The perturbed-chain SAFT equation of state is extended to heterosegmented molecules and is applied to copolymers with a well-defined (alternating) repeat-unit sequence as well as to systems with a statistical sequence of the monomers in the backbone. Copolymers with a statistical sequence of the constituting repeat units usually require an assumption on the sequence of neighboring repeat units within the chain. A simple approach for defining such repeat-unit arrangements is proposed. Systems containing polyolefine copolymers (poly(ethylene-co-propylene) and poly(ethylene-co-1-butene)) covering the complete range of copolymer composition (including both of the appropriate homopolymers) were modeled in a mixture with solvents. Good results were found for mixtures of copolymer/solvent systems using constant interaction parameters. Copolymers comprising both nonpolar and polar repeat units, for example, poly-(ethylene-co-vinyl acetate) and poly(ethylene-co-methyl acrylate), require an interaction parameter correcting the interactions between repeat units of different types, which depends on the repeat-unit composition.
The solubility of DL-methionine in pure water has been measured in a temperature range of 293.15-353.15 K by means of on-line attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. These experimental data, as well as literature data for the solubility of glycine and DL-alanine in aqueous and alcohol solutions, were modeled using the PC-SAFT equation of state. Pure-component parameters for glycine, DL-alanine, and DL-methionine were fitted to the vapor pressures and to the densities of their aqueous solutions. Only one temperature-independent binary parameter is required for each system. The solubility of amino acids in water-alcohol mixtures (ternary systems) was then predicted without fitting any additional parameters. The results of the prediction correspond well to literature data. To retrieve the pH dependency, the solubility of DL-methionine in different HCl and NaOH solutions in the pH range of 1.5-9.5 was determined via gravimetric measurements. Using the knowledge of the acid-base behavior (pK a values) of the respective amino acids, the solubility of glycine, DL-alanine, and DL-methionine in aqueous electrolyte solutions can be predicted in good agreement with the experimental data.
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