Abstract: Olefin polymer chlorination products having improved handling properties are prepared by reacting, in a fluidized-bed state, certain free-flowing, high bulk density linear olefin polymer powders with gaseous chlorine. The olefin polymer powder used is characterized by having a flowability measured as angle of repose in the range of from about 24.degree. to about 28.degree., a bulk density in the range of from about 25 to about 35 pounds/cubic foot and a surface area in the range of from about 2 to about 4 square meters/gram. The individual particles of the olefin polymer particle are characterized by having particle sizes predominantly in the range of from about 300 to about 600 microns, and porosity sufficient to provide an average free volume within individual particles in the range of from about 20 to about 45 volume percent based on total particle volume.