Synthesis and Ring-Opening Polymerization of Bisubstituted ε-Caprolactones Bearing Aryl and Cyano Groups

A series of novel 4,4-bisubstituted ε-caprolactone (CL) monomers with pendent aryl and cyano groups were designed and effectively synthesized from commercially available aryl nitriles with methyl acrylate. The synthetic process relies on a tandem double Michael addition-Dieckmann condensation-Krapcho decarboxylation in a one-pot system, followed by a subsequent Baeyer-Villiger oxidation. Furthermore, the ring-opening polymerization of these obtained CL monomers was successfully achieved under mild reaction conditions, employing p-methylbenzyl alcohol as the initiator and 1,5,7-triazabicyclo [4.4.0] dec-5-ene (TBD) as an organocatalyst. The glass transition temperatures (T_g) of the resultant polyesters were in the range of 45 to 95 °C, strongly dependent on the cyano and aryl substituents. More importantly, the resultant polyesters could be effectively depolymerized in alkali condition to generate the corresponding ε-hydroxy caproic acids with excellent yields, which could be transformed back to their starting monomers via subsequent lactonization process, thus establishing their circular life cycle.