The ability of a material to absorb water is an indirect measure of
its hydrophilicity. Uncross-linked PU films were dissolved in water
due to the high content of PEG segments in the PUs (39–50 wt%).
Therefore, water-swelling was measured only for the cross-linked
PU films and the results are shown in Fig. 3. The water-swelling
of the PU films decreased with increasing PTMEG content, due to
the increase in the hydrophobicity of the films. When the waterswollen
film of PU-21 was dried in an oven for 12 h, it returned to its
original size, but other dried films were cracked (PU-0) or nearly
cracked due to reduced mechanical strengths after immersion in
water. As the PTMEG content increased, the mechanical strength of
the dried PU films decreased less rapidly due to the increase in the
hydrophobicity of PU films.