Distribution coefficients and diffusivities in three polymers for nineteen aqueous nonvolatile solutes

Abstract

Experimental results at 25°C are reported for infinite‐dilution distribution coefficients for 19 nonvolatile solutes between aqueous solution and three kinds of polymer films, and for their diffusion coefficients in the polymer matrix. The experiments were performed by coupling UV spectroscopy and gravimetric measurements with mass balances. The solutes are aromatic nonvolatile compounds that are of interest in environmental technology and may serve as model compounds for drug‐delivery systems. The polymers are ethylene‐vinyl acetate copolymers with 33 (EVAc33) and 45 (EVAc45) weight percentage vinyl acetate, and poly(vinyl acetate) (PVAc) widely used in drug‐delivery devices. For PVAc, a long time is required to reach equilibrium. Because the required time is too long for reasonable experimental studies, equilibrium distribution coefficients were calculated from finite‐time data by using a diffusion model. The contribution of surface adsorption is shown to be negligible. Infinite‐dilution distribution coefficients Ks, defined as the volume fraction of solute in the polymer divided by that in water, tend to increase with vinyl acetate content; they range from near unity to several hundred. Diffusion coefficients, determined from time‐dependent sorption data, are significantly larger in EVAc copolymers (10−10 to 10−8 cm2/s) than in PVAc (10−12 cm2/s). These data may be useful for design of membrane processes, for controlled delivery of drugs, and for application in packaging and storage of food, chemicals, and pharmaceuticals. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2041–2052, 2002

Examination of data relating to the thermodynamic and kinetic interactions between nonvolatile aqueous solutes and three ethylene–vinyl acetate copolymers

“…The intercepts of the interaction models roughly approximate the materials' intrinsic interaction capacity, with the larger intercept reflecting a material that will interact with solutes to a greater extent. The trend observed (PVAc > EVAc45 > EVAc33) matches that discussed by the authors of the previous investigation 6…”

“…The experimental details associated with the generation of the films and the measurement of the distribution coefficients and diffusivities are described elsewhere 6. No additional experimental work was performed for this article.…”

“…This is true because several of the model solutes, most notably benzoic acid (p K a = 4.21) and pyridine (p K a = 5.2), will be in their dissociated form (nonbinding form) at the solution pH used in the interaction study (5.5–6.0 per ref. 6). The relationship between a solute's interaction constant and solution pH can be expressed as follows:9 where K s,i is the distribution coefficient at the measured pH (ionized form) and K s,u is the coefficient for the neutral form of the solute.…”

“…The thermodynamic and kinetic interaction properties (distribution coefficients and diffusivities) of 19 nonvolatile solutes with three vinyl acetate type materials were recently reported 6. Although the authors of the work noted a qualitative relationship between the observed behavior of the test solutes and the solutes' lipophilicity, the nature of the relationship was not quantified.…”

Solubilities of nonvolatile solutes in polymers from molecular thermodynamics

“…We have recently measured infinite-dilution distribution coefficients for these solutes between water and polymer (Fornasiero et al, 2001). Table 1 presents the most relevant solute properties: molecular weights, densities and melting points.…”