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...

Atom-transfer radical polymerization (ATRP) is one of the controlled/living radical polymerizations yielding well-defined (co)polymers, nanocomposites, molecular hybrids, and bioconjugates. ATRP, as in any radical process, has to be carried out in rigorously deoxygenated systems to prevent trapping of propagating radicals by oxygen. Herein, we report that ATRP can be performed in the presence of limited amount of air and with a very small (typically ppm) amount of copper catalyst together with an appropriate reducing agent. This technique has been successfully applied to the preparation of densely grafted polymer brushes, poly(n-butyl acrylate) homopolymer, and poly(n-butyl acrylate)-block-polystyrene copolymer from silicon wafers (0.4 chains/nm2). This simple new method of grafting well-defined polymers does not require any special equipment and can be carried out in vials or jars without deoxygenation. The grafting for "everyone" technique is especially useful for wafers and other large objects and may be also applied for molecular hybrids and bioconjugates.

The amount of Cu-based catalysts in atom transfer radical polymerization (ATRP) of styrene has been reduced to a few ppm in the presence of the appropriate reducing agents such as FDA approved tin(II) 2-ethylhexanoate (Sn(EH) 2 ) or glucose. The reducing agents constantly regenerate ATRP activator, the Cu(I) species, from the Cu(II) species, formed during termination process, without directly or indirectly producing initiating species that generate new chains. Moreover, the reducing agents allow starting an ATRP with the oxidatively stable Cu(II) species. The reducing/reactivating cycle may also eliminate air or some other radical traps in the system. This new catalytic system is based on regeneration of the activators for an ATRP by electron transfer and therefore was named activators regenerated by electron transfer (ARGET) ATRP. The optimum amount of reducing agent and minimal amount of ATRP Cu catalyst depend on the particular system. For example, styrene was polymerized with 10 ppm of CuCl 2 /Me 6 TREN and 100 ppm of Sn(EH) 2 resulting in a polystyrene with M n ) 63 000 (M n,th ) 64 000) and M w /M n ) 1.17.

Atom-transfer radical polymerization (ATRP) is a controlled or living radical polymerization (CRP) technique [1,2] that enables the preparation of new nanostructured materials that are not accessible by conventional free-radical polymerization (FRP). Reported herein is the ATRP of polar monomers such as (meth)acrylates and related block copolymers by means of a new initiating/catalytic method based on activators regenerated by electron transfer (ARGET) with ppm (10 À4 mol % vs. monomer) amounts of Cu catalyst. [3] ATRP [4][5][6][7] provides a simple route to many well-defined (co)polymers with precisely controlled functionalities, topologies, and compositions. [8][9][10] It has been very successfully applied to the preparation of many nanocomposites, hybrids, and bioconjugates. [11][12][13][14][15][16][17][18][19][20][21][22][23] The advantages of ATRP, in comparison with other CRP processes, include the large range of available monomers and (macro)initiators, the simplicity of reaction setup, and the ability to conduct the process over a large range of temperatures, solvents, and dispersed media. [6,7,24] ATRP (Scheme 1) is a repetitive atom-transfer process between a macromolecular alkyl halide P n ÀX and a redoxactive transition-metal complex Cu I ÀX/ligand in which P n C radicals propagate (rate constant of propagation k p ) and are reversibly formed (rate constants k a and k da ). The growing radicals also terminate by coupling or disproportionation (rate constant k t ).An inherent feature, but also a limitation of ATRP, is the presence of a catalyst (a transition-metal complex with Scheme 1. Mechanism for ATRP.