A Versatile Method of Initiator Fixation for Surface-Initiated Living Radical Polymerization on Polymeric Substrates

Abstract

A facile yet robust approach to chemically fix an initiating group for atom transfer radical polymerization (ATRP) on various polymeric substrates is described. Conventional free radical copolymerization was conducted with methyl methacrylate (MMA), 2-(2-bromoisobutyryloxy)ethyl methacrylate (an ATRP initiator-carrying monomer, BIEM), and 2-((4-azidobenzoyl)oxy)ethyl methacrylate (a photoreactive phenylazide-carrying monomer, ABEM) in N,N-dimethylformamide at 75 °C, giving a random (statistical) copolymer. Thin films of the obtained copolymer were fabricated on poly(ethylene terephthalate) (PET) film surface by spin-casting a toluene solution of the terpolymer and were immobilized on the PET substrate via UV-irradiation using the photoreactivity of the phenylazido units. The surface-initiated ATRP (SI-ATRP) of poly(ethylene glycol) methacrylate (PEGMA) mediated by a copper complex was carried out in water at 30 °C in the presence of a sacrificial (free) initiator and the initiator-immobilized PET film as the solid substrate. The polymerization proceeded in a living fashion. The molecular weight of free polymer increased with polymerization time while retaining low-polydispersity index, and more importantly, the thickness of the poly(PEGMA) graft layer increased as a function of polymerization time with a reduced graft density (surface occupancy) as high as 0.5 in all examined time. This initiator immobilization technique was applied to various polymeric substrates including polystyrene, polypropylene, polyethylene, and polylactide. The fabrication of micropatterned polymer-brush surfaces was also demonstrated by photopatterning the initiator layer followed by SI-ATRP.