her polyurethane polymers including polyester based polyurethanes are disclosed in the following patents: U.S. Pat. No. 2,871,218 disclosing extruded plastic sheets resistant to hydrocarbon solvents but soluble in polar solvents; U.S. Pat. No. 4,400,498 pertaining to heat and solvent resistant crosslinked polyurethanes particularly adapted to disperse fillers and pigments and useful for adhesives;