Epoxidation of surface-bound polynorbornene films on silicon: Preventing degradation via solvent effect

We describe a strategy to prevent the detachment of polymer chain during the epoxidation of covalently grafted polynorbornene (PNb) films. Surface-bound PNb was prepared by surface-initiated ring-opening metathesis polymerization (SIROMP) from Si/SiO2 substrates, and then epoxidized with meta-chloroperoxybenzoic acid by taking advantage of the double bonds along the polymer chains. The polymer-solvent interactions of three model solvents (dichloromethane, ether and methanol) with grafted PNb and grafted epoxidized PNb were studied by measuring the intrinsic viscosity of the free counterparts in solutions with a capillary viscometer. Oxidative degradation of the films was evaluated by ellipsometric thicknesses. The change in surface morphology was characterized with atomic force microscopy (AFM). Reactions of degradation and epoxidation of grafted PNb in three model solvents were studied. Kinetics study revealed that the surface-bound PNb is epoxidized gradiently from the surface toward the silicon substrate in ether. Through the solvent control, epoxidation of surface-bound PNb film without degradation was achieved under relatively mild condition.