Toward Understanding of Branching in RAFT Copolymerization of Methyl Methacrylate through a Cleavable Dimethacrylate

We report the reversible addition–fragmentation chain transfer (RAFT) solution copolymerization of methyl methacrylate (MMA) with a cleavable divinyl comonomer, bis­(2-methacryloyl)­oxyethyl disulfide (BMAODS). 2-Cyano-2-propyl­dodecyl trithiocarbonate was used as a RAFT chain transfer agent and 2,2′-azobis­(2-methyl­propionitrile) as an initiator. The selective cleavage of BMAODS disulfide bonds was used to collect primary chains for the determination of the branching density (BD). The effects of initial monomer concentration, vinyl/divinyl ratio, and primary chain length on the branching and cyclization reactions were thoroughly investigated. It was found that more than 50% pendent double bonds from BMAODS were consumed in cyclization rather than in branching. The BD increased linearly with the conversion up to approximately 60% conversion. The monomer concentration was found to be the most efficient parameter in promoting branching. Increasing divinyl monomer ratio and primary chain length favored cyclization over branching. The work provides experimental evidence to support the random branching mechanism in RAFT copolymerization of vinyl and divinyl monomers.