Self-association in aqueous solution of amphiphilic poly(acrylic acid)-b-poly(propylene oxide)-b-poly(acrylic acid) (PAA-b-PPO-b-PAA) copolymers having various outer PAA block lengths are presented. These copolymers show two thermosensitive behaviors. The first one, due to hydrogen bonds between PAA and PPO resulting in large aggregates, was observed by visible spectroscopy. The second one, due to the association of PPO middle block into aggregates, was evidenced by dynamic light scattering and pyrene fluorescence. These critical temperatures both depend on the ionization and the length of PAA blocks. The characterization of the aggregates above the critical aggregation concentration by fluorescence quenching experiments showed a very low aggregation number corresponding to dimers or trimers association depending on the conditions. (C) 2016 Wiley Periodicals, Inc.