Metal-Free Functionalization of Linear Polyurethanes by Thiol-Maleimide Coupling Reactions

Polyurethanes (PU) are a versatile class of polymers used in today's high-performance applications. The urethane linkage imparts most of the important physical properties, leading to the suitable use of PU's in construction, automotive, flooring, and sports. A small alkyne containing diol was incorporated in linear PU chains, as well as in films and foams and these materials were subsequently reacted with a range of azide containing molecules. Thus, a thiol to maleimide molar ratio larger than unity was necessary for achieving high functionalization efficiency. This was likely due to disulfide bond formation, which is a primary side reaction in thiol Michael addition reactions. On the other hand, using 5 equiv of TG did not further improve the reaction efficiency. Hence, 2 equiv of the thiol used were sufficient to obtain a maximum conversion of more than 90%. In conclusion, a new approach for the metal-free functionalization of aliphatic polyurethanes has been explored by the combination of polyaddition and thiol-maleimide coupling.