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

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 [ n BuMe 2 NCH 2 CH 2 N n BuMe 2 ]Br 2 (DBTMEDA)Br 2 has been investigated. The catalyst (DBTMEDA)Br 2 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.