(Original) A process for chlorinating a polymer in an aqueous medium, said process comprising the following steps: a. charging a closed vessel with polymer powder and water to obtain a suspension; b. introducing chlorine gas into said closed vessel containing said suspension till a pressure in the range of 0.5 to 2 bar is attained to obtain a reaction mixture; c. stirring said reaction mixture to obtain a slurry; d. dissociating the chlorine molecules into chlorine radicals in two stages: • dissociating a first portion of the chlorine molecules by irradiating said slurry with radiation having an intensity in the range of 3 watt/Kg to 10 watt /Kg and wavelength in the range of 250 to 550 nm at a temperature less than the softening temperature of said polymer; and • further dissociating a second portion of the chlorine molecules, by gradually increasing the temperature of said slurry from less than the softening temperature of said polymer to a temperature above the softening temperature of said polymer thereby thermally dissociating the chlorine molecules, into chlorine radicals, while gradually reducing the intensity of the radiation to zero; wherein, the steps of gradually increasing the temperature and gradually reducing the intensity of radiation are carried out over a time period in the range of 1 hour to 8 hours; e. allowing said dissociated chlorine radicals to react with said polymer to obtain a mixture comprising the chlorinated polymer; and f. recovering said chlorinated polymer, wherein said process is carried out in the absence of a swelling agent, a dispersing agent and an initiator. a. charging a closed vessel with polymer powder and water to obtain a suspension; b. introducing chlorine gas into said closed vessel containing said suspension till a pressure in the range of 0.5 to 2 bar is attained to obtain a reaction mixture; c. stirring said reaction mixture to obtain a slurry; d. dissociating the chlorine molecules into chlorine radicals in two stages: • dissociating a first portion of the chlorine molecules by irradiating said slurry with radiation having an intensity in the range of 3 watt/Kg to 10 watt /Kg and wavelength in the range of 250 to 550 nm at a temperature less than the softening temperature of said polymer; and • further dissociating a second portion of the chlorine molecules, by gradually increasing the temperature of said slurry from less than the softening temperature of said polymer to a temperature above the softening temperature of said polymer thereby thermally dissociating the chlorine molecules, into chlorine radicals, while gradually reducing the intensity of the radiation to zero; wherein, the steps of gradually increasing the temperature and gradually reducing the intensity of radiation are carried out over a time period in the range of 1 hour to 8 hours; • dissociating a first portion of the chlorine molecules by irradiating said slurry with radiation having an intensity in the range of 3 watt/Kg to 10 watt /Kg and wavelength in the range of 250 to 550 nm at a temperature less than the softening temperature of said polymer; and • further dissociating a second portion of the chlorine molecules, by gradually increasing the temperature of said slurry from less than the softening temperature of said polymer to a temperature above the softening temperature of said polymer thereby thermally dissociating the chlorine molecules, into chlorine radicals, while gradually reducing the intensity of the radiation to zero; wherein, the steps of gradually increasing the temperature and gradually reducing the intensity of radiation are carried out over a time period in the range of 1 hour to 8 hours; e. allowing said dissociated chlorine radicals to react with said polymer to obtain a mixture comprising the chlorinated polymer; and f. recovering said chlorinated polymer,