This work reports a facile and versatile ring-opening metathesis polymerization of three-and four-armed star-shaped poly(ε-caprolactone) (PCL) macromonomers bearing a norbornenyl group at each chain end using Grubbs' third-generation catalyst under diluted condition to obtain graft polymers (GPs) comprising densely arrayed three-and four-armed cage-shaped grafted PCLs (GPCLs) with narrow dispersity (1.19−1.35) and a controllable number of cage repeating units up to 40 (molecular weight: ∼320 000 g mol −1 ). The GPCLs were characterized using nuclear magnetic resonance spectroscopy, size exclusion chromatography, and matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. The cyclopolymerization proceeded via repetitive rapid intramolecular reactions to form cage-shaped units followed by slow intermolecular propagation. This synthesis was applicable to star-shaped poly(L-lactide), poly(trimethylene carbonate), and poly(ethylene glycol). Investigating the structure−property relationships regarding crystallization behavior, hydrodynamic diameter, and viscosity revealed that cageshaped topological side chains reduced the chain dimensions and mobility compared to their linear and cyclic counterparts.
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