The present disclosure relates to a process for the preparation of CPVC which includes reacting PVC with chlorine at a pre-determined temperature in the presence of at least one irradiation source having wavelength ranging from 254 and 530 nm while maintaining the radiant flux from 1.5 to 2 W/kg of PVC, irradiance at 0.13 W/cm2 and the number of photons emitted per second from 3×1018 to 5×1018, under agitation, for a time period ranging from 3 to 4 hours to obtain CPVC. The CPVC prepared from the afore-stated process has a whiteness index ranging from 89 to 96, a yellowness index ranging from 1.23 to 1.73 and stability ranging from 648 to 684 seconds. The rate of the chlorination reaction after employing the afore-stated process parameters ranges from 1.6 to 4.36 mole/hour/kg.