The synthesis of poly(vinyl chloride) (PVC) modified with p-aminothiophenol is described. The presence of free amino groups in the products is proven and their content measured by nuclear magnetic resonance and infrared spectroscopy, and elemental analysis. Modification degrees of up to 30% can be achieved without degradation or other side-reactions. The amino group containing polymers can be easily cross-linked or modified, yielding gels, networks or PVC with covalently bound plasticizers.