Effect of variation of [PMDETA]₀/[Cu(I)Br]₀ ratio on atom transfer radical polymerization of n‐butyl acrylate

A kinetic study was conducted to examine the effect of varying the ratio of ligand to transition metal in a Cu(I)Br/ N,N,N ′, N ″, N ″‐pentamethyldiethylenetriamine (PMDETA) catalyst system for atom transfer radical polymerization (ATRP) of n ‐butyl acrylate ( n BA) using methyl 2‐bromopropionate as the initiator. Experimental molecular weights were higher than theoretical when low molecular weight polymers were targeted at low ratios of [PMDETA] 0 /[Cu(I)Br] 0 (< 1), indicating inefficient initiation/deactivation. A downward curvature in the plot of M n versus conversion was observed at high monomer conversion when targeting high molecular weight polymers. This deviation became more significant when an excess of ligand was used, indicating a contribution of chain transfer to ligand. The maximum rate of polymerization was obtained at [PMDETA] 0 /[Cu(I)Br] 0 ≈ 0.5 for bulk ATRP of n BA; however for polymerization in the presence of 10 vol% DMF, the maximum appeared at the ratio ≈ 1:1. Addition of acetone or DMF improved solubility of Cu(II) complex, which consequently improved the level of control over the polymerization at low ratios of [PMDETA] 0 /[Cu(I)Br] 0 , but also reduced the reaction rate. The polymerization rate increased with temperature, but at the expense of increased polydispersities.