Mechanistic insights into the incorporation of higher alpha-olefins into acrylate copolymers via photoATRP

Abstract

Visible light-induced photo atom transfer radical polymerization (photoATRP) is a highly effective and environmentally friendly approach for synthesizing copolymers of polar and non-polar monomers, offering outstanding properties such as printability, adhesion, paintability, pour point depression, and viscosity index improvement. In this study, simultaneous reverse and normal initiation (SR & NI) photoATRP of acrylates (polar monomers) and higher α-olefins (C₈–C₁₂) (non-polar monomers) was conducted using Cu^IIBr₂/L (L = N,N,N′,N′′,N′′-pentamethyldiethylenetriamine (PMDETA), tris(2-aminoethyl)amine (Tren), and 2,4,6-tripyridyl-(2-pyridyl)-1,3,5-triazine (TPT)) complexes. Radical generation takes place both from the photoinitiator (PI), namely phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO), and via direct photolysis of Cu^II/L complexes to initiate polymerization. Copolymers with a controlled molecular weight (MW), narrow dispersity (Đ ≤ 1.13), and high incorporation of α-olefins (up to 30%) were obtained. Kinetic analysis revealed a first-order, controlled, and living radical polymerization behavior. Furthermore, density functional theory (DFT) calculations were employed to gain mechanistic insights into the polymerization behavior via two distinct pathways, leading to the production of two different products, PCA2 and PCB2 with activation energy barriers of 14.3 kcal mol⁻¹ and 17.8 kcal mol⁻¹, respectively.