Surface Reduction of Poly(aryl ether ether ketone) Film: UV Spectrophotometric, 3H Radiochemical, and X-ray Photoelectron Spectroscopic Assays of the Hydroxyl Functions

The surface reduction of amorphous poly(aryl ether ether ketone) (PEEK) film was successfully achieved by wet chemistry using a solution of NaBH 4 in DMSO at 120 °C for 3 h. The resulting PEEK-OH film was fully characterized by MIR, UV−visible, and 1 H NMR spectroscopies; all the data were consistent with those of the references, 4-(4-methoxyphenoxy)benzhydrol and bulk-reduced PEEK (“PEEK-OH”). The surface of PEEK-OH film was analyzed by X-ray photoelectron spectroscopy (XPS). From the fine structures of the C1s and O1s peaks, we could determine a ratio of reduction reaching 75−85% of the monomer units contained in the 10 outermost atomic layers. The surface reactivity of the hydroxyl groups was assayed by derivatization with [ 3 H]acetic anhydride followed by liquid scintillation counting (LSC) of the sample-associated radioactivity. The PEEK-OH film was reacted with p -nitrophenyl chloroformate to furnish an activated surface (PEEK-OCO 2 PNP), the basic hydrolysis of which allowed the indirect spectrophotometric assay of the reactive OH groups. The PEEK-OCO 2 PNP film was further used to covalently fix amine derivatives via a carbamate linkage. Using [ 3 H]lysine and trifluoroethylamine, we were able to assay the surface reactivity by LSC and XPS respectively. The ratios of surface derivatization were within 5−30%. The PEEK-OH film was used as substrate for the cultivation of CaCo2 epithelial cells; the presence of surface hydroxyl functions moderately improves the polymer biocompatibility.