Polymer composition containing oxidation-modifiable chlorinated propylene and method for producing same

Provided is a production method with which, by virtue of having a step for chlorinating an oxidation-modifiable propylene-containing polymer using a mixed solvent of chloroform and water, it is possible to produce more efficiently than in the past a polymer composition containing oxidation-modifiable chlorinated propylene that shows little discoloration, contains no polarizing component impurities or low-molecular-weight components, has excellent compatibility with polyurethane resins, and shows excellent adhesion of ink binders containing polyurethane when used for a variety of materials (particularly OPP). At least one polymer containing oxidation-modifiable propylene selected from oxidation-modifiable polypropylene and oxidation-modifiable propylene-alpha-olefin copolymer is dispersed in a mixture containing chloroform and water and chlorinated at a temperature of 130 C or lower to obtain a polymer composition containing oxidation-modifiable chlorinated propylene.