An Easy and Efficient Route to Macrocyclic Polymers Via Intramolecular Radical−Radical Coupling of Chain Ends

Macrocyclic polystrene (PSt) was produced in high yields by an intramolecular atom transfer radical coupling reaction of the chain ends. The slow addition of the dibrominated polystyrene (BrPStBr) precursors, prepared by atom transfer radical polymerization, into a refluxing tetrahydrofuran solution of copper(I) bromide, tris[2-(dimethylamino)ethyl]amine, and copper (0) activated the alkyl bromides at the PSt chain ends, favoring an intramolecular ring closing reaction with only minor competition from intermolecular coupling. Comparison of the gel permeation chromatography traces of the BrPStBr precursor to the cyclic product showed a shift to lower apparent molecular weight values, consistent with the reduced hydrodynamic radius of the macrocycle. Quantitative activation of the chain ends was confirmed by 1H NMR spectroscopy, with the resonance due to the C(H)Br methine termini on the BrPStBr precursor absent on the NMR spectrum of the cyclic product. The cyclic structure was directly confirmed by matrix-assisted laser desorption ionization−time-of-flight spectrometry.