Organocatalytic Ring-Opening Polymerization of Methyl-Substituted Glycolides

Aliphatic polyesters derived from the ring-opening polymerization (ROP) of cyclic esters offers access to sustainable, depolymerizable, and renewable materials. Herein, we report the first organocatalytic ROP of dimethyl glycolide (DMG) and tetramethyl glycolide (TMG), synthesized from biobased α-hydroxy acids via an acylation/cyclization pathway. Using a metal-free catalytic system comprising phosphazene base (P₂-Et), thiourea (TU), and benzyl alcohol (BnOH) as the initiator, racemization-free poly-(dimethylglycolide) (PDMG) and poly-(tetramethylglycolide) (PTMG) were synthesized at room temperature. The resulting polyesters exhibited predictable molecular weights, low dispersity indices (Đ ≤ 1.25), and no transesterification, confirmed by ¹H NMR, SEC, and MALDI-TOF analyses. Mechanistic studies revealed distinct activation pathways: PDMG polymerization proceeds via TU imidate anion activation mechanism, while PTMG follows the conventional initiator/chain-end activation mechanism. Both polymerization processes demonstrated typical first-order kinetics. Computational modeling identified two key transition states (TSs) in the ROP mechanism: TS-1, involving the nucleophilic attack of BnOH on the carbonyl carbon of DMG or TMG, and TS-2, which involves the subsequent ring opening of the cyclic ester. Importantly, PDMG and PTMG can be quantitatively depolymerized into their respective monomers, enabling complete material recycling. This study establishes a sustainable approach for designing renewable polyesters with potential lifecycle management.