We report the synthesis of polymeric C-Si films by electron or:ultraviolet photon bombardment of condensed vinyl silane derivatives. These films are resistant to thermal diffusion of Cu at temperatures below 800 K, even at thicknesses <100 Angstrom. They also show potential for providing a covalently bonded interphase between Cu and, e.g., fluoropolymer dielectrics. Auger data show that these films are not SiC, and have chemical compositions very close to those of the vinyl silane precursors [e.g., Si:C=1:4 for vinyltrichlorosilane (VTMS)-derived films]: Temperature programmed desorption results show that the polymerization occurs via the vinyl group. Films derived from VTMS are adherent and stable on Ta substrates until 1000 K in ultrahigh vacuum (UHV). Diffusion of Cu deposited overlayers is not observed below 800 K, with dewetting occurring only at temperatures above 400 K in UHV.. Perfluorobenzene moieties can also be incorporated into the growing him with good thermal stability, indicating that these films have the potential to adhesively couple Cu surfaces to vapor-deposited fluoropolymer films.