Mechanistic Insights into Temperature-Dependent Trithiocarbonate Chain-End Degradation during the RAFT Polymerization of N-Arylmethacrylamides

Mechanistic insights into trithiocarbonate degradation during the RAFT polymerization of N-arylmethacrylamides are reported. Previous work by our group showed significant RAFT agent degradation during the polymerization of N-arylmethacryloyl sulfonamides at 70 °C. Herein we report the influence of methacrylamide structure on trithiocarbonate degradation during the RAFT polymerizations of N-phenylmethacrylamide (PhMA) and N-benzylmethacrylamide (BnMA) in DMF at 70 and 30 °C. UV–vis spectroscopy revealed trithiocarbonate degradation occurs exclusively after covalent addition of monomer to the RAFT agent, with 60% trithiocarbonate degradation occurring after 12 h during the polymerization of PhMA at 70 °C compared to only 3% degradation measured during the polymerization of BnMA under identical conditions. Small molecule analogues of trithiocarbonate-functional poly(PhMA) and poly(BnMA) were synthesized by single monomer unit insertion and the kinetics and byproducts of degradation investigated by in situ 1H NMR analysis at 70 °C. Trithiocarbonate degradation was ultimately shown to occur by N-phenyl-promoted, N-5 nucleophilic attack on the terminal thiocarbonyl by the ultimate methacrylamide unit.