An analytical expression for the free energy of solutions of associative polymers is obtained in the entire polymer concentration-temperature range. This expression is derived under assumption that both local intrachain loops as well as interchain associations contribute to combinatorial part of the system free energy. In a good solvent regime, theory takes into account the swelling of polymer chains and suppression of pairwise associations due to strong monomer-monomer repulsive interactions. Analysis of the general expression of the system free energy shows that associations between functional groups can lead to a collapse of a chain and phase separation even under good solvent conditions for polymer backbone. In a good solvent, changing the fraction of associative groups per chain can trigger a phase separation.