PURPOSE: To improve transparency and to lessen yellowness without lowering optical, chemical and physical characteristics of a formed article, by bringing pellets of a polymer into contact with inactive gas prior to processing them into a final product.

CONSTITUTION: Pellets of poly (glutarimide) are prepared in a heated extruder and they are turned into a viscoelastic molten material, conveyed to a mold or a die by a screw of the extruder and cooled in the mold or extruded from the die to be made a solid article. Prior to preparing the pellets in the extruder herein, they are brought into close contact with inactive gas for a time sufficient for removing completely the whole of oxygen in the pellets so that they may be inactivated completely. By this method, coloring with yellow which occurs in a processing stage antecedent to a forming or extruding operation can be lessened.