(226k) Quantitative Study on Branching Behavior in RAFT Copolymerization of a Vinyl/Divinyl System
Outstanding chemical and mechanical properties make highly branched polymers (HBP) one of the most intensively studied objects of the past few decades. Synthesis of HBPs via controlled/living radical copolymerization of vinyl and divinyl systems are of interest because of their facile synthetic routes. Although theoretical studies on the branching formation mechanism have been carried out, these theories require experimental evidences for validation. Herein, a series of HBPs were synthesized by reversible addition-fragmentation chain transfer (RAFT) solution copolymerization. Methyl methacrylate (MMA) and a disulfide-based dimethacrylate (DSDMA) cross-linker were used for the synthesis at 70 °C in toluene. 2-cyano-2-propyl dodecyl trithiocarbonate was chosen as a RAFT chain transfer agent and 2, 2’-azobis(2-methylpropionitrile) as an initiator. The selective cleavage of disulfide bonds of DSDMA at the cross-linkages enabled us to determine the weight fraction of branched polymers with different primary chains. Branching density (BD) and cyclization density (CD) were also determined accordingly by varying the initial monomer concentration between 15-45% and using [MMA]/[DSDMA] ratios of 100:(0.5, 1, 1.5). It was found that a higher monomer concentration enhances branching rather than cyclization, while increasing the divinyl content both increases BD and CD. Furthermore, cyclization is preferred for a longer primary chain length. We verified the random branching characteristics of RAFT copolymerization in vinyl/divinyl systems. This work has developed a feasible method to study the branching behavior and provided insight into the mechanism of RAFT copolymerization at the pre-gel stage.