Anomalous dilute solution properties of segmented polydimethylsiloxane-polyurea copolymers in isopropyl alcohol

Abstract

Preliminary characterization of amphiphilic segmented copolymers of polydimethylsiloxane and urea 'hard blocks' was conducted by measuring isopropyl alcohol (primarily) dilute solution viscosities via capillary viscometry. The traditional data analysis techniques, which provide for extrapolation of intrinsic viscosities from these experiments, revealed that increasing concentrations of polymer produced lower reduced viscosities rather than the expected higher values. A very approximate data fit reveals negative Huggins and Kraemer constants from these analyses, which are highly unusual. In a solvent such as DMF, a similar polymer having poly(tetramethylene oxide) and urea blocks and measured with identical conditions exhibited the expected behavior, showing increasing reduced viscosities over concentrations in the same range. However, the non-linearity of the data is suggestive of much more complex hydrodynamic, or supramolecular, interactions that are not clarified by the initial research.