AbstractThe effect of gamma ray irradiation on chlorendic acid based unsaturated polyesters was studied. Four different types of unsaturated polyesters, made by varying the molar ratios of chlorendic acid to isophthalie acid were irradiated with a Co60 qource. After irradiation, the chlorine content decreases rapidly as the isophthalate content in the polyester chain increases. As the chlorendle acid content increases, the change in acid value after irradiation decreases. The increase in intrinsic viscosity is quite marked in high isophthalate containing polyesters after gamma ray irradiation and there is a noticeable decrease in intrinsic viscosity after gamma irradiation of high chlorendic acid containing polyesters. The effect of gamma irradiation on the percentage of cis and trans forms of these polyesters was studied with the help of infrared spectra. It appears that as the chlorendic acid content increases, on gamma irradiation conversion from trans unsaturation to cis unsaturation increases rapidly.