Synthesis and surface properties of fluorocarbon end-capped biodegradable polyesters

We report the synthesis and characterization of a new class of materials based on combining hydrolytically degradable polyesters and fluorocarbon surface chemistry. These materials have surface properties which overcome some of the limitations of polymeric materials in controlled cellular or tissue adhesion properties. Fluorocarbon chains of two lengths (CF3(CF2)(m)(CH2)n, where F7C1 and F10C2 represent m = 6 and n = 1 and m = 9 and n = 2, respectively) have been synthesized as the terminal end groups to L- and DL-polylactides (PLA) and poly(lactide-co-glycolide) copolymers. Using both ring-opening polymerization and the substitution of the fluorocarbon at terminal hydroxyl groups, polyesters with 1, 2, and 4 fluorocarbon end groups were obtained (F-polyesters). Angular dependent X-ray photoelectron spectroscopy (XPS or ESCA) revealed that end groups are segregated at the surface. Further, the results show their the surface coverage of fluorocarbon groups increases with increasing the concentration and the length of fluorocarbon end groups. The surface composition of F-polyesters can be controlled by blending these polymers with polyesters or by changing the architecture of fluorocarbon end groups. From ESCA data of F-polyesters after in-vitro hydrolysis at pH = 11.4, results from the F-polyester with a longer fluorocarbon end group (F10C2-) show that the surface erosion occurs at the topmost surface region during the initial hydrolysis period. The F-polyester having a short fluorocarbon group (F7C1-) shows a progressive decrease of surface fluorocarbon concentration as a function of hydrolysis time. This result is explained by a longer retardation time for water permeation into the sample bulk of F10C2-L-PLA due to greater segregation of fluorocarbon groups at the topmost; surface.