Design of a Tunable Self‐Oscillating Polymer with Ureido and Ru(bpy)₃ Moieties

Abstract

An upper critical solution temperature (UCST)-type self-oscillating polymer was designed that exhibited rhythmic soluble-insoluble changes induced by the Belousov-Zhabotinsky (BZ) reaction. The target polymers were prepared by conjugating Ru(bpy) 3 ,acatalyst for the BZ reaction, to ureidocontaining poly(allylamine-co-allylurea) (PAU)c opolymers. The Ru(bpy) 3 -conjugated PAUs exhibited aUCST-type phasetransition behavior,and the solubility of the polymer changed in response to the alternation in the valency of Ru(bpy) 3 .T he ureido content influences the temperature range of selfoscillation, and the oscillation occurred at higher temperatures than conventional LCST-type self-oscillating polymers.F urthermore,the self-oscillating behavior of the Ru-PAU could be regulated by addition of urea, which is aunique tuning strategy. We envision that novel self-oscillating polymers with widely tunable soluble-insoluble behaviors can be rationally designed based these UCST-type polymers.Stimuli-responsive polymer materials are of interest owing to their ability to change their physicochemical properties in response to external stimuli (temperature,p H, light, and specific chemicals). These polymers have applications as smart materials,i ncluding soft actuators,b iosensors,d rug delivery systems,a nd cell culture materials. [1][2][3][4][5][6][7] Our research group has developed another class of smart materials known as "self-oscillating" polymers that autonomously undergo periodic soluble-insoluble or swelling-deswelling changes driven by an oscillating chemical reaction referred to as the Belousov-Zhabotinsky (BZ) reaction. [8,9] We have demonstrated the utility of self-oscillating materials as autonomous biomimetic materials,such as autonomous transport tubes, [10] artificial cells and amoeba composed of block copolymers, [11,12] and autonomous functional surfaces composed of polymer brushes. [13,14] Theb asic chemical structure of the self-oscillating polymer is ar andom copolymer composed of N-isopropylacrylamide (NIPAAm) and tris(2,2'-bipyridine) [Ru(bpy) 3 ]a s ac atalyst for the BZ reaction. Poly(NIPAAm) is one of the most widely studied thermoresponsive polymers;i te xhibits aphase transition from the soluble state to the insoluble state at the lower critical solution temperature (LCST). The poly(NIPAAm-co-Ru(bpy) 3 )a lso shows LCST-type phasetransition behavior and the LCST shifts to the higher temperature upon oxidation of the copolymerized Ru(bpy) 3 moiety.T he BZ reaction spontaneously generates periodic redox changes in the catalyst, and periodic hydrationdehydration of the polymer chain is induced at ac onstant temperature.A utonomous smart materials have been developed by functionalizing the LCST-type thermoresponsive poly(NIPAAm-co-Ru(bpy) 3 ).Fewp olymers show ap hase transition behavior at the upper critical solution temperature (UCST) in aqueous media. To induce UCST-type behavior in aqueous solutions, polymer-polymer interactions must be stronger than polymer-solvent interactions at lower temperatures....

Autonomous Vesicle/Sheet Transformation of Cell-Sized Lipid Bilayers by Hetero-Grafted Copolymers

“…In particular, the hetero-grafted copolymer architecture allowed us to manipulate nano-interfaces at the lipid bilayer edge with nanometer thickness and micrometer span. Smart copolymers that exhibit coil–globule transitions in response to various external stimuli such as pH, light, redox changes, or specific chemicals have been prepared. − By integrating these polymer materials into the hetero-grafted copolymer architectures, we can engineer lipid membrane dynamics in response to the desired stimulus. To date, lipids in the form of vesicles and not sheets have been widely utilized in the diverse fields of life sciences and engineering, such as medicines and cosmetics.…”