C. Uriarte

Inverse gas chromatography in the characterization of polymeric materials

Different experimental results are presented for the use of inverse gas chromatography in the determination of the physico-chemical properties of pure polymers, polymer solutions and polymer blends. Using poly(hydroxy ether of bisphenol-A) (Phenoxy), its solutions and its blends with other polymers, thermal transitions, polymer solubility parameters, polymer-solvent and polymer-polymer interaction parameters and diffusion coefficients of small molecules in pure Phenoxy have been measured by inverse gas chromatography.

Polymer–solvent interaction parameters in polymer solutions at high polymer concentrations

Molecular mass and temperature dependences of the polymer-solvent interaction parameter have been investigated in the extreme interval of high polymer concentration using inverse gas chromatography (IGC). The observed molecular mass dependence has been compared with the predictions of a theoretical model, which emphasises the role of intramolecular contacts in the polymer chain. The model reproduces reasonably well the molecular mass dependence. However, enthalpic and entropic contributions of the interaction parameter, obtained from IGC measurements at different temperatures, exhibit behaviours difficult to explain in the framework of the current models.

Carbon dioxide transport properties of composite membranes of a polyetherimide and a liquid crystal polymer

Abstract The effect of the addition of a liquid crystal polymer (Rodrun) on the gas sorption and transport properties of a polyetherimide (PEI, Ultem 1000) was investigated. CO 2 permeation and sorption measurements were made with films of PEI, Rodrun and heterogeneous PEI/Rodrun blends at different pressures and temperatures. In all cases, permeability, diffusion and sorption coefficients decreased when the amount of Rodrun increased. A good agreement was found when permeability data obtained using both a permeability cell and a Cahn electrobalance were compared. Permeabilities of the binary composite material were calculated on the basis of those of the pure components and some theoretical assumptions concerning blend morphology. Results were consistent with a Rodrun structure in the composite intermediate between a fibrillar and a laminar morphology, as electron microscopy evidenced experimentally.

Determination of the interaction parameter g by inverse gas chromatography: an additional experimental test of the classic lattice model

Abstract Inverse gas chromatography measurements on narrow polystyrene samples of different molecular weights have been interpreted in terms of the classic lattice model. The analysis includes a rather complex temperature dependence of the interaction parameter, g, different from the usual Flory-Huggins prediction, which only allows a linear dependence on 1 T . The extension of the simple model supplies an adequate description of the data, giving the enthalpic and entropic contributions of the interaction parameter at infinite dilution, g∞. The different coefficients of the new temperature dependence have been determined from experimental data obtained by using chromatographic columns packed with polystyrene samples of different molecular weights, where different molecular probes have been injected. The influence of the molecular weight on these coefficients has also been studied.

Chromatographic studies of a poly(vinyl methyl ether)/phenoxy resin blend near the lower critical solution temperature

Abstract A blend of poly(vinyl methyl ether) and poly(bisphenol A hydroxy ether) was studied by means of inverse gas chromatography in the vicinity of the lower critical solution temperature. The comparison of the specific retention volume of the mixed polymer system with the average value of the specific retention volumes of the pure components allowed for the detection of the phase separation, which was in reasonable agreement with the phase diagram determined by optical microscopy. Interaction parameters at the cloud-point temperature were negative and far from the critical value obtained from the phase-separation data. They were also probe-dependent. The results have been interpreted on the basis of a ternary gT parameter similar to that employed in ternary systems of one polymer and two solvents.

Estimation of interaction parameters of a poly(hydroxy ether of bisphenol A)/poly(vinyl methyl ether) blend by inverse gas chromatography

Abstract A blend of poly(hydroxy ether of bisphenol A) (phenoxy) and poly(vinyl methyl ether) (PVME) was investigated by inverse gas chromatography (i.g.c.) over a wide temperature range. Specific retention volumes were measured for a variety of probes in pure and mixed stationary phases and interaction parameters were calculated. It was found that the polymer-polymer interaction parameter was probe-dependent. Two methods of data analysis recently proposed were applied in an attempt to eliminate this dependence. In both cases similar results were obtained with similar and large confidence intervals. I.g.c. experimental results were compared with theoretical calculations of an association model for polymer mixtures with specific interactions. A reasonable agreement was found.

Gas chromatographic measurements of solute diffusion in blends of phenoxy and poly(1,4-butylene adipate)

Abstract The infinite dilution diffusion coefficients of n-octadecane in poly (hydroxy ether of bisphenol A, Phenoxy), poly (butylene adipate, PBA) and a 50:50 blend were studied using inverse gas chromatography (IGC). Measurements were performed at different temperatures above the thermal transitions of the stationary phases. A blend diffusion coefficient lower than that predicted by the linear logarithmic mixing rule was observed. The experimental results were analyzed using free volume and activated state theory concepts. Experimental data at zero flow rate were used in the calculation of the free energy density B, which accounts for the polymer-polymer interaction in the blend.

Interaction energies in polymer/polymer mixtures

Abstract In the application of the lattice fluid theory to explain and simulate thermodynamic functions and phase diagrams of polymeric mixtures involving both homo- and copolymers, the only adjustable parameter is the so-called characteristic interaction energy density ΔP∗. In this paper, we present a test of consistency between the ΔP∗ values obtained from phase diagrams and from retention specific volumes determined by inverse gas chromatography. Measurements have been done on a blend of poly(vinyl methyl ether) and poly(hydroxy ether of bisphenol A), which exhibits an LCST-type phase diagram. The previously reported ΔP∗ temperature dependence seems to be verified. Another interesting conclusion is the dominant role played by ΔP ∗ in the thermodynamic functions describing the miscibility of the mixture.