly(styrene) and Block Copolymers: Influence of the Copolymer Conten…
2008
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 obtai...
Separation Efficiency of Two SEC Packings: Comparison of Chromatographic, Thermodynamic, and Fractal Parameters
2004
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…
Size‐Exclusion Chromatography in Single and Mixed Eluents: Effects of Sorption of Solvent and Polymer Solutes on Novel TSK‐Gel Super AW Columns
2005
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 th…
A thermodynamic approach to study hydrogen-bonding interactions in solvent/solvent/polymer ternary systems
2007
Abstract A thermodynamic approach based on both the classical Flory–Huggins (FH) formalism and the association equilibria (AE) theory has been developed to study the solubility properties of a system formed by a proton-donor solvent (A), a proton-acceptor solvent (B) and a proton-acceptor polymer (C). The miscibility of this ternary system is attained by competitive specific interactions via hydrogen-bonding established between the hydroxyl and carbonyl interacting groups of either solvent–solvent (AB) or solvent–polymer (AC) system components. The binary AB and AC specific interactions and their dependence with the system composition as well as with the extent of the association equilibriu…
Modelling the hydrogen-bonding interactions in a copolymer/biodegradable homopolymer blend through excess functions
2008
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 multi- component 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 hydrogen- bonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the car- bonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self- association of PSVPh and specific interacti…
The Fractal Approach to Secondary Mechanisms in SEC
2007
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…
Size-Exclusion Chromatographic Determination of Polymer Molar Mass Averages Using a Fractal Calibration
2005
The characterization of polymers by size-exclusion chromatography basically consists of the determination of the weight-average molar mass (Mw), number-average molar mass (Mn), and polydispersity index (I). An accurate estimation of these magnitudes requires the use of a reliable and trusted calibration curve. Three procedures for building up a calibration curve are analyzed in this work. The first is the classical universal calibration (UC), based on the elution of tetrahydrofuran-polystyrene in a system as reference. The second is based on the proper calibration curve made with standards of the sample under study. However, two main drawbacks arise when using these methodologies: the nonfu…
The fractal calibration method applied to the characterization of polymers in solvent mixtures and in mixed gel packings by SEC.
2007
The size-exclusion chromatographic (SEC) behaviour of different solvent/polymer systems in three packing sets has been analysed from fractal considerations. The three-column sets studied are specifically formed by: (i) 'pure' micro-styragel, (ii) 'mixed' TSK Gel H(HR + XL + HR) and (iii) mixed TSK Gel H(XL + HR + XL). The experimental data reveals that in most of the systems assayed the classical universal calibration (UC) is not fulfilled, denoting the existence of secondary effects accompanying the main SEC mechanism. In order to obtain an accurate characterization of different polymers eluted in solvent mixtures and/or mixed packings, the use of a reliable and trusted calibration curve i…
Influence of the Copolymer Content on the Miscibility, Phase Behaviour and Morphology of a DGEBA/Polystyrene/Styrene-co-Maleic Anhydride Ternary Blend
2009
The miscibility, phase behaviour and morphology of ternary systems, formed by a DGEBA-based epoxy resin, polystyrene (PS) and styrene-co-maleic anhydride (SMA) copolymers have been investigated through phase diagrams. The analysis has been done in the absence and in the presence of 4,4'-methylene bis(2,6-diethyl aniline) (MDEA) as curing agent. In both cases, the influence of the copolymer content on blend compatibility, has been discussed. The results show that miscibility is enhanced by the presence of SMA copolymer in the blend and as the MA content in the copolymer is increased (from 7 to 14wt.-%), due to specific H-bonding interactions between the H-donor hydroxyl groups on the epoxy r…
An Analysis of the Concentration Effects on Elution Volumes by Using the Preferential Solvation Parameter in Two SEC Packings
2002
Size exclusion chromatography (SEC) elution behavior of different solvent/polymer systems has been analyzed from chromatographic, thermodynamic, and hydrodynamic points of view in two organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, μ-styragel and TSK-Gel H HR . Although both packings present similar chromatographic properties, some differences arise when eluting the same systems. The values of the adsorption distribution coefficients, K p , have been correlated with the preferential solvation coefficient, λ (see Figure), for both packings, showing that those systems with lower and negative λ values (denoting higher preferential solvation of the polymer by the…
Fractal calibration in size-exclusion chromatography
2003
Abstract The elution behaviour of different polymer–solvent systems in three types of organic columns for SEC has been compared and interpreted. The experimental data show that the classical universal calibration is not accomplished. Deviations from a unique curve are observed due to the binary and ternary interactions between the components of the system (solvent, polymer and gel) which results on secondary mechanisms accompanying the main pure or “ideal” SEC separation mechanism. Both, enthalpic and entropic effects are interpreted in terms of the swelling and crosslinking degrees of the gel packings, and are also related with the fractal characteristics of their surfaces, such as the fra…
FTIR isothermal cure kinetics and morphology of dicyanate ester resin/polysulfone blends
2005
Abstract The isothermal cure of a dicyanate ester monomer by “in situ” Fourier transform infrared spectroscopy (FTIR) has been investigated. The degree of cyanate conversion and the kinetic parameters have been determined for cobalt catalyzed and uncatalyzed resin as well as for polysulfone (PSF) modified systems at different curing temperatures. The cyanate conversion increases with the increment of temperature and with the addition of a catalyst, but it does not vary with the addition of PSF. In all the systems studied, the rate of reaction showed a second-order dependence on the cyanate concentration in the kinetically controlled stage. Moreover, the addition of PSF generates a matrix wi…
Interaction of polyelectrolytes with oppositely charged micelles studied by fluorescence and liquid chromatography
2005
It is studied by spectrofluorimetry the association of ionized cationic micelles (cetyltrimethylammonium bromide, CTAB) with oppositely charged polyelectrolyte [sodium poly(styrenesulfonate), PSSNa]. CTAB provokes a change in the fluorescence intensity emitted by PSSNa. The investigated surfactants form micelle-like aggregates before critical micellar concentration (CMC). Two approaches (binding and partition equilibrium) are used to obtain the association constant, KA, number of CTAB molecules in a binding site, N, and apparent partition coefficient, Γ. Analysis of the parameters as a function of polymer concentration and ionic strength μ is performed. The effect of μ shows an enhancement …
Miscibility of Blends of Biodegradable Polymers and Copolymers with Different Plasticizers
2008
Miscibility between components of different plasticizer(A)/solvent(B)/biodegradable polymer(C) ternary systems with H-bonding has been compared. Systems were formed by two H-donor phenolic plasticizers, 4-nonylphenol (NP) and 4:4'-dihydroxydiphenylmethane (BPF); an H-acceptor solvent, epichlorohydrin (ECH); and H-acceptor poly(3-hydroxybutyrate) (PHB) or poly[(3-hydroxybutyrate)-co-(3-hydroxyvalerate)] (PHBHV) copolymers. Blend miscibility is the result of the balance of three competitive H-bondings: plasticizer self-association (AA), plasticizer-solvent (AB) and plasticizer-polymer (AC) interassociations. The strength and extent of such specific interactions have been experimentally monito…
Determination of χ from liquid-liquid phase data in ternary polymer systems (solvent/polymer/polymer) with hydrogen bonding
2008
Two different models accounting for the dependences of χ and g interaction parameters on both temperature and composition have been applied to different ternary polymer systems (TPS) solvent(1)/polymer(2)/polymer(3). The ana- lyzed TPS have consisted on ten different polymer mixtures in chloroform as common solvent that can specifically interact via hydrogen bond. Experimental ternary phase diagrams determined by liquid chromatography were taken from literature. The application of the two models to the experimental data have served to obtain χij and gij interaction parameters for all the binary ij (ij = 12, 13, 23) interactions established between the three components of the system, with si…
Study on resolution capacity and secondary mechanisms of three different TSK gels for organic SEC.
2005
A comparative study on the elution behavior in size-exclusion chromatography (SEC) of three polymeric TSK gel packings, named H, H H R , and H X L types, is performed. The deviations of the universal calibration (u.c.) curves of seven solvent-polymer systems show evidence that the existence of secondary effects accompanying the main SEC mechanism. These secondary mechanisms are a consequence of the binary enthalpic interactions between the different components of the chromatographic system, such as polymer-solvent, polymer-gel and solvent-gel. However, in the present case, the observed deviations from a unique u.c. curve can mainly be attributed to adsorption of polymeric solutes (analytes)…