A polyester-urethane is a polyurethane containing polyester-derived segments. Its chain therefore combines urethane linkages with repeated ester functionality in another part of the polymer architecture.
The contrasting segments can create flexible regions together with more strongly interacting regions that help hold the material together. Mechanical response depends on segment lengths, chemical composition, processing and morphology. The ester-containing portions also provide possible sites for hydrolysis, so durability cannot be inferred from the urethane linkage alone. The name describes a family of architectures rather than one fixed repeating formula.
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