Surface enrichment of siloxanes with covalent bound ultraviolet (UV) absorber groups

The ability of siloxanes with UV absorber groups to enrich at the surface of cast polystyrene films was studied. Model compounds were siloxanes of the type Me₃SiO(SiMe₂O)_n(SiMeRO)_mSiMe₃, withR representing a 2-hydroxy-benzophenone-4-oxypropyl group. Surface studies were carried out by contactangle measurements and ESCA (Electron Spectroscopy for Chemical Application) investigations. UV absorbers with a high content of dimethylsiloxane units strongly enrich at the surface of polystyrene, forming a thin surface layer with a high siloxane content. UV absorbers with few or no dimethylsiloxane units pe hydroxybenzophenone group are evenly distributed in the polymer matrix. ESCA sputter depth profiles are also given. Migration studies show that the siloxanes are delivered from the bulk to the surface subsequently after sputtering.Dedicated to Prof. Dr. Dr. h.c. R. Müller on the occasion of his 90th birthday, in recognition of his pioneering contributions to organosilicon chemistry.Siloxanes with Functional Groups, XIV. For communication XIII, see Ref. 1. Long-Term Stabilization of Polymers, VIII. For communication VII, see Ref. 1.