Acute Degradation of Surface-Bound Unsaturated Polyolefins in Common Solvents under Ambient Conditions

Abstract

We describe the detachment of covalently grafted polybutadiene and polynorbornene chains, which were prepared by surface-initiated ring-opening metathesis polymerization (SiROMP), from Si/SiO2 substrates upon brief exposure to common solvents in air. Degradation and disappearance of grafted polybutadiene films after successive rinses with dichloromethane were monitored by ellipsometry. Changes in surface topography were analyzed by atomic force microscopy. The rapid auto-oxidation of allylic carbon−hydrogen bonds renders these thin films extremely susceptible to degradation under ambient conditions. Polymers in the tethered state suffer more acute degradation (on the time scale of seconds) compared to those dissolved in solution (not detectable after days). To prevent degradation, unsaturated polymers prepared by SiROMP and the subsequent conversion (of unsaturated groups) need to be carried out under inert atmosphere. For example, smooth polybutadiene thin films of ∼100 Å thickness were covalently attached to silicon substrates via SiROMP of cyclooctadiene in the vapor phase. Solvent rinsing to remove unreacted monomers and free oligomers/polymers was carried out prior to the conversion of double bonds to epoxide groups. When these steps were carried out under nitrogen, negligible film loss was observed, and surface topography of the thin films was preserved. Once the unsaturation was removed from polybutadiene, the epoxidized and hydroxylated polybutadiene films were stable toward solvent exposure in air