Solution Properties of Polyurethanes Studied by Static Light Scattering, SEC-MALS, and Viscometry

Solution behaviour of PUs of different composition in DMF, LiBr/DMF, and THF was studied by a static light scattering (LS), size exclusion chromatography coupled to a multi-angle light scattering (SEC-MALS), and viscometry. The influence of PU chemical composition, kind of a solvent, and addition of simple salts on PU hydrodynamic volume was investigated. The values of the second virial coefficient (A2) determined by LS measurements indicated that THF is a better solvent for the flexible soft segments, whereas LiBr/DMF is better for the hard segments in the PU chains. Since the A2 values of PUs indicated that LiBr/DMF is a worse solvent than THF, the hydrodynamic volumes of all investigated PUs were smaller, as indicated by smaller values for the radius of gyration (Rg) and intrinsic viscosities [η] of PUs in LiBr/DMF. The PU molar mass averages and Rg determined in THF (LiBr/DMF) were comparable regardless of the method used (LS or SEC-MALS) and did not depend on solution concentration, indicating that PUs were disolved on a molecular level. In DMF, peculiar dilute solution behaviour was observed for all PUs investigated. The PU molar mass averages, Rg, and [η] were higher than those determined in LiBr/DMF indicating that the PUs in DMF associated to a certain degree dependent on the chemical composition of PU.