pH-responsive micellization of amine-containing cationic diblock copolymers prepared by reversible addition-fragmentation chain transfer (RAFT) radical polymerization

Abstract

A series of poly([3-(methacryloylamino)propyl]trimethylammonium chloride)-block-poly(2-(diethylamino)ethyl methacrylate) (pMAPTAC m-DEAEMAn) of different block lengths were prepared by controlled radical polymerization based on reversible addition-fragmentation chain transfer (RAFT). The diblock copolymers have a narrow distribution in their molecular weights, the ratios of weight- and number-average molecular weights (Mw/Mn) being in the range of 1.04-1.05. On the basis of 1H NMR, quasielastic light scattering (QELS), static light scattering (SLS), and fluorescence probe data, these diblock copolymers exhibited reversible micelle formation and dissociation in aqueous solutions induced by a pH change. The hydrodynamic radius (Rh) and apparent molecular mass for the diblock copolymer increased abruptly near pH 7 with increasing pH, indicative of the micelle formation at basic pHs. Fluorescence spectra for N-phenyl-1-naphthylamine (PNA) probes suggested that hydrophobic molecules such as PNA were incorporated into hydrophobic cores in the micelle. PNA probes were released into the bulk water phase when the micelle was dissociated at pH ≤ 7. The capture of the fluorescence probe at pH > 7 and its release at pH ≤ 7 occur reversibly as a result of the formation and dissociation of the micelle upon pH change.