Polyether/Polythioether Synthesis via Ring-Opening Polymerization of Epoxides and Episulfides Catalyzed by Alkali Metal Carboxylates

Abstract

Alkali metal carboxylates were evaluated as simple and green catalysts for the ring-opening polymerization (ROP) of various epoxides (e.g., alkyl-substituted epoxides and glycidyl ethers) and episulfides (alkyl-substituted episulfides and thioglycidyl ethers). The thus-produced functional polyethers (end-functionalized polyethers, block copolyethers, polyether–polyester block copolymers, topologically unique polyethers, and isotactic-enriched polyethers) and polythioethers featured well-defined structures and controlled molecular weights (M n,SEC = 1.0–32 kg mol–1). The most effective catalyst was identified as cesium pivalate, and the variation of carboxylate moieties and alkali metal cations enabled the tuning of acid/base characteristics and thus allowed one to control polymerization behavior and expand the scope of functional monomers and initiators. Kinetic analysis confirmed the controlled/living nature of the polymerization process, while mechanistic studies revealed that carboxylate moieties did not directly initiate the ring-opening of epoxide monomers via nucleophilic attack but rather activated the alcohol initiators/chain ends via H-bonding and thus rendered the corresponding OH groups sufficiently nucleophilic to attack the alkali metal cation-activated epoxides.

Rare Earth Metal‐Containing Ionic Liquid Catalysts for Synthesis of Epoxide/Cyclic Anhydride Copolymers

“…Of these salts, cesium pivalate has been shown to be an active catalyst and has been used to make a wide range of polyesters through the target ROCOP (Figure 2A). [3][4][5][6][7][8] While Cs-pivalate has been shown to exhibit the highest activity of a series of alkali metal carboxylates tested for copolymerization of various monomer pairs, these polymerizations were met with some challenges such as long reaction times, the need for an initiator along with the catalyst, and airfree conditions. Additionally, extremely high monomer loadings are needed to acquire high molecular weight polymers (> 30 kDa).…”

Isotactic-Rich Polythioethers Synthesized from Asymmetric Ring-Opening Polymerization of Racemic Terminal Thiiranes

“…Analogous to epoxides, thiiranes are capable of synthesizing polythioethers via ring-opening polymerization (ROP). − However, compared to the significant achievements made in epoxide-involved asymmetric (co)­polymerization, thiirane-involved asymmetric (co)­polymerization has drawn less attention for fabricating isotactic-rich sulfur-containing polymers. For example, the synthesis of isotactic thiirane-derived polythioesters was obtained using chiral propylene sulfide for copolymerization with succinic thioanhydride .…”

Alkali metal carbonate catalyzed copolymerization of anhydrides and epoxides: a simple, efficient and versatile approach to well-defined alternating polyesters

“…Very recently, alkali metal carboxylates have been demonstrated as simple and green initiators for ROAC. [33][34][35][36][37][38] However, a chainend elimination side reaction limits the achievement of endfunctional polymers. Simpler ROAC catalysts for the facile synthesis of end-functional polyesters is highly desirable.…”