Why Do We Need More Active ATRP Catalysts?

Abstract

Atom transfer radical polymerization (ATRP) is a staple technique for the preparation of polymers with well‐defined architecture. In ATRP, the catalyst governs the equilibrium between propagating radicals and dormant species, thus affecting the polymerization control for a range of monomers and transferable atoms employed in the process. The design and the use of highly active catalysts could diminish the amount of transition metal complexes, extend ATRP to less active monomers and give access to new chain‐end functionalities. At the same time, very active catalysts can be involved in formation of organometallic species. Herein, the role of the catalyst on the ATRP equilibrium is carefully elucidated, together with recent observations on the impact of the catalyst nature on formation of organometallic species and relevant side reactions. Based on this knowledge, a perspective on the benefits and challenges that derive from the use of highly active ATRP catalysts is presented.

p‐Substituted Tris(2‐pyridylmethyl)amines as Ligands for Highly Active ATRP Catalysts: Facile Synthesis and Characterization

“…This relationship can be explained considering that 1) al inear relation exists between E A of [Cu II (L)Br] + ,thus its K ATRP and the values of s p and N of the substituents;a nd 2) changes in K ATRP are primarily dictated by the ability of the catalyst to activate the initiator/dormant chains,w hereas the deactivation reaction is less affected by the catalyst nature. [11] In CH 3 CN with EBiB,t he activity of Cu/TPMA PIP ,C u/ TPMA NMe2 ,and Cu/TPMA PYR was very similar (k act = 1.5-2 10 7 m À1 s À1 ). Overall, the simple two-step divergent synthetic approach proposed herein effectively yielded novel ATRP catalysts with comparable or even higher activity to the most active known ATRP catalyst.…”

“…[8a,10] Theb enefits of Cu/L complexes with high K ATRP are numerous. [11] First, high K ATRP results in alarger fraction of [Cu II (L)X] + deactivator relative to [Cu I (L)] + ,t hus enhancing the deactivation step and improving the polymerization control. Indeed, the polymer dispersity ()decreases with increasing the concentration of [Cu II (L)X] + .…”

“…[13a] Thus,d eveloping new catalysts with higher activity and comparable or better selectivity than existing catalysts is key to wellcontrolled low ppm ATRP.O ptimal ATRP catalysts exhibit not only rapid activation of ATRP initiators/dormant chains but also rapid deactivation of the propagating radicals to obtain well-controlled polymerizations. [11] Since the discovery of ATRP in 1995, various catalysts have been developed targeting not only higher activity,b ut also enhanced robustness,l ow cost, and facile synthetic procedures. [8a] 2,2'-Bipyridine (bpy) was the first ligand used in ATRP;t hen, its structure was modified by introducing different substituents in the para position (p)t ot he Cucoordinating nitrogen atoms ( Figure 1).…”

Fully oxygen-tolerant atom transfer radical polymerization triggered by sodium pyruvate

“…8 The most active copper catalysts with highly negative redox potentials allow a well-controlled polymerization at a loading of only 10 ppm relative to the monomer. [9][10][11][12] Even trace amounts of oxygen can inhibit polymerization by rapidly oxidizing the activator form of the catalyst Cu I /L to the inactive Cu II /L complex. 13 Furthermore, oxygen molecules can react with the propagating carbon-based radicals, thus terminating the polymerization process.…”

Iron Catalysts in Atom Transfer Radical Polymerization

“…ATRP catalysis has advanced based on developing new catalytic systems with the aim of progressively increasing the activity, efficiency, and selectivity of catalysts through designing ligands, using external stimuli to control the catalytic process, and also decreasing the amount of catalysts needed for achieving a controlled polymerization [11,12]. For instance, the L/Cu I activator for ATRP can be generated in situ via reduction of air stable L/Cu II -X using external stimuli.…”