Ema ŽagarNational Institute of Chemistry,
Laboratory for Polymer Chemistry
and Technology, Hajdrihova 19, SI-1001 Ljubljana, Slovenia. E-mail:
ema.zagar@ki.si
Abstract
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 [h]
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 [h]
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.
Key words: polyurethanes, dilute solution properties, molar mass averages, molar mass distribution, size exclusion chromatography (SEC), light scattering, viscometry