A systematic study on Zn(II)-Iminocarboxyl complexation applied in supramolecular PDMS networks

Metal-ligand coordination was used to construct supramolecular elastomers with self-healing ability and excellent mechanical properties. In this study, novel iminocarboxyl-functionalized polysiloxanes (PDMS-Iminocarboxyl) was synthesized through amine-functionalized polysiloxanes (PDMS-NH2) with acrylic acid by aza-Michael addiction based on 1H NMR and FTIR spectroscopy. The incorporation of zinc ions into the PDMS-Iminocarboxyl as chemical crosslinks could essentially improve the thermal and mechanical properties because of highly dynamic Zn(II)-iminocarboxyl complexation. The stoichiometric ratio of [Zn2+]/[COOH] were determined by NMR titration. Furthermore, the presence of dynamic Zn(II)-iminocarboxyl equilibrium could allow a degree of strain sensitivity upon various stretching rates based on tensile experiments and rheological analysis. From the DMA and rheological analysis, modulus transition of PDMS-Iminocarboxyl@Znx networks was closely related to the association-dissociation of Zn(II)-iminocarboxyl complexation. Besides, DFT calculations further provided the optimized configuration of metal-ligand complex according to the bond-valence-bond-length correlations.