Recent Advances in Metal‐Mediated Stereoselective Ring‐Opening Polymerization of Functional Cyclic Esters towards Well‐Defined Poly(hydroxy acid)s: From Stereoselectivity to Sequence‐Control

Abstract

Poly(hydroxy acid)s are a family of biocompatible and (bio)degradable polyesters with various outcomes in different domains of application. To date, poly(hydroxy acid)s are best prepared by ring‐opening polymerization (ROP) of the corresponding cyclic esters. Using racemic chiral monomers featuring side‐chain groups enables to access, providing a stereoselective catalyst/initiator system is implemented, stereoregular functional polymers, thereby improving their physico–chemical properties, and ultimately, widening their range of uses. Here, we highlight a few important advances in metal‐mediated stereoselective ROP of cyclic esters towards the synthesis of (functional) stereoregular poly(hydroxy acid)s that have recently been disclosed, emphasizing on (functional) β‐ and γ‐lactones, diolide and O‐carboxyanhydride (OCA) monomers and yttrium‐based catalysis. Fine‐tuning of the substituents flanked on the catalyst ligand enables reaching poly(hydroxy acid)s with syndiotactic and also isotactic microstructures. The stereocontrol mechanisms at work and their probable origin, relying on steric but also electronic factors imparted in particular by the ligand substituents, are discussed. Taking advantage of such stereoselective ROPs, original copoly(hydroxy acid)s with gradient or alternated patterns then become accessible from the use of mixtures of chemically different, oppositely configured enantiopure monomers.

High-performance pan-tactic polythioesters with intrinsic crystallinity and chemical recyclability

“…Therefore, higher tacticity leads to a crystalline polymer with a higher T m , whereas stereo-disordered or atactic polymers having a random arrangement of stereocenters or even modestly tactic polymers are often amorphous. This long-standing rule highlights the importance of achieving a high degree of stereochemical control in polymer synthesis and often represents a highly demanding task for many polymerization systems, which has continuously challenged polymer chemists and captivated their attention and efforts (32)(33)(34)(35)(36). However, there are a few exceptions to this rule.…”

Controlled Ring-Opening Polymerization of O-Carboxyanhydrides to Synthesize Functionalized Poly(α-Hydroxy Acids)

“…38 Cheng and coworkers dominated the advancement of therapeutics delivery-driven polymerizations of functionalized OCAs as seen in work presenting ROPs of serine-derived 2, tyrosine-derived 7, and disulfide-containing camptothecin-poly(7) conjugate, all of which achieved impressively low Đ values with potential biological and pharmaceutical applications. 14,39,40 In contrast to the noticeable drop in reactivity of LA when pendant functionalities are introduced, 19,20,41,42 OCA demonstrates relatively stable reactivity in the presence of aliphatic and aryl functional groups. Therefore, it is not surprising that copolymers of OCAs can be easily synthesized.…”

The rise of bio-inspired polymer compartments responding to pathology-related signals

“…82,94 Starting from cyclic monomers, ring-opening polymerization (ROP) techniques allow the synthesis of polymers with well-defined molecular weight and chemical composition. [95][96][97][98][99] For example, polyesters have been synthesized from cyclic esters (lactones), polysiloxanes from cyclosiloxanes, and polyamides from cyclic amides (lactams) ( Tables 1 and 2). However, the ROP mechanism and the polydispersity of the resulting polymer are strongly influenced by the type and concentration of the monomer and the catalyst which calls for extensive optimization procedures.…”