Aqueous SARA ATRP using inorganic sulfites

Abstract

Aqueous supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) using inorganic sulfites was successfully carried out for the first time. Under optimized conditions, a well-controlled poly[oligo(ethylene oxide) methyl ether acrylate] (POEOA) was obtained with <30 ppm of soluble copper catalyst using tris(2-pyridylmethyl)amine (TPMA) ligand in the presence of an excess of halide salts (e.g. NaCl). Inorganic sulfites (e.g. Na2S2O4) were continuously fed into the reaction mixture. The mechanistic studies proved that these salts can activate alkyl halides directly and regenerate the activator complex. The effects of the feeding rate of the SARA agent (inorganic sulfites), ligand and its concentration, halide salt and its concentration, sulfite used, and copper concentration, were systematically studied to afford fast polymerizations rates while maintaining the control over polymerization. The kinetic data showed linear first-order kinetics, linear evolution of molecular weights with conversion, and polymers with narrow molecular weight distributions (Đ ~1.2) during polymerization even at relatively high monomer conversions (~80%). “One-pot” chain extension and “one-pot” block copolymerization experiments proved the high chain-end functionality. The polymerization could be directly regulated by starting or stopping the continuous feeding of the SARA agent. Under biologically relevant conditions, the aqueous SARA ATRP using inorganic sulfites was used to synthesize a well-defined protein-polymer hybrid by grafting of P(OEOA480) from BSA-O-[iBBr]30.

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

“…The relevant reactions included in the model are based on previously reported experimental and simulation results. 14,21,26–28,33,38,39 Reactions include: dissolution and dissociation of the inorganic sulfite (1, 2); supplemental activation of (macro)alkyl halides by SO 2 •− (3, 4); reduction of X–Cu II /L and Cu II /L complexes by SO 2 •− (5, 6), ATRP equilibrium between (macro)alkyl halides and (macro)radicals (7, 8); halidophilicity equilibrium of Cu I /L and Cu II /L complexes (9, 10); addition of alkyl halide-derived radicals (R • ) to the monomer (11); propagation (12); termination of two R • radicals (13); termination of R • with a polymer radical ( ${\mathrm{normalP}}_{\mathrm{normaln}}^{•}$) (14) and termination of two ${\mathrm{normalP}}_{\mathrm{normaln}}^{•}$ radicals (15). Reaction rate coefficients were either quantified by isolating the respective reactions ( vide infra ) or based on results provided in previous literature reports.…”

“…14,26–33 This avoided the continuous generation of soluble Cu species introduced into the system by activation of alkyl halides by Cu 0 and by comproportionation, effectively retaining a reduced concentration of metal catalyst. 14 Control experiments revealed that Na 2 S 2 O 4 can indeed activate alkyl halides as well as reduce Cu II Br 2 /L deactivator complex, thus acting as a typical SARA agent, similar to Cu 0 14,33 . However, no detailed mechanistic investigations have been conducted to evaluate the relative contribution of the participating reactions during a SARA ATRP with inorganic sulfites.…”

Self‐degassing SARA ATRP mediated by Na2S2O4 with no external additives

“…Sodium dithionite (Na 2 S 2 O 4 ) is a well‐known reducing agent, which has been previously used by our group as SARA agent for the SARA ATRP of different monomers in both organic and aqueous media near room temperature conditions . This inexpensive inorganic salt is also known for its ability to scavenge oxygen molecules .…”

Biocompatible polymers via aqueous electrochemically mediated atom transfer radical polymerization

“…By adhering to these “rules,” well‐controlled polymerizations of various water‐soluble monomers have been reported via normal ATRP, and different ATRP techniques based on the regeneration of the Cu(I) activator . Indeed, radical termination in ATRP causes the accumulation of [XCu II L] + deactivators, ultimately leading to early halt of the polymerization.…”