Determination of ATRP Equilibrium Constants under Polymerization Conditions

Atom transfer radical polymerization (ATRP) equilibrium constants (<i>K</i>_ATRP) were measured during polymerization of methyl acrylate (MA) with Cu^IBr/Cu^IIBr₂ in either dimethyl sulfoxide (DMSO) or acetonitrile (MeCN) in the presence of either tris­(2-pyridylmethyl)­amine (TPMA) or tris­[2-(dimethylamino)­ethyl]­amine (Me₆TREN) as the ligand and with ethyl 2-bromopropionate as the initiator. The ln­(<i>K</i>_ATRP) values changed linearly with the volume fraction of solvents in the reaction medium, allowing extrapolation of the values for <i>K</i>_ATRP to bulk conditions, which were 2 × 10^–9 and 3 × 10^–8 for TPMA and Me₆TREN ligands at 25 °C, respectively. The temperature effect on <i>K</i>_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 <i>K</i>_ATRP values increased with temperature providing Δ<i>H</i> = 36 kJ mol^–1 in MeCN