TIME-OF-FLIGHT SECONDARY-ION MASS-SPECTROMETRIC ANALYSIS OF POLYMER SURFACES AND ADDITIVES

This paper presents the application of static time-of-flight secondary ion mass spectrometry (ToF-SIMS) to the analysis of polymeric materials, including chemically modified polymers and polymer additives. Through the detection of intact functionalized oligomers, analysis of poly(styrene) functionalized with perfluoroalkyl chlorosilane provides confirmation of a successful endgroup termination for a living polymerization. The calculated molecular weight distribution also is in good agreement with chromatographic results. High mass resolution studies allow monitoring of the hydrogenation of a poly(butadiene) polymer through increases in oligomer mass due to proton addition. The quantitative ToF-SIMS results for the extent of hydrogenation for a specific oligomer are lower than the values averaged over all oligomers as determined by magnetic resonance. The usefulness of ToF-SIMS for determination of trace-level polymer additives is demonstrated for linear low-density poly(ethylene) (LLDPE). Application of a 150 nm thick evaporated Ag pattern enables in situ detection of the five trace additives present in the LLDPE matrix, and also provides information on additive surface migration and surface oxidation. A study of the silver cationization process for the silver-patterned LLDPE surface suggests differences in diffusion and/or ionization processes for two additives. This is confirmed with mass-resolved ion imaging to show the lateral distribution of the silver-cationized signals for various polymer additive molecular ions. Finally, poly(styrene) (M(n) = 1300) coated with a continuous silver overlayer is investigated. The ToF-SIMS-determined molecular weight distribution shifts to lower masses, suggesting the greater diffusion of shorter polymer chains through the silver overlayer.