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Abstract

This contribution investigates organopolymerization of five multifunctional γ-butyrolactone-based monomers, including bifunctional (endocyclic double bond, lactone ring) dihydrofuran-2(3H)-one (FO), 3-methylfuran-2(5H)-one (3-MFO), and 5-methylfuran-2(5H)-one (5-MFO), as well as trifunctional (endocyclic or exocyclic double bond, lactone ring, hydroxyl group) 3-(hydroxymethyl) furan-2(5H)-one (3-HMFO) and β-hydroxy-α-methylene-γ-butyrolactone (βHMBL). The complexity of the reaction under nucleophilic and basic conditions using N-heterocyclic carbene (NHC) and superbase organic catalysts increases dramatically on going from the bifunctional monomers to the trifunctional ones. Thus, the polymerization of the parent FO leads to a vinyl-addition polymer, while the reaction of the base catalysts with the two methyl-substituted derivatives, 3-MFO and 5-MFO, affords predominately a trimer and dimer, respectively. The polymerization of trifunctional 3-HMFO gives a poly(vinyl–ether lactone) copolymer structure, via two different types of base activation mechanisms and a combination of Michael and ox-Michael additions and proton transfer processes. The polymerization of βHMBL has the highest degree of the complexity in this monomer series, due to its presence of both the reactive exocyclic double bond and hydroxyl group, producing a branched vinyl–ether lactone copolymer structure having six different types of substructural units. The results reveal multiple types of reaction pathways and their mechanistic crossovers involved in the βHMBL polymerization, including conjugate Michael and oxa-Michael additions and proton transfer processes, as well as ene-type dehydration reactions, enabled by proton transfer.