From free radical to atom transfer radical polymerization of poly(ethylene oxide) macromonomers in nanostructured media

Abstract

Polymerization of bifunctional α,ω-methacryloyloxypoly(ethylene oxide) (PEO) macromonomers was performed in water (or in organic solvents) via free radical or Atom Transfer Radical Polymerization (ATRP). Rapid cross-linking was observed when the reaction was conducted at 60°C via classical free radical polymerization with potassium peroxodisulfate as initiator. ATRP also yielded hydrogels, but the system was much more complex. In both cases, the characteristics of the resulting hydrogels (amount of extractable material, equilibrium swelling degree and uniaxial compression modulus) were studied. They depend on several parameters (precursor molar mass, macromonomer concentration, polymerization time and nature of the initiating system). The hydrogels obtained by ATRP are characterized by higher amounts of extractable materials and exhibit rather poor mechanical properties. Regardless of the polymerization process (free radical or ATRP), far better results were obtained when the reaction was conducted in water. In fact, in aqueous media, the hydrophobic end-standing polymerizable methacrylic units of the macromonomers self-organize, after which gel formation takes place much more rapidly.