KINETICS AND MECHANISM OF INTERPOLYELECTROLYTE EXCHANGE AND ADDITION-REACTIONS

Transfer of relatively short polycation chains (guest polyelectrolyte, GPE) from their polyelectrolyte complex (PEC) with a relatively long polyanion (host polyelectrolyte, HPE) to another polyanion of the same chemical structure and chain length but tagged with a fluorescent group has been investigated by the luminescence quenching technique. It has been shown that if only one polycation chain, on average, is transferred, the reaction follows irreversible second-order kinetics. The irreversibility of the reaction is due to additional selective nonelectrostatic interaction between the polycations and polyanion chains, carrying pyrenyl groups. The rate constant of the exchange reaction is independent of polyanion chain length and increases sharply with an increase of ionic strength of water-salt solution, a decrease of polycation chain length, and a decrease of the charge density. In accordance with the proposed mechanism, the rate-limiting step of the reaction is the transfer of a polycation chain from one polyanion to the other one in the united coil HPE-GPE-HPE*. The polyion addition reaction, i.e. the complexation between two oppositely charged polyanions, also has been studied by luminescence quenching and quasielastic light scattering techniques. The reaction can be considered as a multistage process, consisting first of the rapid coupling of the oppositely charged polyions with the formation of a nonequilibrium interpolyelectrolyte network followed by the slow relaxation process, leading finally to the formation of the individual PEC.