Synthesis of PVC polymer bonded to heterocyclic units is the field of our research . A number of heterocyclic units including 1,3,4 oxadiazole , 1,3,4 thiadiazole,porphyrine,bipyridine have been bound with PVC , In this study we attempt to modify poly (vinyl chloride), PVC by introducing benzimidazole and benzothiazole in the backbone of the PVC chain through chlorine displacement reaction , and we hope that such modification may showes interesting changes in overall thermal stability and interesting changes in over all properties of PVC such us , photostability , optical property , dielectric properties relative to un modified PVC, according to these finding , it was planned to frame a macromolecules which combine these two heterocyclic units for their characterization and photostability toward uv light.