A straightforward approach for the one-pot synthesis of cyclic polymers from RAFT polymers via thiol–Michael addition

Abstract

Cyclic polymers have aroused more research interests in recent years. However, an effective synthetic approach for cyclic polymers is still lacking, and developing a novel and effective approach for the synthesis of cyclic polymers is highly desirable. Herein, a straightforward approach for the effective synthesis of cyclic polymers is illustrated. First, reversible addition–fragmentation chain transfer (RAFT) polymerization was implemented using a chain transfer agent with a furan-protected maleimide at the R group. The linear precursor for RAFT, poly(methyl methacrylate) (PMMA), was then dissolved in solvent with a highly dilute concentration and heated to 110 °C to de-protect the maleimide followed by aminolyzing the thiocarbonylthio to a thiol group at room temperature. Upon the release of the thiol, simultaneous intramolecular ring closure via thiol–maleimide Michael addition happened to afford cyclic PMMA. The cyclic PMMA was subjected to SEC, NMR and MALDI-TOF mass spectroscopy, which provided convincing evidence for successful preparation. The yield of the cyclic PMMA reached 80% without any purification. The versatility of this one-pot approach was verified by using either a functional monomer or a trithiocarbonate as the chain transfer agent. Interestingly, the linear RAFT polymer mediated by the symmetric trithiocarbonate chain transfer agent produced a cyclic polymer with half the molecular weight due to its intrinsic mechanism. This work undoubtedly offers a novel and effective approach for synthesizing cyclic polymers. The preparations of other topological cyclic polymers are also envisioned by employing different structures of chain transfer agents through this approach.