The effects of addition of different monomers on the molecular properties of poly(vinyl chloride) (PVC) have been studied. Three different additive monomers from N-phenyl maleimide derivatives were added with the same concentration 0.02 gm/1 gm PVC as stabilizers to PVC. These stabilizers are N-phenyl maleimide, Para-carboxy N-phenyl maleimide, and Para-amide carboxy N-phenyl maleimide (PA-NPMI). Their stabilizing efficiencies were evaluated by measuring the intrinsic viscosity of the solution samples. The results reveal that the type of the additive monomer plays a major role in determining the stabilizing potency of these materials. It was found that the PA-NPMI is the most effective stabilizer that improves the intrinsic viscosity of pure PVC from 1.02 to 1.19. So, the effect of its addition with different concentrations was studied. The results indicate that the sample with 0.015 gm PA-NPMI/1 gm PVC has higher intrinsic viscosity. Thus, this sample was chosen to be a subject for further study to investigate the effect of gamma irradiation on its molecular and color properties. Samples from the 0.015 gm PA-NPMI/1 gm PVC were irradiated with gamma doses in the range 5-100 kGy. It is found that the irradiation in the dose range 20-60 kGy enhances the intrinsic viscosity of the samples. In addition, the transmission of these irradiated samples in the wavelength range 200-2500 nm, as well as any color changes, was studied. The color intensity Delta E was greatly increased with increasing the gamma dose, and was accompanied by darkness with a significant increase in the yellow color component. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3060-3065, 2010