Tuning nanophase separation behavior in segmented polyhydroxyurethanes via judicious choice of soft segment

Segmented polyurethanes (PUs) are composed of alternating sequences of soft and hard blocks. Depending on the composition of these blocks, they can exhibit properties ranging from soft elastomers to hard plastics while retaining the processing characteristics of thermoplastics. The soft blocks are typically long, flexible molecules with a glass transition temperature (T_g) below room temperature while the hard blocks have a T_g above room temperature and are composed of diisocyanate condensed with small molecule diol. Segmented PUs typically exhibit excellent nanophase separation due to the incompatibility between the soft and hard domains as well as the hydrogen bonding between polar urethane units in the hard domain. Varying degrees of nanophase separation are expected depending upon the structures of diisocyanates, soft segments, and chain extenders as well as overall material compositions.^1,2