The interpolymer association between acrylic acid (AA) copolymers and poly(ethylene glycol) (PEG) was investigated through viscometric and potentiometric measurements. The AA copolymers used contained carboxylate (COO-), sulfonate (SO3-), or isopropylamide (CONHCH(CH3)(2)) groups introduced by neutralization, copolymerization, or condensation reactions, respectively. The experiments were performed under a low and constant ionic strength, I congruent to 1.0 x 10(-3) M, and constant pH conditions, following the known isoionic dilution method. The poly(acrylic acid) association with PEG, due to interpolymer hydrogen bonding, results in the formation of compact aggregates. When the percentage molar degree of substitution (DS) in carboxylate or sulfonate groups is higher than 10%,the interpolymer association is prevented, while this still exists for DS = 30% in isopropylamide groups. The obtained results show a significant differentiation in the association between the AA copolymers containing charged groups, COO- or SO3-, and neutral groups, CONHCH(CH3)(2). The presence of these neutral groups in a first stage till DS = 10%, probably due to synergistic hydrophobic forces, favors the interpolymer association. This association is weakened later and finally prevented for DS > 30% because of a corresponding decrease of the hydrogen bonding, which is mainly responsible for this interpolymer association.