Atom Transfer Radical Polymerization (ATRP): Current Status and Future Perspectives

Determination of ATRP Equilibrium Constants under Polymerization Conditions

Atom transfer radical polymerization (ATRP) equilibrium constants (K_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(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 Me₆TREN 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 ΔH = 36 kJ mol^-1 in MeCN.

Application of (1)H DOSY for Facile Measurement of Polymer Molecular Weights

To address the practical issues of polymer molecular weight determination, the first accurate polymer weight-average molecular weight determination method in diverse living/controlled polymerization via DOSY (diffusion-ordered NMR spectroscopy) is reported. Based on the linear correlation between the logarithm of diffusion coefficient (log D) and the molecular weights (log Mw), external calibration curves were created to give predictions of molecular weights of narrowly-dispersed polymers. This method was successfully applied to atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT), and ring-opening metathesis polymerization (ROMP), with weight-average molecular weights given by this method closely correlated to those obtained from GPC measurement.