Unique thermo-induced sequential gel - Sol - gel transition of responsive multiblock copolymer-based hydrogels

The relative dominance of hydrophobic and electrostatic supramolecular interactions in aqueous solutions of responsive multiblock copolymers was thermoregulated. pH responsive poly(4-vinylpyridine) (P4VP) and thermosensitive random copolymer of N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide (DMA), P(NIPAM-co-DMA), were chosen as the two chain sequences alternately arranged in m-P-(NIPAM-co-DMA)-b-P4VP multiblock copolymers. A comparison to the aggregation properties of the multiblock in dilute aqueous solution shows that at 5°C, ionic complexation between protonated P4VP and NDSNa is responsible for the physical gelation, which leads to insolubility of P4VP sequences. Cooling from the gel state at 55°C to 5°C realize sequential gel-sol-gel transition in the reverse order, as compared to that observed in the heating process.