Styrene-butadiene copolymers were analyzed by static secondary ion mass spectrometry (S-SIMS) and laser ablation Fourier transform ion cyclotron resonance mass spectrometry (LA-FTICRMS) to obtain quantitative information based on specific ions. Silver deposition was performed on polystyrene, butadiene rubber and styrene-butadiene rubber. Under these experimental conditions, new secondary ions were detected, in particular silver-cationized butadiene [M(butadiene) - Ag](+) and styrene [M(styrene) - Ag](+) monomers. In contrast, LA-FTICRMS experiments did not require pretreatment. At high laser power density, UV photons (193, 266 and 355 nm) allowed the detection of styrene and butadiene monomers at m/z 104 and 54, respectively. The use of the observed ions by SIMS or LA-FTICRMS ensures that quantitative information on the relative distribution of each monomer is obtained. However, the silver coating thickness in the SIMS experiment seems to have an important influence on the quantitative information obtained. For LA-FTICRMS experiments, the best results are obtained at a wavelength of 355 nm.

ABSTRACT:The capabilities of ion bombardment and laser ablation coupled to mass spectrometry as independent techniques to investigate the surface thermooxidative stability of polystyrene, polybutadiene polymers, and styrene butadiene rubber (SBR) copolymers were investigated. Surface chemical modifications were detected according to the polymeric structure. The degradation products detected by static secondary ion mass spectrometry appeared at m/z 29, 43, and 55. Their compositions were related to the general formulae C n H m O ϩ with n ϭ 1-3 and m ϭ 1-3 for polybutadiene and styrene butadiene copolymers, whereas polystyrene was not affected by the aging treatment. The C n H m O ϩ ions result from butadiene unit degradation. The laser ablation ionization Fourier transform ion cyclotron resonance mass-spectrometry results confirmed the detection of C n H m O ϩ ions. Finally, it may be considered that the surface thermooxidative process of SBR copolymers begins with butadiene unit degradation. The development of butadiene unit oxidation showed a dynamic oxidation phase, which coincided with a loss of unsaturation. The influence of the polymer conformation (blocked, branched, and random) on the surface oxidation for 30% styrene SBR compounds was also studied.

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The formation of dimerized polystyrene molecules during static SIMS measurements, already reported in a previous paper [Surf. Interface Anal. 20, 549 (1993)l has been further investigated. Samples of styrene oligomers with very narrow molecular weight distribution were prepared by fractionating polystyrene standards by means of supercritical fluid chromatography and then irradiated in situ in a time-of-flight SIMS spectrometer. Pre-irradiated samples have also been studied for comparison purposes. The results obtained confirm that crosslinked (dimerized) species are formed and detected in the very low fluence range, and strongly support the hypothesis that, at least partly, the observation of this kind of ion beam modification is not due to ion impact overlaps during the measurement, but to primary modification/desorption events.