Recent advances in enantioselective ring-opening polymerization and copolymerization

Abstract

Precisely controlling macromolecular stereochemistry and sequences is a powerful strategy for manipulating polymer properties. Controlled synthetic routes to prepare degradable polyester, polycarbonate, and polyether are of recent interest due to the need for sustainable materials as alternatives to petrochemical-based polyolefins. Enantioselective ring-opening polymerization and ring-opening copolymerization of racemic monomers offer access to stereoregular polymers, specifically enantiopure polymers that form stereocomplexes with improved physicochemical and mechanical properties. Here, we highlight the state-of-the-art of this polymerization chemistry that can produce microstructure-defined polymers. In particular, the structures and performances of various homogeneous enantioselective catalysts are presented. Trends and future challenges of such chemistry are discussed.

Mechanism of Alternating Poly(lactic-co-glycolic acid) Formation by Polymerization of (S)- and (R)-3-Methyl Glycolide Using an Enantiopure Aluminum Complex

“…They, in fact, show that the preferred mechanism is M2-A based on the nucleophilic attack ( TS1 , 16.3 kcal mol –1 , Figure A) followed by ring opening ( TS2 , 15.8 kcal mol –1 , Figure B). Recall that an analogous mechanism ( fm 1 for TS1 , followed by a fm 2 for TS2 ) has been suggested as the main origin of the stereoselectivity for the rac -LA promoted by ( R )-SalBinam-Al system . Occasional regiodefects (preferred path of site A at the B-chain; see Table ) are due to the M1-A path showing the TS1 with similar energy to the RLS of B site (16.6 kcal mol –1 ; see Figure C) but with the TS2 as the RLS (18.8 kcal mol –1 ; see Figure D).…”

“…Interestingly, a lower regioselectivity was obtained when ( S )- 2 was used in combination with ( S )-MeG (corresponding to ( R )- 2 and ( R )-MeG in Figure ) due to a catalyst mismatch. Previously, we used DFT to study the origin of stereocontrol of ( R )- 2 in the isoselective ROP of rac -LA − and in the syndioselective ROP of meso -LA (Figures a and b). , Intrigued by the high regioselectivity maintained by ( R )- 2 in the ROP of MeG, we have performed an in-depth computational analysis to further inform the origin of regiocontrol and rationalize the ROP mechanism.…”

Exploiting Multimetallic Cooperativity in the Ring-Opening Polymerization of Cyclic Esters and Ethers

“…Understanding the key features of efficient multimetallic catalysts is crucial to harnessing metal–metal cooperativity and improving catalyst performance. Indeed, the ring-opening polymerization of cyclic esters and epoxides has been the focus of several review articles, ,− including those focusing on bi- and multimetallic catalysts. , Therefore, rather than providing a comprehensive overview of the field, this review highlights catalysts for the homopolymerization of ε-CL, LA, and epoxides that have delivered insight into multimetallic cooperativity, to investigate the potential origins of cooperativity and identify patterns and trends.…”

Specific Discrimination Polymerization for Highly Isotactic Polyesters Synthesis

“…Achieving specific discrimination reaction of racemic substrates is a significant challenge. − Kinetic resolution is one of the powerful methodologies to tackle this challenge, which has been widely used in medicinal chemistry and organic synthesis. − Sustained interest in the development of kinetic resolution mode over decades has led to structurally diverse chiral catalyst structures, affording highly enantioselective transformations for small molecule synthesis. − While specific discrimination polymerization to achieve highly isotactic polymers is a quite new and unexplored field. − Highly isotactic polymers usually have unique and excellent properties in material sciences, which could be synthesized from their racemic monomers via kinetic resolution [known as asymmetric kinetic resolution polymerization (AKRP)]. , However, due to the low or unsustained enantioselective control of polymerization process, examples of highly isotactic polymers obtained by AKRP are rarely reported. − …”