Polyferrocenylsilanes as Protective Charge Migration Coatings for Dielectrics

Polyferrocenylsilanes [Fe(η-C₅H₄)₂SiMePh] _n (3) and [Fe(η-C₅H₄)₂SiMe₂] _n (4) were prepared by transition metal-catalyzed ring-opening polymerization (ROP) and thin films of these materials were studied to investigate their potential utility as protective charge migration coatings for dielectrics. Films ( 15 μm) of 3 or 4 cast from a concentrated toluene solution coated on Mylar did not experience any arc discharging when exposed to a beam of low energy (20 keV) electrons for a 1 h time period. In order to further investigate the charge migration properties of polyferrocenylsilanes, thick shapes and films of 3 were prepared by mold-extrusion and solution-casting onto a Teflon substrate, respectively. Charge accumulation measurements on 3 using a nonintrusive electrostatic probe showed that even after a 1 h exposure to a 25 keV electron flux, no appreciable charge accumulation existed. The direction of current flow was explored by constructing a device consisting of a film (thickness ca. 100–130 μm) of polymer 3 coating a layer of copper. When positioned beneath a circular mask and exposed to a low energy electron flux (5–25 keV), measurements of the current at the surface of the polymer film either exposed to or not exposed to the electron flux were not significantly different, and the current recorded from the bare copper connection to the ground was significantly (100–1000 times) higher. Although the mechanism of charge migration in polyferrocenylsilanes is not fully understood, these experiments indicated it may arise from a conduction mechanism, however electron scattering may also be involved.Dedicated to Professor Richard J. Puddephatt in recognition of his outstanding and scholarly contributions to chemistry.