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1. Mechanism of supplemental activator and reducing agent atom transfer radical polymerization mediated by inorganic sulfites: experimental measurements and kinetic simulations

   https://doi.org/10.1039/c7py01319a  

   Krys, Pawel; Fantin, Marco; Mendonça, Patrícia V.; Abreu, Carlos M.; Guliashvili, Tamaz; Rosa, Jaquelino; Santos, Lino O.; Serra, Arménio C.; Matyjaszewski, Krzysztof; Coelho, Jorge F. (January 2017, Polymer Chemistry)

   The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na 2 S 2 O 4 ), with Cu II Br 2 /Me 6 TREN as catalyst (Me 6 TREN: tris[2-(dimethylamino)ethyl]amine) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO 2 ˙ − radical anion derived from Na 2 S 2 O 4 , acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for Cu II /L to regenerate the main activator Cu I /L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu 0 . The electron transfer from SO 2 ˙ − , to either Cu II Br 2 /Me 6 TREN or R–Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of Cu II Br 2 /Me 6 TREN and solubility of Na 2 S 2 O 4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the Cu I /L complex, but markedly increased the reactivity of sulfites. 

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

   https://doi.org/10.1002/anie.202004724  

   Enciso, Alan E.; Lorandi, Francesca; Mehmood, Arshad; Fantin, Marco; Szczepaniak, Grzegorz; Janesko, Benjamin G.; Matyjaszewski, Krzysztof (June 2020, Angewandte Chemie International Edition)

   Abstract A facile and efficient two‐step synthesis ofp‐substituted tris(2‐pyridylmethyl)amine (TPMA) ligands to form Cu complexes with the highest activity to date in atom transfer radical polymerization (ATRP) is presented. In the divergent synthesis,p‐Cl substituents in tris(4‐chloro‐2‐pyridylmethyl)amine (TPMA^3Cl) were replaced in one step and high yield by electron‐donating cyclic amines (pyrrolidine (TPMA^PYR), piperidine (TPMA^PIP), and morpholine (TPMA^MOR)) by nucleophilic aromatic substitution. The [Cu^II(TPMA^NR2)Br]⁺complexes exhibited larger energy gaps between frontier molecular orbitals and >0.2 V more negative reduction potentials than [Cu^II(TPMA)Br]⁺, indicating >3 orders of magnitude higher ATRP activity. [Cu^I(TPMA^PYR)]⁺exhibited the highest reported activity for Br‐capped acrylate chain ends in DMF, and moderate activity toward C−F bonds at room temperature. ATRP ofn‐butyl acrylate using only 10–25 part per million loadings of [Cu^II(TPMA^NR2)Br]⁺exhibited excellent control. 

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3. Catalytic effect of DMSO in metal‐catalyzed radical polymerization mediated by disproportionation facilitates living and immortal radical polymerizations

   https://doi.org/10.1002/pol.20220632  

   Maurya, Devendra S.; Adamson, Jasper; Bensabeh, Nabil; Lligadas, Gerard; Percec, Virgil (February 2023, Journal of Polymer Science)

   Abstract DMSO, an interesting solvent for copper‐catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X₂. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex‐architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)‐wire‐catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2‐dimethylaminoethyl)amine, Me₆‐TREN, tris(2‐aminoethyl)amine, TREN, and Me₆‐TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration‐rate dependence was observed. The external order of reaction of the apparent rate constant of propagation,k_p^appon solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed. 

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4. Riboflavin‐Catalyzed Photoinduced Atom Transfer Radical Polymerization

   https://doi.org/10.1002/macp.202400323  

   Coskun, Halil Ibrahim; Votruba‐Drzal, Thomas; Wu, Hanshu; Jockusch, Steffen; Yilmaz, Gorkem; Matyjaszewski, Krzysztof (April 2025, Macromolecular Chemistry and Physics)

   Abstract The photoATRP of methyl acrylate (MA) is investigated using riboflavin (RF) and CuBr₂/Me₆TREN as a dual catalyst system under green LED irradiation (λ ≈ 525 nm). Both RF and CuBr₂/Me₆TREN enhanced oxygen tolerance, enabling effective ATRP in the presence of residual oxygen. High molar mass polymers (up toM_n ≈ 129 000 g·mol⁻¹) with low dispersity (Đ≤ 1.16) are prepared, and chain‐end fidelity is confirmed through successful chain extension. The molecular masses of the obtained polymer increased linearly with conversion and showed high initiation efficiency. Mechanistic studies by laser flash photolysis reveal that the predominant activator generation mechanism is reductive quenching of RF by Me₆TREN (83%, under [CuBr₂]/[Me₆TREN] = 1/3 condition), supported by polymerization kinetics and thermodynamic calculations. 

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5. A green solvent-to-polymer upgrading approach to water-soluble LCST poly( N -substituted lactamide acrylate)s

   https://doi.org/10.1039/D2GC02780A  

   Palà, Marc; El Khannaji, Hafssa; Garay-Sarmiento, Manuela; Ronda, Juan Carlos; Cádiz, Virginia; Galià, Marina; Percec, Virgil; Rodriguez-Emmenegger, César; Lligadas, Gerard (October 2022, Green Chemistry)

   We report a green solvent-to-polymer upgrading transformation of chemicals of the lactic acid portfolio into water-soluble lower critical solution temperature (LCST)-type acrylic polymers. Aqueous Cu(0)-mediated living radical polymerization (SET-LRP) was utilized for the rapid synthesis of N -substituted lactamide-type homo and random acrylic copolymers under mild conditions. A particularly unique aspect of this work is that the water-soluble monomers and the SET-LRP initiator used to produce the corresponding polymers were synthesized from biorenewable and non-toxic solvents, namely natural ethyl lactate and BASF's Agnique® AMD 3L ( N , N -dimethyl lactamide, DML). The pre-disproportionation of Cu( i )Br in the presence of tris[2-(dimethylamino)ethyl]amine (Me 6 TREN) in water generated nascent Cu(0) and Cu( ii ) complexes that facilitated the fast polymerization of N -tetrahydrofurfuryl lactamide and N , N -dimethyl lactamide acrylate monomers (THFLA and DMLA, respectively) up to near-quantitative conversion with excellent control over molecular weight (5000 < M n < 83 000) and dispersity (1.05 < Đ < 1.16). Interestingly, poly(THFLA) showed a degree of polymerization and concentration dependent LCST behavior, which can be fine-tuned ( T cp = 12–62 °C) through random copolymerization with the more hydrophilic DMLA monomer. Finally, covalent cross-linking of these polymers resulted in a new family of thermo-responsive hydrogels with excellent biocompatibility and tunable swelling and LCST transition. These illustrate the versatility of these neoteric green polymers in the preparation of smart and biocompatible soft materials. 

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