The results of Monte Carlo simulations of 2D polymer solutions are presented. The simulations were performedunder athermal conditions for long chains (up to 1024 beads) over a full range of polymer concentration φ, explicitlytaking into account the solvent molecules. The results obtained for short chains (N ≤ 256) are in good agreementwith previous simulations whereas for long chains microphase separation is observed below φ = 0.6. This phenomenonis attributed to strong excluded volume interactions in 2D systems. A sort of interpenetration of the coils is alsoobserved.