Self-oscillating AB diblock copolymer developed by post modification strategy

We prepared AB diblock copolymer composed of hydrophilic poly(ethylene oxide) segment and self-oscillating polymer segment. In the latter segment, ruthenium tris(2,2′-bipyridine) (Ru(bpy)₃), a catalyst of the Belousov-Zhabotinsky reaction, is introduced into the polymer architecture based on N-isopropylacrylamide (NIPAAm). The Ru(bpy)₃ was introduced into the polymer segment by two methods; (i) direct random copolymerization (DP) of NIPAAm and Ru(bpy)₃ vinyl monomer and (ii) post modification (PM) of Ru(bpy)₃ with random copolymer of NIPAAm and N-3-aminopropylmethacrylamide. For both the diblock copolymers, a bistable temperature region (the temperature range; ΔT_m), where the block copolymer self-assembles into micelle at reduced Ru(bpy)₃²⁺ state whereas it breaks-up into individual polymer chain at oxidized Ru(bpy)₃³⁺ state, monotonically extends as the composition of the Ru(bpy)₃ increases. The ΔT_m of the block copolymer prepared by PM is larger than that by DP. The difference in ΔT_m is rationalized from the statistical analysis of the arrangement of the Ru(bpy)₃ moiety along the self-oscillating segments. By using the PM method, the well-defined AB diblock copolymer having ΔT_m (ca. 25 °C) large enough to cause stable self-oscillation can be prepared. The periodic structural transition of the diblock copolymer in a dilute solution ([Polymer] = 0.1 wt. %) is closely investigated in terms of the time-resolved dynamic light scattering technique at constant temperature in the bistable region. A macroscopic viscosity oscillation of a concentrated polymer solution (15 wt. %) coupled with the periodic microphase separation is also demonstrated