THERMAL RECONSTRUCTION OF SURFACE-FUNCTIONALIZED POLY(CHLOROTRIFLUOROETHYLENE)

The heterogeneous reaction of poly(chlorotrifluoroethylene) (PCTFE) film with lithium reagents in THF or heptane/THF solution results in a modification that introduces the alkyl group of the lithium reagent into the surface region of PCTFE. 2-(Lithiomethyl)-4, 4-dimethyloxazoline reacts to incorporate the trimethyloxazoline functionality in the outer 10-20 Å of the PCTFE film (PCTFE-TMO). Hydrolysis of PCTFETMO renders surface carboxylic acid groups (PCTFE-COOH). Hydroxyl groups are incorporated by reaction of PCTFE with 3-lithiopropyl ethyl acetal and subsequent hydrolysis (PCTFE-OH). The thickness of the modified layer in PCTFE-OH depends on the conditions of reaction; we have studied film samples with modified layers of ~30- and -1150- Å thickness. PCTFE-OH (30 Å) was further modified to yield PCTFE-OC(O)- CH3, PCTFE-0C(0)CF3, and PCTFE-OSiMe3. All of the surfaces are stable (give reproducible surface analytical data) indefinitely at room temperature. On heating for days at 80-110 °C the surface regions of PCTFE- TMO, PCTFE-OH(30 Å), PCTFE-OHU150 Å), PCTFE-COOH, and PCTFE-0C(0)CH3 reconstruct as evidenced by contact angle analysis. X-ray photoelectron spectroscopy (XPS) indicates the reconstruction of PCTFE-TMO and PCTFE-OH(30 Å), but little or no changes in XPS spectra occur on heating PCTFE- OHU150 Å), PCTFE-COOH, and PCTFE-0C(0)CH3. PCTFE-OC(O)CF3 and PCTFE-OSiMe3 show no tendency to reconstruct. A reconstruction process that involves the concomitant migration of modified repeat units from the outer 10 Å of the film sample to a deeper region and migration of unmodified PCTFE repeat units from a deeper region into the outermost 10 Å is evident in PCTFE-TMO and PCTFE-OH(30 Å). The distance scale of these motions is small; the majority of the modified repeat units remains in the outer 10 Å. Another reorganization process is evident from contact angle measurements of PCTFE-OC(O)CH3 and PCTFE- OH(1150 Å) and it involves motions of even smaller distance; repeat units do not measurably migrate (the composition of the outermost 10 Å remains constant) and we propose that they rotate. © 1990, American Chemical Society. All rights reserved.