ABA-triblock copolymers are synthesized by a low-temperature acceptor polycondensation in a solution. Polyoxyethylene is B (molecular weight: 1000, 2000 and 4000), the block consisting of the para-hydroxybenzoic acid residues is A. The aggregation of block copolymers in water and in chloroform is investigated by dynamic light scattering, static light scattering and viscosimetry. Hydrodynamical radius of particles in solutions is calculated. Also values of inherent viscosity and Huggins constants are determined. Assumptions about association mechanisms are stated.