The concept of initiators for continuous activator regeneration (ICAR) in atom transfer radical polymerization (ATRP) is introduced, whereby a constant source of organic free radicals works to regenerate the Cu I activator, which is otherwise consumed in termination reactions when used at very low concentrations. With this technique, controlled synthesis of polystyrene and poly-(methyl methacrylate) (Mw͞Mn < 1.2) can be implemented with catalyst concentrations between 10 and 50 ppm, where its removal or recycling would be unwarranted for many applications. Additionally, various organic reducing agents (derivatives of hydrazine and phenol) are used to continuously regenerate the Cu I activator in activators regenerated by electron transfer (ARGET) ATRP. Controlled polymer synthesis of acrylates (Mw͞Mn < 1.2) is realized with catalyst concentrations as low as 50 ppm. The rational selection of suitable Cu complexing ligands {tris[2-(dimethylamino)-ethyl]amine (Me6TREN) and tris[(2-pyridyl)methyl]amine (TPMA)} is discussed in regards to specific side reactions in each technique (i.e., complex dissociation, acid evolution, and reducing agent complexation). Additionally, mechanistic studies and kinetic modeling are used to optimize each system. The performance of the selected catalysts͞reducing agents in homo and block (co)polymerizations is evaluated.controlled radical polymerization ͉ electron transfer ͉ catalysis ͉ green chemistry ͉ block copolymer T he widespread industrial application of chemical synthetic techniques is often contingent upon the efficiency with which these processes can be implemented. This dependency is particularly true in the field of controlled radical polymerization (CRP). The vast array of polymeric materials that have been produced in the last decade by atom transfer radical polymerization (ATRP) (1, 2), an especially powerful CRP technique, is striking. The extraordinary control over topologies, compositions, microstructures, and functionalities (3-6) that ATRP can provide in polymeric synthesis has led to an explosive development in nanocomposites, thermoplastic elastomers, bioconjugates, drug delivery systems, etc. (7-10).While such polymers are finding industrial applications, (11), the large-scale production of these materials has been rather limited. This fact can be attributed mostly to the high catalyst concentrations required by ATRP, often approaching 0.1 M in bulk monomer. Added expense is therefore associated with purifying any polymers generated in these homogenous reactions (12). An additional problem of industrial relevance involves the use of highly active (i.e., very reducing) ATRP catalysts. Special handling procedures are often required to remove all oxygen and oxidants from these systems. Previous research intending to streamline the process and products of ATRP has focused on maximizing the efficiency of catalyst removal or recycling through the use of ion-exchange resins (13), biphasic systems (14), immobilized͞solid-supported catalysts (12), and immobilized͞soluble h...

Equilibrium constants in Cu-based atom transfer radical polymerization (ATRP) were determined for a wide range of ligands and initiators in acetonitrile at 22 degrees C. The ATRP equilibrium constants obtained vary over 7 orders of magnitude and strongly depend on the ligand and initiator structures. The activities of the Cu(I)/ligand complexes are highest for tetradentate ligands, lower for tridentate ligands, and lowest for bidentate ligands. Complexes with tripodal and bridged ligands (Me6TREN and bridged cyclam) tend to be more active than those with the corresponding linear ligands. The equilibrium constants are largest for tertiary alkyl halides and smallest for primary alkyl halides. The activities of alkyl bromides are several times larger than those of the analogous alkyl chlorides. The equilibrium constants are largest for the nitrile derivatives, followed by those for the benzyl derivatives and the corresponding esters. Other equilibrium constants that are not readily measurable were extrapolated from the values for the reference ligands and initiators. Excellent correlations of the equilibrium constants with the Cu(II/I) redox potentials and the carbon-halogen bond dissociation energies were observed.

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Atom transfer radical polymerization (ATRP) equilibrium constants (K(ATRP)) were determined using modified Fischer's equations for the persistent radical effect. The original Fischer's equations could be used only for low conversion of Cu(I) to X-Cu(II) and consequently for relatively low values of K(ATRP). At higher conversion to X-Cu(II) (>10%) and for larger values of K(ATRP) (>10(-)(7)), modified equations that take into account the changes in catalyst and initiator concentrations should be used. The validity of new equations was confirmed by detailed kinetic simulations. UV-vis spectrometric and GC measurements were used to follow the evolution of X-Cu(II) species and the initiator concentration, respectively, and to successfully determine values of K(ATRP) for several catalysts and alkyl halides. The effect of structure on reactivities of ATRP components is presented.