Visible-light induced RAFT polymerization of styrenic monomers with aromatic aldehydes as organophotoredox catalysts

A photoinduced electron transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of p-methylstyrene (p-MS) and styrene (St) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid as the chain transfer agent (CTA) and aromatic aldehydes, including 4-cyanobenzaldehyde (PC1), 2,4-dimethoxy benzaldehyde, and 4-methoxy benzaldehyde, as organic photocatalysts has been demonstrated via irradiation with 23 W compact fluorescent lamps. The kinetics of the polymerizations shows first order with respect to monomer conversions. Linear evolution of the M-n of the produced polymers with the monomer conversion is observed. Meanwhile, the as-prepared polymers are of relatively narrow polydispersity (PDI=M-w/M-n). For instance, the polymerization of p-MS shows living polymerization features using PC1 within a range of solvents. Especially, the M-n of PpMS increased from about 2100 to 12,700 g/mol with the monomer conversion from 8% to 52% in tetrahydrofuran. The controlled polymerization of St is also observed under optimal reaction conditions. However, the M-n discrepancy between the experimental readings and theoretical calculations is greater at the monomer conversions greater than 40% and the PDI increased gradually over the monomer conversion. This is probably because that CTA is strongly sensitive to the light irradiation with wave range around its characteristic absorption wavelength, leading to significant decomposition of CTA moieties during the RAFT polymerization. (C) 2018 Wiley Periodicals, Inc.