Fluorescence studies of the kinetics of processes in polyelectrolyte and ionomer solutions

Abstract

Abstract(1) A stopped‐flow apparatus with fluorescence detection was employed to follow the expansion of poly(methacrylic acid) (PMA) after a pH‐jump using either a dansyl‐labeled polymer (where emission is quenched by contact of the label with water) or doubly labeled PMA, where the efficiency of nonradiative energy transfer from the donor to the acceptor label decreases with chain expansion. The final approach to conformational equilibrium was found to be unexpectedly slow. (2) The kinetics of the enhancement of the fluorescence of Auramine 0 when it was mixed with the contracted form of PMA was insensitive to the polymer concentration, suggesting that it is due to a conformational transition of the polymer following the adsorption of the dye. (3) Partially ionized polycarboxylic chains carrying a β‐naphthol moiety were used to study the proton transfer from the excited naphthol to ionized carboxyls. The data suggested that the local chain flexibility is independent of the degree of ionization. (4) Solutions of slightly sulfonated polystyrene neutralized with aminomethyl naphthalene and aminomethyl anthracene, respectively, were mixed in the stopped‐flow apparatus and the kinetics of counterion interchange was deduced from the increasing efficiency of nonradiative energy transfer from the naphthalene to the anthracene label. (5) On mixing solutions of methyl methacrylate copolymers with small fractions of 4‐aminostyrene hydrochloride and N,N‐dimethylaminoethyl methacrylate, respectively, the HCl transfer from the aromatic to the aliphatic amine was followed by the increase of fluorescence. Using this model system, it was shown that the rate constant decreases with the length of the chains to which the interacting moieties are attached.