No 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.

The synthesis of ultrathick concentrated poly-(methyl methacrylate) (PMMA) brushes by atom transfer radical polymerization (ATRP) was investigated. The reactions were performed with a catalyst system of Cu(I)Br/dinonyl-2,2′bipyridine (dN-bipy) and Cu(II)Br 2 /dN-bipy at 60 °C under a high pressure of 500 MPa. The equilibrium constant for this catalyst system was determined to be 1.5 × 10 −6 , which followed the kinetics study and indicated good polymerization rate control. Under the high pressure of 500 MPa, a micrometer scale thick PMMA brush was obtained. During chain growth under the high pressure, the concentration of the deactivator catalyst was demonstrated to significantly affect the graft density of PMMA brushes, which was correlated to the number of monomers added in activation−deactivation cycles. A novel "cutoff" experiment and gel permeation chromatography demonstrated similar propagation for free polymers and graft polymers even under high pressure.