Sol–gel reversible metallo-supramolecular hydrogels based on a thermoresponsive double hydrophilic block copolymer
A well-defined poly(N,N-dimethylacrylamide)-b-poly(N-isopropylacrylamide-co-2-vinyl-4,4-dimethylazlactone) thermoresponsive double hydrophilic block copolymer bearing a terpyridine entity (Tpy-PDMA-b-P(NIPAM-co-VDM)) was synthesized by successive RAFT polymerizations. An amphiphilic macro-chain transfer agent bearing a terpyridine moiety (Tpy-PDMA-CTA) was synthesized and used for the preparation of a double hydrophilic block copolymer (Tpy-PDMA-b-P(NIPAM-co-VDM)) by RAFT dispersion polymerization. The RAFT dispersion polymerization of water-soluble monomers showed good control over the molar mass and dispersity, as characterized by size exclusion chromatography (SEC) and 1H-NMR spectroscopy. Complexation in the presence of metal ions (Fe2+) and self-assembly of the Tpy-PDMA-b-P(NIPAM-co-VDM) copolymer in diluted solution (0.5% w/v) were investigated. The formation of dynamic metallo-supramolecular flower-like micelles was demonstrated by UV-Vis spectrophotometry and dynamic light scattering (DLS). The effect of the addition of Fe2+ ions to a concentrated solution (8% w/v) of the Tpy-PDMA-b-P(NIPAM-co-VDM) copolymer at low temperature was investigated and the thermal profile of the metallic bis-terpyridine complex ([Fe(Tpy-PDMA-b-P(NIPAM-co-VDM))2]2+) has been studied by differential scanning calorimetry (DSC). The influence of temperature on the aqueous solution (8% w/v) of the ([Fe(Tpy-PDMA-b-P(NIPAM-co-VDM))2]2+) metallic complex was investigated by rotational rheometry. The results show that the self-assembly of the thermoresponsive block of the metallic bis-terpyridine complex formed a dynamic hydrogel with a sol–gel thermoreversible transition.