SPECTROSCOPIC EVIDENCE FOR RADIATION-INDUCED CROSS-LINKING OF POLY(TETRAFLUOROETHYLENE)

Direct spectroscopic evidence for radiation-induced crosslinking of poly (tetrafluoroethylene) (PTFE) is presented for all x-ray and electron dose levels above which it is possible to distinguish between deliberately introduced radiation damage and the x-ray damage inherent in obtaining an x-ray photoelectron spectrum (XPS). The C (1s) spectrum obtained after irradiation with 2 keV electrons for all doses greater than 1 muA-min/cm2 consists of a four-peak spectrum identical to that previously obtained for plasma-polymerized tetrafluoroethylene and assigned to carbon atoms with variable numbers of bound F atoms (CF3, CF2, CF1, and CF0). X-ray irradiated PTFE can be fitted with the same four-peak spectrum. At or below an electron dose level of 1 muA-min/cm2, the radiation damage is comparable to that produced by the x-ray dose necessary to obtain an XPS spectrum. The CF1 and CF0 components increase with increasing electron dose, and at high electron doses dominate the spectrum. With increasing dose the CF3 component approaches a constant value while both the CF2 component and the total F : C ratio decreases. These four components are those expected to result from radiation-induced crosslinking reactions of the polymer and are consistent with previous suggestions that crosslinking is the basis of radiation patterned adhesion to PTFE.