Polyurethane
= Polyurethane
A <polyurethane> contains repeated connections of the form $\mathrm{{-}O{-}C(=O){-}NH{-}}$. Suitable <hydroxy groups> and <isocyanate> groups can produce those connections by <polyaddition>; exactly two suitable groups per feed <molecule> give the bifunctional linear model only when competing reactions and ring closure are excluded.