Photopolymerized Epoxide Copolymer Thin Films with Surfaces Highly Enriched with Sulfonyl Fluoride Groups

Abstract

Photoinitiated polymerization of fluorinated aliphatic epoxides bearing terminal sulfonyl fluoride groups with a commercial cycloaliphatic diepoxide (Cyracure UVR-6110) results in highly cross-linked glassy films. Depth-dependent surface analysis using XPS shows that these films are highly enriched in their outer molecular surface regions with sulfonyl fluoride groups. Films prepared with 17 wt % and higher sulfonyl fluoride epoxide monomers exhibit compositions close to that of a pure 100% photopolymerized sulfonyl fluoride epoxide monomer in the outer 50 Å of the film. Even a film prepared with 1 wt % sulfonyl fluoride monomer exhibits a few angstroms thick overlayer of sulfonyl fluoride. FTIR (attenuated total reflectance) spectra exhibit infrared signatures consistent with these data. Secondary ion mass spectra exhibit peaks associated with perfluoro and sulfonyl fluoride moieties, supporting overlayer enrichment of these species within the sampling depth of this method (outer 15 Å). Such extreme surface enrichment by the fluorinated epoxide has utility for applications where costly or exotic fluorinated monomers are required to impart a robust overlayer yet comprise only minority component additives of the total polymerization mixture.