RAFT-Mediated ab Initio Emulsion Copolymerization of 1,3-Butadiene with Acrylonitrile

The successful RAFT-mediated ab initio emulsion copolymerization of acrylonitrile and 1,3-butadiene using 2-(((dodecylsulfanyl)carbonothioyl)sulfanyl)propanoic acid (DoPAT) is reported at 45-55 degrees C. The number-average molecular weight exhibits a linear evolution as a function of monomer conversion (5000 <= M-n (g mol(-1)) <= 41000, 1.3 <= D (-) <= 3.3). Relatively good control (e.g., D approximate to 1.2 for selected conditions) over the polymerization up to moderate monomer conversion (50-60%) was attained when the employed initial molar ratio of RAFT agent to initiator was 2.5 or higher. Good omega-end-group functionality is evidenced by chain extension of NBR with a polystyrene block, with both H-1 NMR and SEC showing the average fraction of the NBR block as ca. 75 mol%. A kinetic model implemented via the PREDICI software package confirms the experimental findings, including a semiempirical approach to account for branch formation. The onset of the loss in control over the copolymerization at conversions >40% was tentatively attributed to branch formation. The current study evidences that RAFT mediated ab initio emulsion polymerization of 1,3-butadiene and acrylonitrile is a viable polymerization protocol for the synthesis of well-defined next generation nitrile-butadiene rubbers including in industrial context.