Evaluating the effect of termination by chain-chain coupling in living free-radical polymerizations

A novel approach based on the reaction of multifunctional star polymers with chromophore-labelled linear polymers is presented for evaluating the extent of termination by chain - chain coupling during living free-radical polymerizations. A mixed initiating system consisting of an unlabelled, multifunctional initiator and an excess of a monofunctional alkoxyamine initiator containing a chromophore, such as pyrene, is used to initiate the living polymerization of vinyl monomers leading to a mixture of star and linear polymers. The occurrence of chain - chain coupling is readily identified and quantified by isolating the star polymer that is obtained and elucidating the level of incorporation of pyrene units by UV/vis spectroscopy. This allows the level of chain - chain coupling to be determined since the inclusion of pyrene into the star structure is a direct result of termination by radical coupling.