The results of Monte Carlo simulations of 2D polymer solutions are presented. The simulations were performed under athermal conditions for long chains (up to 1024 beads) over a full range of polymer concentration 0, explicitly taking into account the solvent molecules. The results obtained for short chains (N <= 256) are in good agreement with previous simulations whereas for long chains microphase separation is observed below phi = 0.6. This phenomenon is attributed to strong excluded volume interactions in 2D systems. A sort of interpenetration of the coils is also observed.