Functionalization of SBR copolymer by free radical addition of thiols

The reaction of the random styrene/butadiene copolymer (SBR) with two functional thiols (thioglycolic acid and its aliphatic ester) in the presence of free radical initiators is described. The reaction leads to addition of the thiol group to the vinyl double bonds of the 1,2-butadiene units of the copolymer with high selectivity. As a consequence the resulting macromolecules contain covalently bonded carboxylic or carboxylate groups. The influence of the reaction conditions on the relative probability of the addition reaction with respect to crosslinking, degradation and chain transfer reactions is discussed. The degree of functionalization (FD) can be modulated in the range from 1 to 10 mol-%.