Reactions of polystyrene radicals in a monomer-free atom transfer radical polymerization system

Polystyrene radicals (PS•) were produced in high concentration using ω-bromopolystyrene (PS-Br) and α,ω-dibromopolystyrene (Br-PS-Br) in conjunction with Cu(I)Br following the atom transfer technique. A proper choice of the activator system led the PS-Br adduct to a maximum extent of coupling (by recombination), q_max = 0.91, as estimated by gel permeation chromatography. On the other hand, the fraction of chains terminated by disproportionation was estimated to be 0.07 ± 0.04 by ¹H NMR. When the radical concentration [PS•] was not high enough, the chain transfer reaction competed with termination, and q_max remained low. For the bifunctional adduct Br-PS-Br, the coupling reaction produced 'polymers' of a variety of chain lengths, whose distribution obeyed the theory of random coupling, when q was lower than about 0.5. The high extent of coupling (q_max ≈ 0.9) achievable in short time (< 10 min) suggests practical applicability of this reaction.