Catalyst Solubility and Experimental Determination of Equilibrium Constants for Heterogeneous Atom Transfer Radical Polymerization

Abstract

The solubilities of heterogeneous atom transfer radical polymerization (ATRP) catalysts are determined for the first time and used to calculate previously unquantified ATRP equilibrium constants (K ATRP). These new data are essential for understanding, modeling, and designing ATRP processes with low catalyst concentrations. K ATRP values for CuIBr/1,1,4,7,10,10-hexamethyltriethylenetetramine (CuIBr/HMTETA) and CuIBr/N,N,N‘,N‘,N‘ ‘-pentamethyldiethylenetriamine (CuIBr/PMDETA) are 8.66 × 10-6 and 1.44 × 10-6, respectively. The limited solubility of the CuIBr/HMTETA catalyst explains why large reductions in metal salt concentration can be made without affecting polymerization rates. Catalyst solubility and polymerization rate increase with ligand concentration. In contrast, increasing the metal salt concentration in excess of the ligand's causes a drop in catalyst solubility. This unexpected observation is attributed to the formation of insoluble catalyst networks (gels). The solubility data point to differences in the ionic character of the catalyst complexes formed. The following solubility trend is observed at ATRP conditions (toluene, 90 °C): CuIBr/PMDETA ≫ CuIIBr2/PMDETA > CuIIBr2/HMTETA > CuIBr/HMTETA.

Tuning the Solubility of Copper Complex in Atom Transfer Radical Self-Condensing Vinyl Polymerizations to Control Polymer Topology via One-Pot to the Synthesis of Hyperbranched Core Star Polymers

“…Reactions of mixed initiators in various single solvents at various temperatures and ratios of copper/ligands were performed based on previous literature [56][57][58][59][60]. The Cu(I) complexes were prepared in situ under a N2 atmosphere by adding deoxygenated solvent (2 mL) to Bpy (0.2 mmol), TEMPO (1.0 mmol), and CuBr (0.1 mmol) in a Schlenk flask.…”

“…Besides, cupric complexes (i.e., Cu(I)/ligand or Cu(II)/ligand) have significantly different solubilities in various solvents at various temperatures [56]. To the best of our knowledge, there have been no previous reports of manipulating differences in solubility to control polymer topologies through variations in temperature or solvent in a one-pot procedure.…”

Kinetic Modeling of ICAR ATRP

“…Finally, solubility limits for the transition metal complexes involved were not considered, since the ICAR ATRP process is performed using a very low catalyst concentration (ppm level) at which such effects can be neglected. [41,42] …”

Pyrrolidin-2-one Structure Derivatives as Novel Ligands for Copper-based Atom Transfer Radical Polymerization (ATRP)

“…33 The apparent polymerization rate constant, k p app ¼ 7:83 Â 10 À5 S À1 , for ATRP of MMA catalyzed by CuBr/(N-butyl) 3 TEDP at 90 C were calculated from the Arrhenius plot, which was some lower than the value (k p app ¼ 1:13 Â 10 À4 S À1 at 90 C) for ATRP of MMA catalyzed by CuBr/PMDETA. 46 According to the above result, a conclusion could be deduced that the activity of (N-butyl) 3 TEDP as ligand was more or less lower as the ones of PMDETA as ligand for Cu-based ATRP. This phenomenon can be possibly ascribed to the bulk alkyl substitute and pyrrolidinone structure of (N-butyl) 3 TEDP.…”