Functionalization of cyclic olefin copolymer substrates with polyethylene glycol diacrylate for the in situ synthesis of immobilized nanoparticles

Nanoparticles as novel stationary phase could enhance chromatographic performance (efficiency and resolution). However, their implementation in columns is rather challenging. The methodological approach we propose is an in situ synthesis of such nanoparticles through photopolymerization of a miniemulsion containing hexyl acrylate monomers. While the miniemulsion composition was previously optimized, resulting in highly spherical monodisperse nanoparticles with a mean size inferior to 200 nm, the immobilization of such particles is not straightforward. The strategy consists in carrying out the miniemulsion polymerization in the very close vicinity of a reactive surface, namely cyclic olefin copolymer (COC), from which covalent bond can grow thanks to hydrogen abstraction. While the hydrophobic nature of COC appears to disturb the stability of the miniemulsion, a more polar surface allows simultaneous polymerization and anchoring of nanoparticles on the surface. Surface functionalization of COC with different monomers was tested in this work and polyethylene glycol dimethacrylate photografting was found to provide an adequate surface modification. It appears however that the extent of surface modification and especially the amount of initiator that is applied on the COC surface have consequences on both the spherical aspect and the number of resulting nanoparticles. An optimization of the PEGDA surface modification by central composite design in regards to PEGDA and BME amounts and irradiation time is proposed. SEM images after miniemulsion photopolymerization for different conditions of PEGDA photografting showed the impact of photografting on nanoparticle shape.