Controlled copolymerization of the functional 5-membered lactone monomer, α-bromo-γ-butyrolactone, via selective organocatalysis

Abstract

The selective nature of organic catalysts has been exploited to synthesize copolymers of the functional monomer, α-bromo-γ-butyrolactone (αBrγBL), with trimethylene carbonate (TMC), 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC) and ε-caprolactone (εCL) with excellent control. The high control is attributed to high selectivity and reactivity at ambient reaction temperatures, which suppresses the degree of side reactions (e.g., transesterification) that inherently plague this class of co-monomers. In particular, good results were obtained using diphenyl phosphate (DPP) as a catalyst, resulting in copolymers with low dispersities (ÐM) (i.e., approximately 1.08) and number average molecular weights (Mn) of approximately 20,000 g/mol. The high control opened the possibility to construct more complex polymeric structures, exemplified via the synthesis of a multifunctional triblock copolymer composed of AOMEC as the center block, flanked with a statistical copolymer consisting of ɛCL and αBrγBL. The subsequent grafting of methyl acrylate (MA) via Cu(0)-mediated CRP on the copolymers resulted in graft copolymers with a final ÐM of less than 1.2.