Reversible Addition-Fragmentation Chain Transfer (RAFT) Polymerization in an Inverse Microemulsion: Partitioning of Chain Transfer Agent (CTA) and Its Effects on Polymer Molecular Weight

The effects of CTA partitioning between the aqueous and oil phases on resulting molecular weight in reversible addition-fragmentation chain transfer in inverse microemulsion polymerization (RAFT-IMEP) of N,N-dimethylacrylamide (DMA) have been investigated. Four trithiocarbonate-based CTAs (2-(1-carboxy-1-methylethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (CM P), 2-(ethylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (EM P), 4-cyano-4-(ethylsulfanylthiocarbonylsulfanyl)pentanoic acid (CEP), and 2-(dodecylsulfanylthiocarbonylsulfanyl)-2-methylpropionic acid (DMP)) with different solubilities in the aqueous phase were chosen for these studies. The experimentally determined molecular weights were progressively higher than theoretically predicted as CTA partitioning into the organic phase increased. By comparing results with aqueous RAFT control experiments conducted at the same temperature and with the same CTAs and initiators, we demonstrate that the mole fraction of CTA partitioned into the aqueous phase prior to RAFT-IMEP can be substituted directly as the efficiency factor, gamma, for RAFT agent utilization allowing accurate predictions of molecular weight at specified conversions.