Recent developments in entropy-driven ring-opening metathesis polymerization: Mechanistic considerations, unique functionality, and sequence control

Entropy-driven ROMP (ED-ROMP) involves polymerization of olefin-containing macrocyclic monomers under entropically favorable conditions. Macrocycles can be prepared from a variety of interesting molecules which, when polymerized, impart unique functionality to the resulting polymer backbone such as degradable linkages, biological moieties, crystallizable groups, or supramolecular hosts. In addition, the sequence of atoms in the cyclic monomer is preserved within the polymer repeating units, allowing for facile preparation of sequence-defined polymers. In this review article, we consider how the mechanism of ROMP applies to ED polymerizations, how olefinic macrocycles are synthesized, and how polymerization conditions can be tuned to maximize conversion. Recent works in the past 10 years are highlighted, with emphasis on methods which can be employed to achieve fast polymerization kinetics and/or selective head-to-tail regiochemistry, thus improving polymerization control. ED-ROMP, with its unique capability to produce polymers with well-defined polymer backbone microstructure, represents an essential complement to other, well-established, metathesis methodologies such as ROMP.