Combination of SEC/MALS experimental procedures and theoretical analysis for studying the solution properties of macromolecules

Size-exclusion chromatography (SEC) with dual detection, i.e., employing refractive index (RI) and multiangle light-scattering (MALS) detectors, has been applied to study the solution properties of two very different polymer–solvent systems at 25 °C: poly(N-vinylcarbazole) (PVCz) in an organic solvent THF that is a very good solvent and a system under θ conditions that is formed by polyvinylpyrrolidone (PVP) in water containing a 0.1 M concentration of NaNO3. In both cases, the analysis of a single highly polydisperse sample obtained by free radical polymerization is enough for obtaining molecular weight and radius of gyration calibration curves, molecular weight distributions (MWD) (and thus, molecular weight averages), molecular dimensions, scaling laws coefficients and unperturbed dimensions. Extrapolation to θ conditions produces values of the characteristic ratio of the unperturbed dimensions Cn=〈r2〉o/nl2=15.9 and 14, respectively, for PVCz and PVP. Unperturbed dimensions are also theoretically calculated with different models such as Kuhn equivalent chain, worm-like chain and rotational isomeric states model. Conformational parameters required for this last model were taken from the literature in the case of PVCz; however, they are calculated by molecular dynamics simulations in the case of PVP. Theoretical values obtained with the RIS model are in good agreement with the experimental results.