SURFACE STUDIES OF POLYPEPTIDIC BLOCK COPOLYMERS BY ELECTRON-SPECTROSCOPY FOR CHEMICAL-ANALYSIS - POLY(N-EPSILON-TRIFLUOROACETYL-L-LYSINE)-POLYSARCOSINE DIBLOCK COPOLYMERS

The surface of poly(N** epsilon -trifluoroacetyl-L-lysine)-polysarcosine (Kt. Sa) block copolymers was studied by electron spectroscopy for chemical analysis (e. s. c. a. ) on films cast from methanol. The e. s. c. a. results indicate that the copolymer composition of the surfaces (e. g. outermost approximately 35 A) may be significantly different from the overall bulk composition. A surface excess of Kt is observed for copolymers containing less than about 45 mol% Kt; the Kt excess increases as the bulk content of Kt decreases. Angular-dependent studies show that the concentration of Kt increases as the air-copolymer interface is approached. X-ray diffraction studies of the Kt. Sa copolymers in concentrated solution in methanol and in the dry state show that they exhibit a lamellar structure. Knowledge of this structure makes it easier to interpret the e. s. c. a. results. A model of the surface topography is proposed, namely that the lamellar structure is perpendicular to the air-polymer interface and the Kt domains are elevated above the Sa domains.