Green synthesis of poly ε-caprolactone using a metal-free catalyst via non-covalent interactions†

Abstract

The ring-opening polymerization (ROP) of ε-caprolactone (CL) catalyzed by a metal-free initiator N,N′-dibutyl-N,N,N′,N′-tetramethylethane1,2-diammonium bromide [ⁿBuMe₂NCH₂CH₂NⁿBuMe₂]Br₂ (DBTMEDA)Br₂ has been investigated. The catalyst (DBTMEDA)Br₂ promotes polymerization under mild conditions without any external initiator. Polymerization was demonstrated in a controlled and living manner, producing PCLs with a precisely controlled molecular weight of up to 50 kDa with narrow polydispersity. Density Functional Theory (DFT) calculations indicated the involvement of a C–H⋯O type non-covalent interaction between DBTMEDA cations and the carbonyl group of ε-CL in the monomer activation step. Remarkably, DBTMEDA can also be easily recovered and reused for up to six consecutive cycles without an appreciable decrease in catalytic activity.