The present disclosure provides an effective and efficient process for the preparation of a dry chlorinated polyvinyl chloride (CPVC), comprising introducing chlorine gas into slurry of polyvinyl chloride in water to obtain a reaction mixture; irradiating the reaction mixture to obtain a product mixture comprising CPVC and water solution including unreacted chlorine gas and hydrogen chloride; filtering the product mixture to obtain a first mass; adding water to the first mass for extracting unreacted chlorine gas and hydrogen chloride to obtain an aqueous suspension, and filtering the aqueous suspension to obtain a second mass; passing nitrogen through the second mass to extract residual water solution to leave behind a third mass; and agitating the third mass in a high-speed mixer together with a neutralizing agent, and optionally with a stabilizer and a processing additive to obtain dry thermally stable CPVC with thermal stability in the range of 1000 seconds to 1500 seconds.