How is the CO2 contaminating the polymer? is it occluded in the polymer matrix?
If you are using LCO2 or SCO2 (as zsinger suggests) as a solvent then it is usually best to use an aprotic polar solvent and vacuum to pull the residue CO2 out of solution.
If you are occluding CO2 during processing though, any solvent is going to be harder to remove than a substance which is naturally a gas at STP.