Miniemulsion ARGET ATRP via Interfacial and Ion-Pair Catalysis: From ppm to ppb of Residual Copper

It was recently reported that copper catalysts used in atom transfer radical polymerization (ATRP) can combine with anionic surfactants used in emulsion polymerization to form ion pairs. The ion pairs predominately reside at the surface of the monomer droplets, but they can also migrate inside the droplets and induce a controlled polymerization. This concept was applied to activator regenerated by electron transfer (ARGET) ATRP, with ascorbic acid as reducing agent. ATRP of <i>n</i>-butyl acrylate (BA) and <i>n</i>-butyl methacrylate (BMA) was carried out in miniemulsion using Cu^II/tris­(2-pyridylmethyl)­amine (TPMA) as catalyst, with several anionic surfactants forming the reactive ion-pair complexes. The amount and structure of surfactant controlled both the polymerization rate and the final particle size. Well-controlled polymers were prepared with catalyst loadings as low as 50 ppm, leaving only 300 ppb of Cu in the precipitated polymer. Efficient chain extension of a poly­(BMA)-Br macroinitiator confirmed high retention of chain-end functionality. This procedure was exploited to prepare polymers with complex architectures such as block copolymers, star polymers, and molecular brushes

Harnessing the Interaction between Surfactant and Hydrophilic Catalyst To Control <i>e</i>ATRP in Miniemulsion

Harnessing the Interaction between Surfactant and Hydrophilic Catalyst To Control <i>e</i>ATRP in Miniemulsio

Impact of Organometallic Intermediates on Copper-Catalyzed Atom Transfer Radical Polymerization

In atom transfer radical polymerization (ATRP), radicals (R^•) can react with Cu^I/L catalysts forming organometallic complexes, R–Cu^II/L (L = N-based ligand). R–Cu^II/L favors additional catalyzed radical termination (CRT) pathways, which should be understood and harnessed to tune the polymerization outcome. Therefore, the preparation of precise polymer architectures by ATRP depends on the stability and on the role of R–Cu^II/L intermediates. Herein, spectroscopic and electrochemical techniques were used to quantify the thermodynamic and kinetic parameters of the interactions between radicals and Cu catalysts. The effects of radical structure, catalyst structure and solvent nature were investigated. The stability of R–Cu^II/L depends on the radical-stabilizing group in the following order: cyano > ester > phenyl. Primary radicals form the most stable R–Cu^II/L species. Overall, the stability of R–Cu^II/L does not significantly depend on the electronic properties of the ligand, contrary to the ATRP activity. Under typical ATRP conditions, the R–Cu^II/L build-up and the CRT contribution may be suppressed by using more ATRP-active catalysts or solvents that promote a higher ATRP activity