Dithiobenzoate-Mediated Reversible Addition-Fragmentation Chain Transfer Polymerization of Methyl Methacrylate in O2-Rarefied and Hydroxyl-Labile Dimethyl Sulfoxide

The effect of H 2 O 2 and H 2 O 2 -ascorbic acid (Vc) pairs on defunctionalization of 2-cyano-2-propyl dithiobenzoate (CPDB) and CPDB-mediated reversible addition-fragmentation chain transfer (RAFT) polymerization of methyl methacrylate (MMA) in dimethyl sulfoxide (DMSO) is investigated. The stability of CPDB toward H 2 O 2 is monitored by UV–vis absorption spectroscopy. CPDB is partially defunctionalized by H 2 O 2 alone and more seriously by H 2 O 2 -Vc pairs at 40°C, due to the oxidation by H 2 O 2 and the stepwise addition of DMSO-derived H 3 C· radicals. MMA greatly inhibits the defunctionalization of dithiobenzoate moieties, as both HO· and H 3 C· radicals incur oligomeric MMA-terminated alkyl radicals, which conserve the dithiobenzoate moieties of CPDB. H 2 O 2 -Vc-initiated CPDB-mediated RAFT polymerization is undertaken at 30°C and 40°C. Conversion is measured by gas chromatography, and molecular weight (MW) of PMMA is determined by gel-permeation chromatography. The processes manifest a moderately controlled fashion under optimal conditions. The products at low conversion display a multi-component composition, with high-MW PMMA consisting of 90% at least. MW of PMMA increases almost linearly with the yield and maintains a narrow distribution, but higher than the corresponding theoretical MW, owing to the partial defunctionalization of CPDB. Mass spectroscopy reveals that the irreversible termination of the intermediate radicals is the primary factor. Graphical H 2 O 2 initiated reversible addition-fragmentation chain transfer (RAFT) polymerization in dimethyl sulfoxide (DMSO) with 2-cyano-2-propyl dithiobenzoate (CPDB) as both the reducing agent and CTA. The defunctionalization of CPDB by H 2 O 2 in DMSO was observed, but methyl methacrylate significantly inhibited the defunctionalization. The CPDB-mediated RAFT polymerization was fulfilled with H 2 O 2 or H 2 O 2 -Vc pairs as the initiator. MS attributed the defunctionalization to the formation and the irreversible termination of lower-activity intermediate radicals.