Cooligomerization of γ-butyrolactone with (meth)acrylates catalyzed by N-heterocyclic carbene: Low possibility of hybrid copolymerization

Copolymerization between lactones and vinyl monomers has significant implications for the synthesis of new polymeric materials; however, a highly reactive cyclic monomer, e.g., epsilon-caprolactone (CL), leads to a copolymeric product but with a complex structure remaining to be elucidated. Herein, we present cooligomerizations of gamma-butyrolactone (gamma BL), a low-polymerizable cyclic monomer, with (meth)acrylates catalyzed by an N-heterocyclic carbene (NHC) under conditions in which no reaction occurs in the absence of either comonomer. Several experimental studies indicate that the product is not a hybrid cooligomer with an ester linkage in the main chain but a graft cooligomer. The reaction mechanism involves the generation of the gamma BL enolate by the NHC to initiate oligomerizations of gamma BL and (meth)acrylates followed by the transesterification of oligo (gamma BL) with an ester unit of (meth)acrylates. These results prompted us to investigate the previously reported structure of copolymer of CL and methyl methacrylate obtained by a phosphazene base catalyst. The hydrolysis experiment revealed that the copolymeric product turned out not to be a hybrid random copolymer.

Automated summary

Experimental studies revealed that gamma-butyrolactone (γ-BL) undergoes graft co-oligomerization with (meth)acrylates catalyzed by N-heterocyclic carbene (NHC), instead of hybrid co-oligomerization with ester linkage in the main chain, as initially hypothesized.