The functionalization of a styrene/butadiene (20/80) random copolymer (SBR) is performed by radical-mediated addition Of L-cysteine derivatives to the macromolecules' double bonds. The reaction carried out in solution and in the melt leads to SBR chain bearing amino and carboxylate functionalities through thiol addition to the vinyl double bonds of the 1,2-butadiene units with anti-Markovnikov regioselectivity. The addition yield (up to 5 wt%) and the occurrence of the crosslinking side reaction are investigated with reference to feed conditions and process parameters. The optical rotation of the reaction products confirms the addition Of L-Cysteine to SBR chain and provides a simple route to prepare optically-active polymers containing pendant amino acid residues. (c) 2006 Elsevier Ltd. All rights reserved.