A versatile ring-closure method for efficient synthesis of cyclic polymer and tadpole-shaped copolymer

In this study, an efficient strategy was presented to prepare monocyclic polymers via combination of reversible addition-fragmentation chain transfer (RAFT) polymerization and light-induced cycloaddition reaction, and tadpole-shaped copolymer was further synthesized via ring-opening polymerization (ROP) using cyclic poly-styrene (C-PS) as macroinitiator. A series of well-defined alpha, omega-hetero bifunctional homopolymers with furan-protected maleimide and o-methylbenzaldehyde terminals, including polystyrene (PS), poly (N, N-dimethyla-crylamide) (PDMA) and poly (N-isopropylacrylamide) (PNIPAAm) were prepared via RAFT polymerization. After deprotection, highly active maleimide group at the end of linear polymer coupled intramolecularly with pho-toenol structure (photoisomer of o-methylbenzaldehyde) via Diels-Alder cycloaddition reaction under 365 nm UV irradiation in dilute solution, leading to the formation of cyclic polymer. The monocyclic polymers were characterized with H-1 NMR, UV-Vis spectroscopy, gel permeation chromatography (GPC) and MALDI-TOF MS. Furthermore, the C-PS containing hydroxyl group was used as macroinitiator to prepare tadpole-shaped copol-ymer CPS-b-PCL via the ROP of epsilon-caprolactone.