Aqueous RAFT Polymerization of Acrylonitrile

Controlled radical polymerization of acrylonitrile (AN) in concentrated aqueous solutions of sodium thiocyanate (NaSCN, 50 wt %) and zinc chloride (ZnCl₂, 60 wt %) is reported. Reversible addition-fragmentation chain transfer (RAFT) polymerization was successfully accomplished with 4-cyano-4-(phenylcarbonothioylthio)pentanoic acid (CPAD) as a chain transfer agent (CTA) and AIBN as a radical initiator at 65 °C. First-order linear kinetic plots were observed in aqueous NaSCN with molecular weights (MW) between 3000 and 60"00 and relatively narrow molecular weight distributions (M_w/M_n = 1.2-1.4). Chain extension of the synthesized PAN macroinitiator with AN in aqueous NaSCN showed a clear shift in MWs which indicated high retention of chain end functionality. Furthermore, RAFT polymerization of AN in aqueous ZnCl₂ (60 wt %) was conducted with CPAD and 2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) as radical initiator at 30 °C. This system also exhibited linear kinetics and produced PAN with M_n = 13"300 but slightly higher dispersity (M_w/M_n = 1.38).