Isomeric Dicyclic Polymers via Atom Transfer Radical Polymerization and Atom Transfer Radical Coupling Cyclization

Abstract

Intramolecular terminal–terminal coupling of the star polymers with a defined number of arms would form multiple cyclic polymers. If the core structure is asymmetric in its composition, the statistically occurred coupling reactions may generate isomerism in the multicyclic products. Herein, this phenomenon was confirmed by applying well-defined star polystyrenes, (S)4, with four arms and a compositional asymmetrical core. The star polymers were prepared by ATRP of styrene using a designed initiator that had a −S–S– center group and four ester groups. Then, intramolecular atom transfer radical coupling (ATRC) reactions among four Br terminals of the star polymers were conducted under a high dilute condition. Depending on how the coupling occurred statistically, the obtained dicyclic polymers contained two topological isomers of which two cyclic polymeric units were linked by different manners. The presence of two isomers was confirmed by cleavage of the disulfide bonds, and the content of each isomer was evaluated. A complete cyclization of the (S)4 and structure of topological isomers were characterized by size exclusion chromatography, 1H NMR and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, and different cleaving strategies.