Ultra-precise insertion of functional monomers in chain-growth polymerizations

Chain-growth polymerizations are popular methods because they allow synthesis of high-molecular weight polymers in high yields and in short times. However, copolymers prepared by such processes generally exhibit uncontrolled monomer sequences. The controlled radical copolymerization of styrene with N-substituted maleimides is an interesting exception allowing preparation of controlled primary structures. However, because of the statistical nature of chain-growth mechanisms, sequence deviations are still present in these copolymers. Here we describe a specific range of experimental conditions that allows ultra-precise incorporation of a single N-substituted maleimide unit in a polystyrene chain. This occurs in a given kinetic regime where the styrene/N-substituted maleimide comonomer ratio is very low. This situation usually only arises in the later stages of a chain-growth polymerization. Nevertheless, we show that it is possible to restore these particular kinetic conditions multiple times during a single polymerization by using successive feeds of donor and acceptor comonomers. Copolymers prepared by controlled radical chain-growth polymerizations usually contain ill-defined monomer sequences. Here, successive feeds of donor and acceptor comonomers are used to control the primary structure of the synthesized copolymers with very high accuracy.