Macrocyclic polymers: Synthesis, purification, properties and applications

Cyclic polymers present a topology that differ significantly from their linear counterparts due to their circular structure and therefore, the lack of chain ends. These simple characteristics are responsible for important unique properties (e.g. lower intrinsic and melt viscosity, lower hydrodynamic volumes, slower degradation profiles, increased blood circulation times and more selective bioaccumulation) thanks to which the cyclic polymers are today a vanguard in macromolecular chemistry. However, the preparation of cyclic polymers with high topological purity and in large quantities is challenging, therefore demanding the continuous development of synthetic methods. Advances in organic chemistry and the development of new catalytic systems has allowed the field of cyclic polymers to expand enormously in recent decades. In this review, ring closure and ring expansion polymerization strategies are described along the milestones that have characterized the evolution of cyclic (bio)polymer chemistry over the years. We also focus on very recent advances and state-of-the-art techniques for the synthesis and purification of cyclic polymers and provide an overview of properties and applications of cyclic polymers in different fields.