CHAPTER 19. Influence of Noncovalent Interactions in Catalytic Ring-opening Polymerization Processes

Interest in noncovalent interactions in ring-opening polymerization (ROP) processes has burgeoned in recent years. Although the presence of these interactions has been proposed in several ROP mechanisms, the field where the role of noncovalent interactions has been emphasized and used for the design of catalysts is the so-called H-bonding catalysts. Both acidic and basic/nucleophilic species can promote the ROP of cyclic monomers via an H-bonding mechanism, as supported by theoretical studies and experimental evidence. In these catalytic systems, the combination of an H-bonding donor (HBD) and an H-bonding acceptor (HBA) leads to a bifunctional catalytic system in which the HBD activates the monomer and the HBA the initiating/propagating alcohol by H-bonding interactions. In most cases, the polymerization takes place under mild conditions with a living character. Very good control of the polymerization is achieved and narrowly dispersed polymers of predictable molecular weights are obtained, although the molecular weights are low to moderate. This type of catalyst is also effective in copolymerization processes. Apart from H-bonding, other noncovalent interactions have hardly been explored for ROP. This is an exciting area that is only in its infancy, and the exploration of the influence of other noncovalent interactions and the search for more active systems while maintaining good polymerization control are still open challenges.