The scope for synthesis of macro-RAFT agents by sequential insertion of single monomer units

The scope for synthesis of new macro-RAFT agents (Z–C(S)S–(M)–R) by sequential insertion of monomers (M) 'one at a time' into an initial RAFT agent (Z–C(S)S–R) has been explored. The process is illustrated with the preparation of a styrene-N-isopropylacrylamide (NIPAM) co-dimer macro-RAFT agent [(CH3)3C(CN)–CH2CH(Ph)–CH2CH(CONHiPr)–SC(S)–S-alkyl] by successive single unit monomer insertions into a cyanoisopropyl trithiocarbonate. Critical factors for success are a high transfer constant for the RAFT agent and a high rate of addition of the radical (R·) to monomer relative to further propagation. With these conditions satisfied, the rate of reaction is largely determined by the rate of R· adding to monomer. Initiator-derived by-products (Z–C(S)S–(M)–I) become an issue when R· is different from the initiator-derived radical (I·).