Mechanochemical ATRP: an asset for the bulk copolymerization of solid and liquid monomers

Atom Transfer Radical Polymerization (ATRP) is one breakthrough technique to obtain well-defined and controlled polymers or copolymers. However, this technique has been mainly considered in solution and alternatives such as solvent-free mechanochemistry in a ball-mill, an emerging approach for a greener and safer chemistry, is left aside as a tool for polymer synthesis. Nevertheless, mechanochemistry in a ball-mill offers many advantages and permits to avoid the use of solvent, with shorter reaction times and simplified treatment steps making it easier to recover the product of interest. Herein, interest was put onto the development of mechanochemical ARGET-ATRP conditions for styrene polymerization, one solid styrenic derivative sodium styrene sulfonate, one liquid styrenic derivative 4-vinylbenzyl chloride and a mixture of both monomers. A fine tuning of the catalyst quantity and easily removable ascorbic acid/Na2CO3 reducing agent, never describe in the ball-mill previously and more practical than other reducing agent, gave polymers and copolymers in good to excellent yield (up to >99 %), with a control over dispersity (typically Đ <1.5), as analyzed by 1H NMR and size exclusion chromatography, respectively. As a further matter, these unprecedented conditions allow to render null and void all considerations concerning the physical state, properties (hydrophilic, hydrophobic) and miscibility/solubility of monomers which are key parameters in solution based ATRP for the synthesis of polymer and copolymer.