XPS study on surface segregation in poly(ethylene-iso/terephthalate)-perfluoropolyether block copolymers

Samples of poly(ethylene-iso/terephthalate)-perfluoro polyether multiblock copolymers with perfluoropolyether (PFPE) segments of different lengths have been characterized for surface composition by XPS and angular dependent XPS in order to determine the influence of the length of the PFPE blocks on the surface segregation of fluorine moieties. The results indicated that there was a high surface excess of PFPE when the PFPE blocks had molecular weight (MW) of 2200; far a bulk content of PFPE of about 8%, the amount of PFPE at the surface was 94 wt %. When the MW of PFPE blocks was 3400 or 1200, for the same bulk content of PFPE of about 8%, the surface showed a more limited excess of PFPE (about 46 and 30 wt % for MW 3400 and 1200 respectively). The segregation capability of PFPE blocks was also influenced by the length of polyester segments to which the PFPE blocks are bonded. So, when the fraction of PFPE bonded to very short segments of polyesters was extracted, the surface enrichment was reduced, and for a bulk, composition of PFPE of about 6%, the surface amount of PFPE was of 15, 45, and 29% for PFPE with MW of 1200, 2200, and 3400, respectively. These data suggest that surface segregation depends on the MW of the initial PFPE and of the polyester segments bonded to PFPE after polymerization and that there is an optimum MW for PFPE surface segregation; the most favorable conditions are met for PFPE with MW 2200.