Assemblies of Polyacrylonitrile-Derived Photoactive Polymers as Blue and Green Light Photo-Cocatalysts for Cu-Catalyzed ATRP in Water and Organic Solvents

Abstract

Photoluminescent nanosized quasi-spherical polymeric assemblies prepared by the hydrothermal reaction of polyacrylonitrile (PAN), ht-PLPPAN, were demonstrated to have the ability to photo-induce atom transfer radical polymerization (ATRP) catalyzed by low, parts per million concentrations of CuII complex with tris(2-pyridylmethyl)amine (TPMA). Such photo induced ATRP reactions of acrylate and methacrylate monomers were performed in water or organic solvents, using ht-PLPPAN as the photo-cocatalyst under blue or green light irradiation. Mechanistic studies indicate that ht-PLPPAN helps to sustain the polymerization by facilitating the activation of alkyl bromide species by two modes: 1) green or blue light-driven photoreduction of the CuII catalyst to the activating CuI form, and 2) direct activation of dormant alkyl bromide species which occurs only under blue light. The photoreduction of the CuII complex by ht-PLPPAN was confirmed by linear sweep voltammetry performed under illumination. Analysis of the polymerization kinetics in aqueous media indicated even though CuI complexes comprised only 1–1.4% of all Cu species at equilibrium, they exhibited high activation rate constant and activated the alkyl bromide initiators five to six orders of magnitude faster than ht-PLPPAN.

Open-air green-light-driven ATRP enabled by dual photoredox/copper catalysis

“…57 Dual catalytic ATRP systems use ppm-level copper catalysts to attain a controlled polymerization process in the ground state and photoredox catalysts (PCs) to reduce deactivators via photoinduced electron transfer, maintaining radical propagation. [58][59][60][61][62][63][64][65] Moreover, when a PC in the excited state has sufficient redox potential, it can react directly with a dormant C(sp 3 )-X polymer chain end, generating radicals and thus offering an additional activation pathway. These methods are highly efficient under long-wavelength light, but have limited oxygen tolerance.…”

Toward Green Atom Transfer Radical Polymerization: Current Status and Future Challenges

“…[265] Contrary to the oxidative quenching pathway where the excited photocatalyst directly activates RX, in the reductive quenching pathway PC* reacts with the electron donor, such as triethylamine or PMDETA, generating a radical anion (PC •− ) that activates RX. [153,266] 4.9.5. Enzymatic Catalysis Enzymes are nontoxic, naturally sourced and biodegradable; they work under mild conditions (below 100 °C), exhibit stereo-, regio-, and substrate selectivity, generally present a high catalytic turnover and can be easily removed from reaction products.…”

“…[ 265 ] Contrary to the oxidative quenching pathway where the excited photocatalyst directly activates RX, in the reductive quenching pathway PC* reacts with the electron donor, such as triethylamine or PMDETA, generating a radical anion (PC •− ) that activates RX. [ 153 , 266 ]…”

Fully Oxygen-Tolerant Visible-Light-Induced ATRP of Acrylates in Water: Toward Synthesis of Protein-Polymer Hybrids

“…Then, the generated activator Cu I /L reacts with a C­(sp 3 )–X polymer chain end to form a carbon radical and the X–Cu II /L deactivator. Oxygen tolerance in this approach can be achieved using an excess ligand. − However, photoinduced Cu-catalyzed ATRP typically requires the use of biocidal UV light. ,, In organocatalyzed ATRP (O-ATRP), the dormant polymer chain is directly activated by electron transfer from a photoredox catalyst (PC) in the excited state (Figure b). − O-ATRP is compatible with a wide range of visible light but is mainly limited to methacrylates and organic solvents. − ATRP with dual catalysis uses copper complexes to attain a controlled radical propagation and PCs to trigger and drive polymerization (Figure c). ,− The photoredox/copper dual catalysis overcomes the challenges of using biocidal UV light, poor oxygen tolerance, and limited monomer scope.…”