Interaction of segmented polyurethanes and polyurethane‐ureas with water

Sorption of water vapor by oligomeric homopolymers and triblock copolymers of ethylene oxide and propylene oxide, and by polyurethanes and polyurethane ‐ ureas derived from them is discussed. While the sorption isotherms (plots of ψ 1 vs a 1 , where ψ is he volume fraction of sorbed water and a 1 is activity) for most polymers investigated here are smooth and convex towards the abscissa, those found with polyurethane‐ureas containing long hard blocks have a “toe” at low activities. The plots of a 1 /ψ 1 vs a 1 are shown to facilitate the analysis of data and the interpretation in terms of the D'Arcy‐Watt theory. Smooth isotherms are fitted by a simple equation with two parameters. The first is related to the limiting value, χ 0 , (at ψ 1 → 0) of the χ parameter characterizing the polymer‐water interaction. The dependences of χ 0 on the polymer composition (content of hard segments or oxyethylene units) can provide information on the interaction between hard and soft segments. The second parameter is used in the computation of parameters characterizing the clustering tendency of water molecules. This tendency depends mainly on the content of oxypropylene units but is also raised by urethane or urea groups, though not so much as by oxypropylene groups.