Molecular Design of Novel Self-Oscillating Polymer Chains Fuelled by Organic Acid Under Constant Condition

Abstract

Stimuli-responsive polymers system, which responds to external stimuli such as temperature, pH, electric fields, etc., have been much investigated in order to apply to actuators, artificial muscle, drug delivery systems (DDS), shape-memory, molecular recognition material, separation-system and purification material, etc. [1-21] However, the conventional-type stimuli-responsive polymer system provides only one unique action to the external stimulus. On the other hand, many biological systems, such as the brain waves, autonomic heartbeat and periodic hormone secretion, show autonomous oscillations and respond to external stimuli. If we construct the autonomous polymer system like a living organism with tailor-made design, unprecedented polymer system would be realized. In this study, in order to construct the autonomous polymer system like a living organism, the Belousov-Zhabotinsky (BZ) has been utilized as the chemical energy source of the autonomous motion for polymer systems. The BZ reaction is well known as an oscillating reaction accompanying spontaneous redox oscillations to generate a wide variety of nonlinear phenomena, e.g., target or spiral pattern in an unstirred solution, and periodicity, multi-periodicity, or chaos in a stirred solution [2230]. The overall process of the BZ reaction is the oxidization of an organic substrate by an oxidizing agent in the presence of the catalyst under strong acidic conditions. In the BZ reaction, the metal catalyst undergoes spontaneous redox oscillation. In the case of utilizing the ruthenium tris(2,2’-bipyridine) that is the metal catalyst of the BZ reaction, the Ru catalyst has the different solubility in the reduced and oxidized states, respectively: the reduced Ru catalyst has a hydrophobic property, and the oxidized one has a hydrophilic one. In order to cause the self-oscillation of the polymer system (liner-polymer chain and polymer gel), polymer main-chain covalently bonded to the (ruthenium (4-vinyl-4’-methyl2,2-bipyridine) bis(2,2’-bipyridine)bis(hexafluorophosphate)) (Ru(bpy)3) as a catalyst of the BZ reaction were synthesized [31-33]. The main-chain of the self-oscillating polymer system adopted thermoresponsive poly(Nisopropylacrylamide) (poly(NIPAAm)). As a result, the polymer system cause the autonomous and spontaneous aggregation-disaggregation selfoscillation for the linear-polymer chain and the swelling-deswelling self-oscillation for the polymer gel under the constant temperature conditions with the coexistence of the BZ substrates other than the metal catalyst. However, operating condition of the self-oscillating