Zero-valent bimetallic iron/copper catalyzed SET-LRP: A dual activation by zero-valent iron

摘要

In this work, bimetallic zero-valent metal (Fe(0) powder and Cu(0) powder) was used to mediate the single electron transfer-living radical polymerization (SET-LRP) of methyl methacrylate at 25 °C in dimethyl sulfoxide. Different feed ratios of [Fe(0)] _0/[Cu(0)] _0 (0/1.5, 0.5/1, 0.75/0.75, 1/0.5, and 1.3/0.2) were explored. With the increase of Fe(0) feed, the polymerization rate was mildly depressed with a prolonged induction period. While, the control over the molecular weights was improved upon the increase of Fe(0). A best control (initiation efficiency = 91%) was achieved at [Fe(0)] 0/[Cu(0)] 0 = 1/0.5. A further increase of Fe(0) to the feed ratio of [Fe(0)] _0:[Cu(0)] _0 = 1.3: 0.2 led to a uncontrolled polymerization. Explorations of available solvents and ligands for this polymerization confirmed the SET-LRP mechanism. It was suggested that Fe(0) might act as a dual role in this process: one was the activation agent for Cu(0), which favored a better control over the molecular weights; The other was an alternative catalyst for the activation of R-X or P _n-X to generate radicals, which assured a comparable polymerization rate as that of Cu(0). This work provided an alternative and economical catalyst for SET-LRP, and would eventually reinforce the SET-LRP technique.