Dimension Changes in a Chemomechanical Polymer Containing Ethylenediamine and Alkyl Functions as Selective Recognition Units

Abstract

AbstractTreatment of polymethyl methacrylate with dodecylamine and diethylenetriamine produces a chemomechanical polymer, which undergoes large macroscopic motions as a result of selective recognition of substrates (effectors) in the surrounding aqueous solution. The kinetics of these fully reversible expansions and contractions are compared to those of effector absorption and desorption. The expansion correlates with a polymer particle weight increase, which is in turn found to be largely a function of the uptake of water necessary for solvation of the effector molecules. The selectivity of the motions depends on the nature and placement of the effector ionic sites, and also on the size and nature of the organic residues. Ion pairing between the protonated amine functions and inorganic anions or anionic groups of organic effectors plays a decisive role. The large effects seen with aromatic effectors such as nucleotides, in contrast with saturated analogues, point to cation–π and C–H–π interactions as essential elements for the distinction between different effectors, including isomeric compounds. The material exhibits symmetric expansion/pH profiles, which depend distinctly on the ionic strength of the solution. The strong dependence of the motions not only on the applied pH, but also on the concentrations of two simultaneously active effectors, such as AMP and phosphate, present chemically induced logical gate functions; this is tentatively explained by a two‐site binding model. In contrast, the large expansions produced by simultaneous action of, for example, copper or zinc and amino acids or peptides are due to co‐complexation between the metal ions and known organic chelators. With such ternary complexes, volume expansions by factors of up to 15 are possible with effector concentrations as low as 0.25 mM. The sensitivity can be further increased by miniaturization of the polymer particles; the velocity of the response can be optimized by increasing the surface‐to‐volume ratio. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)