SURFACE MODIFICATION OF BISPHENOL-A-POLYCARBONATE BY FAR-UV RADIATION .2. IN AIR

Thin films of bisphenol-A-polycarbonate (PC) were exposed, in air, to far-UV radiation from a deuterium lamp (0.33 mW/cm2 at 180-240 nm, i.e. roughly twice the unshielded solar far-UV intensity). The PC surface was rapidly oxygenated (e.g. doubling of oxygen content in 1 h) and suffered considerable mass and thickness loss (about 10 nm/h), loss of carbonate functionality (initial quantum yield 0.094), and loss of phenylene functionality (initial quantum yield 0.030). The dominant photo-reactions were chain scissions, rather than the photo-Fries rearrangement, and the major volatile product was benzoic acid. After several hours irradiation, the quantum yields decreased considerably due to shielding by a layer of involatile oxidation products. In contrast to the vacuum irradiated case, the surface layer was not crosslinked, but rather suffered considerable photo-ablation, providing a possible route for photolithography. Far-UV modification is also relevant to the performance of PC in the low earth orbit (LEO) environment.