Velocity sedimentation and intrinsic viscosity analysis of polystyrene standards with a wide range of molar masses

摘要

Analytical ultracentrifugation is one of the key methods among the molecular hydrodynamic methods of polymer science, biophysics, and colloid science. The aim of this work is to demonstrate the possibilities of a modern instrument, the Beckman XLI Analytical Ultracentrifuge, coupled with the now available software for the molecular characterization of synthetic polymers. For this purpose the classical system polystyrene in methyl ethylketone was investigated. The samples of low polydispersity index were studied in a 1 000-fold interval of molar mass values. The exhaustive analysis of such hydrodynamic values as velocity sedimentation coefficient, frictional ratio, concentration Gralen coefficient, and intrinsic viscosity, was done. The values of partial specific volume, refractive index increment, and hydrodynamic invariants were also determined and discussed. The estimation of the statistical segment length (or persistent length) of polystyrene chains was made taking into account the intrachain excluded volume and draining effects (Gray-Bloomfield-Hearst theory). The obtained experimental data and results of its analysis allow the conclusion that the method of velocity sedimentation, coupled with the numerical solution of the Lamm equation, represents a powerful absolute characterization method for molar mass determination of flexible polymers of low polydispersity in relatively poor solvent.