Functionalization of SBR copolymer by free radical addition of thiols

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