Afterchlorinated vinyl chloride polymers

Claim 1

A process for the dry chlorination of powdery vinyl chloride polymers with gaseous chlorine comprising the steps: 1. introducing chlorine into a reaction vessel containing the vinyl chloride polymer powder and maintaining the polymer in a chlorine atmosphere in the absence of radical-forming initiators, radical-forming initiating radiation or both at temperatures of at most about 50° C. for at least 30 minutes; 2. raising the temperature of the reaction to a temperature of at least 70° C., but below the agglomeration temperature of the vinyl chloride polymer, such that thermal radical-formation occurs and chlorination of the vinyl chloride polymer occurs to the required chlorine content thereby producing chlorinated vinyl chloride polymer powder; the relationship between the time required for the two steps is such that the reaction time of the first step is selected to be such that, in the second step, in the temperature range at which thermal radical-formation occurs, no thermal degradation and subsequent product discoloration occurs thereby producing a chlorinated vinyl chloride polymer powder having a chlorine content in excess of the starting vinyl chloride polymer.