Fig. 2. Examples of “neighbouring group participation (NGP) effect” in vitrimers enabling a fine tuning of exchange reactions and thus viscoelastic properties. Neighbouring groups are displayed in green and exchanging moieties in blue. (a) Citric acid-based esters with unreacted free carboxyl acid in close proximity to ester bonds.32 (b) Boronic ester exchanges and amino-NGP influence.34 (c) Silyl ether exchanges and amino-NGP influence.35 (d) Phthalate monoesters with free carboxyl or sulfonic acid groups in close proximity.36,37.
