Brønsted-Acid-Catalyzed Exchange in Polyester Dynamic Covalent Networks.

The effect of catalyst strength on polyester-alcohol dynamic covalent exchange was systematically studied using Brønsted acids and a low-Tg poly(4-methylcaprolactone) vitrimer formulation. Relaxation times, activation energies, and Arrhenius prefactors are correlated with pKa. Strong protic acids induce facile network relaxation at 25 °C on the order of 104-105 s, significantly faster than Lewis acid alternatives that function only above 100 °C. Activation energies span 49-67 kJ/mol and increase as pKa decreases. The opposite trend is observed with the Arrhenius prefactor. We anticipate that the quantitative understanding of Brønsted acid effects disclosed herein will be of utility in future studies that exploit acid-catalyzed dynamic covalent bond exchange.