Epoxides as Reducing Agents for Low‐Catalyst‐Concentration Atom Transfer Radical Polymerization

Abstract

Activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) conditions utilizing a low concentration of catalyst are successfully applied for the preparation of well-defined poly(glycidyl methacrylate) without the addition of external reducing agents. The living character of polymerization is evidenced by successful chain extensions with methyl methacrylate and methyl acrylate, again, in the absence of additional reducing agents, yielding block copolymers. The epoxide groups in glycidyl methacrylate or the corresponding polymer can serve as an intrinsic reducing agent to continuously regenerate the Cu(I) -based ATRP activator from the Cu(II) halide complex present in the systems. The reactivity of various epoxides in the reduction of the Cu(II) Br2 complex of tris(2-pyridylmethyl)amine is compared.

An efficient, heterogeneous, reusable atom transfer radical polymerization catalyst

“…This possibility may be prevented by treatment of the catalyst with a reducing agent to regenerate it for further ATRPs. For example, light, or reducing agents such as tin 2‐ethylhexanoate, ascorbic acid, methylaluminoxane, alcohols, triphenylphosphine and epoxides react with the oxidatively stable Cu(II) complex and generate the activator. Reusing an identical catalyst for five successive trials resulted in approximately 50% conversion at each polymerization.…”

Synthesis of Star Polymers with Epoxide-Containing Highly Branched Cores by Low-Catalyst Concentration Atom Transfer Radical Polymerization and Post-Polymerization Modifications

“…It was recently demonstrated that epoxides can act as reducing agents in low-catalyst concentration ATRP reactions (Scheme 2) (50,57), and in the chain extension reactions reported here, the epoxides present in the macroinitiator served to regenerate the lower oxidation state metal complex (activator) via reduction of the higher oxidation state deactivator.…”

“…Linear polyGMA was synthesized using low-catalyst concentration ATRP without external reducing agent (DP n,targ = 200) as previously reported (50). Dried polyGMA (100 mg, 70.3 μmol epoxide groups) was weighed into a small test tube equipped with a magnetic stir bar and dissolved with 0.5 mL DMSO-d 6 .…”

Tris(2-pyridylmethyl)amine Based Ligands in Copper Catalyzed Atom Transfer Radical Addition (ATRA) and Polymerization (ATRP)

“…TPMA is a widely used ligand for copper catalyzed ATRP methods ranging from conventional ATRP (41,42,102) to improved protocols that require only ppm amounts of the catalyst (13,40,49,(55)(56)(57)(58)(103)(104)(105)(106). These enhanced synthetic procedures allow for the use of air stable Cu II complexes, often eliminating the need for deoxygenation, and rely on the continuous reduction of Cu II to Cu I species within the polymerization process.…”