Fig. 1. Influence of external catalysis on viscoelastic properties of vitrimers. (a) Catalysed transesterification between alcohol and ester. (a1) Influence of catalyst concentration (1%, 5% and 10% of Zn2+) over Arrhenius plot, showing an accelerating effect with the increasing concentration. (a2) Modification of the Arrhenius plot and resulting activation energy with the use of different external catalysts (TBD, Zn(OAc)2 and P(Ph)3). Adapted with permission from ref. 23. Copyright 2012 American Chemical Society. (a3) Characteristic relaxation time as a function of the inverse temperature for several Brønsted acids having different pKa values. (a4) Linear relation between activation energy (Ea) and respective Brønsted acidity. Adapted with permission from ref. 24. Copyright 2018 American Chemical Society. (b) Exchange mechanism of the transamination of vinylogous urethanes. (b1) Arrhenius plot of several vinylogous urethane vitrimers loaded with different external catalysts (H2SO4, pTsOH, DBTL, TBD). Adapted from ref. 25 with permission from Springer Nature. (c) Exchange mechanism of the trans-N-alkylation of 1,2,3-triazolium salts. (c1) Characteristic relaxation time of poly(ionic liquids) made of different cross-linkers and alkylating agents (Br, I and mesyl-based). Reconstructed with permission from ref. 26. Copyright 2015 American Chemical Society. Notice to reader: further permissions related to the material excerpted of DOI: 10.1021/jacs.5b02653 should be directed to the ACS.
