This paper is concerned with the e †ects that polymer molecular weight, casting solvent, soniÐcation (with a nonpolymer solvent) and annealing have upon the secondary ion mass spectrometry (SIMS) of polymers.
Films of a series of monodispersed poly(methyl methacrylate) (PMMA) standards, 2965-1 200 000, were M w prepared by solution casting from four solvents (tetrahydrofuran (THF), 2-butanone, toulene and chloroform) onto clean aluminium (Al) substrates. The PMMA Ðlms were characterized by high-and unit-mass resolution time-of-Ñight secondary ion mass spectrometry (ToF-SIMS). To determine the signiÐcance of variations seen in ion intensities, one PMMA sample was re-analysed 24 times, and the scatter in the absolute counts and normalized and ratioed ion intensities for speciÐc (termed "keyÏ) positive and negative ions were calculated. This provided 95% conÐdence error bars, which were subsequently employed. The 95% conÐdence limits were signiÐcantly reduced by normalizing or ratioing.
Molecular weight was found to have the greatest e †ect in the SIMS spectra obtained, with the di †erences being most marked between and This was seen in both the total negative ion counts (m/z M w = 2965 M w = 89 100. 31-200) and the key negative ion ratios. An explanation based on the surface concentration of chain ends is presented. Negative ion ratios were shown to be very sensitive to trace amounts of residual solvents. By annealing above the PMMA glass transition temperature solvent-free Ðlms were produced from three solvents and these T g were spectrally indistinguishable. Solvent-free Ðlms could not be produced from THF. Residual solvent was identi-Ðed by high mass resolution ToF-SIMS. SoniÐcation with hexane, a polymer non-solvent, had a considerable e †ect on the total negative ion counts (m/z 31-200). No concomitant chemical changes were detected, so this e †ect is thought to arise from a physical perturbation of the surface.
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