Acid‐Mediated Autocatalysis in Vinylogous Urethane Vitrimers
AbstractVitrimers are a class of polymeric materials with outstanding properties. Intramolecular substitution reactions lead to a dynamic exchange within the polymer network which enables thermoreversible stress relaxation in yet permanently crosslinked materials. In this paper, the acid‐mediated autocatalysis is explored as a rearrangement pathway for vinylogous urethane vitrimers. The autocatalysis enables transimination reactions, resulting in a dynamic exchange among the enamine‐one species, without an excess of free amines. Therefore, the enamine‐ones are protonated by a Brønsted acid and turn into electrophilic iminium‐ones, thus enabling fast backward and substitution reactions with water and free amines. This work provides an in‐depth investigation of the mechanism by kinetic studies of selected compounds. In addition, novel elastomeric and thermosetting poly(vinylogous urethane) networks with and without free amine groups and additional para‐toluene sulfonic acid as a Brønsted catalyst are prepared by bulk polymerization of hexane‐1,6‐diylbis(3‐oxobutanoate) and tris(2‐aminoethyl)amine. The underlying exchange mechanisms are determined by stress‐relaxation experiments with stress relaxation times of 0.3–54 000 s at 110 °C.