Cyclic polymers and catenanes by atom transfer radical polymerization (ATRP)

The topologically interesting structures of cyclic polymers, catenanes and other macrocycles are of much interest for their unique chemical and physical properties. However, it is a challenge to design synthetic routes that afford controlled ring structures and connectivity, which is why the practical applications of these materials have not been explored. This review describes the advantages and disadvantages of ring expansion and ring closure methods for preparing cyclic polymers. This review also aims to provide a concise overview of the recent techniques of cyclization specifically by ring closure reactions from polymers grown primarily by atom transfer radical polymerization (ATRP). The ring closure techniques covered here are atom transfer radical coupling (ATRC), copper-catalyzed Huisgen azide-alkyne cycloaddition, Diels-Alder cycloaddition and alkylation of carboxylate salts to form esters. Ring expansion and ring closure methods have also been used in the preparation of polymer catenanes. A combination of ATRP and ATRC has been applied to the synthesis of homopolymer and block copolymer catenanes using a supramolecular template with ATRP initiators.