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SYNOPSISIrradiation of polystyrene by 15 Mrad gamma or exposure to a 254 nm ultraviolet (UV) light source leads t o surface oxidation of the polymer to depths greater than 10 nm as opposed to -3 nm depth offered by either plasma or corona-discharge treatment. Oxidation increases linearly with UV irradiation time. More carboxyl (0 = C -0) acid functionality, which increases with depth, was detected for UV-treated polymer. With 3 Mrad gamma irradiation, only hydroxyl (C -0) groups were detected by XPS as the surface-oxidized species. ADXPS, GPC, and static SIMS data suggest that chain scission is the dominant degradation mechanism for polystyrene exposed to high gamma and UV radiation, respectively. 0 1993 John Wiley & Sons, Inc. INTRODUCTIONPolymer surfaces are modified to improve the surface properties such as surface energy and chemistry, while maintaining the bulk properties of the polymer. These properties are usually necessary to improve ( a ) adhesion, e.g., between fiberlresin interface; ( b ) biocompatibility; ( c ) printability; and ( d ) wettability of surfaces for tissue culture applications. The high-energy processes used for the modification of polymer surfaces include corona-discharge, lowpressure O2 plasma, and ultraviolet radiation.The reactions between a polymer surface and corona discharge are believed to proceed by a freeradical mechanism via a peroxide intermediate. oxides, carbonyls, epoxys, carboxylic acids, and esters. In applications such as label adhesion, cell adhesion, chemical coupling, etc., the extent of crosslinking or chain scission due to the treatment may be of equal importance to product performance as are the relative distribution and quantity of oxidized functional groups on the polymer surface. Failure to consider short-chain soluble species resulting perhaps from extensive chain scission could have adverse effects on the adhesion and/or mechanical properties ( e.g., hardness, tensile strength, fracture stress) of the surfaces. Therefore, it is important to evaluate the degree of cross-linking and/or chain scission due to the treatment of polymers by the various high-energy processes. Angle-dependent X-ray photoelectron spectroscopy ( ADXPS ) is a surface-sensitive technique for nondestructive depth profiles (< 10 nm thickness) of polymers. Therefore, ADXPS should be particularly sensitive to changes in the types, concentration, and depth distribution of the surface functional groups. Static secondary ion mass spectrometry (SIMS) can provide structural or long-range information about surface species; hence, it is complementary to XPS.In this work, ADXPS, size exclusion chromatography, formally known as gel permeation chromatography (GPC ), infrared spectroscopy, and static SIMS were used to study the effect of high energy 2187 2188 ONYIRIUKA ( corona-discharge, oxygen plasma, ultraviolet, Xray radiation, and gamma) treatments on polystyrene. EXPERIMENTAL Material TreatmentsThe surfaces studied were commercial injectionmolded polystyrene dishes and roller bottles (except film...

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The effect of gamma-radiation on the surface chemical properties of polystyrene was studied by ESCA and FT-IR. Gamma-radiation produces surface >C=O and C-O containing functional groups only, and also causes oxidation to depths >10 nm as detected by ESCA. FT-IR spectra showed that below the top few molecular layers ester, acid, and carbonyl groups of various types were present. The α,β-unsaturated carbonyl/acid groups form a higher proportion of the total carbonyls with increasing depth. Surface oxidation follows pseudo-first-order kinetics; the extent of interior oxidation is linear with dose.