Determination of ATRP Equilibrium Constants under Polymerization Conditions

Abstract

Atom transfer radical polymerization (ATRP) equilibrium constants ( K ATRP ) were measured during polymerization of methyl acrylate (MA) with Cu I Br/Cu II Br 2 in either dimethyl sulfoxide (DMSO) or acetonitrile (MeCN) in the presence of either tris(2-pyridylmethyl)amine (TPMA) or tris[2-(dimethylamino)ethyl]amine (Me 6 TREN) as the ligand and with ethyl 2-bromopropionate as the initiator. The ln( K ATRP ) values changed linearly with the volume fraction of solvents in the reaction medium, allowing extrapolation of the values for K ATRP to bulk conditions, which were 2 × 10 –9 and 3 × 10 –8 for TPMA and Me 6 TREN ligands at 25 °C, respectively. The temperature effect on K ATRP values was studied in MA/MeCN = 1/1 (v/v) with TPMA as the ligand in the temperature range from 0 to 60 °C. The K ATRP values increased with temperature providing Δ H = 36 kJ mol –1 in MeCN.