Chemical control of the viscoelastic properties of vinylogous urethane vitrimers

TLDR

Vinylogous urethane vitrimers are polymer networks that can undergo network rearrangements, stress relaxation, and viscoelastic flow via rapid addition/elimination reactions of free chain end amines. These effects were mechanistically rationalized using low‑molecular‑weight kinetic model experiments. The covalent exchange kinetics can be tuned by additives; Brønsted or Lewis acids accelerate network‑level exchange, while bases inhibit it, enabling rational design of vitrimer elastomers with a wide range of viscoelastic properties.

Abstract

Abstract Vinylogous urethane based vitrimers are polymer networks that have the intrinsic property to undergo network rearrangements, stress relaxation and viscoelastic flow, mediated by rapid addition/elimination reactions of free chain end amines. Here we show that the covalent exchange kinetics significantly can be influenced by combination with various simple additives. As anticipated, the exchange reactions on network level can be further accelerated using either Brønsted or Lewis acid additives. Remarkably, however, a strong inhibitory effect is observed when a base is added to the polymer matrix. These effects have been mechanistically rationalized, guided by low-molecular weight kinetic model experiments. Thus, vitrimer elastomer materials can be rationally designed to display a wide range of viscoelastic properties.