Thermo- and redox-responsive dendronized polymer hydrogels
In order to combine dendritic structures and thermoresponsiveness within the field of metallo-supramolecular chemistry, a novel type of smart hydrogel was prepared through ferrous ion-induced supramolecular interactions from oligoethylene glycol (OEG)-based, first-generation (G1) dendritic copolymers containing terpyridine (Tpy) moieties. These hydrogels show both thermally-induced reversible shrunk-swelling and redox-mediated gel–sol transitions. Rheological analyses by rotational rheometry revealed that their storage modulus (G′) and loss modulus (G′′) were dependent on crosslinking density through changing the molar ratio of metal ions and Tpy moieties, as well as the copolymer composition with different ratios of OEG dendron and Tpy units. Copolymers pendanted with linear OEG units and second-generation (G2) dendrons were also prepared to compare the possible effects of architecture on the formation of hydrogels and their properties. By virtue of the thermoresponsiveness of these dendronized copolymers, hydrogels were further prepared through crosslinking of aggregates above the polymer phase-transition temperatures, which provides a convenient strategy to afford hydrogels with much improved elastic modulus. Moreover, encapsulation and thermally-mediated transition of the model drug from the hydrogels were investigated, to demonstrate the unique confinement from the OEG-based dendronized polymer matrix. This report provides not only a first route to fabricate intelligent hydrogels from dendronized copolymers through metal ions-mediated coordination, but also proves that thermoresponsive hydrogels with enhanced mechanical properties could be simply prepared by crosslinking thermally-induced polymer aggregates.