AVS 46th International Symposium
    Applied Surface Science Division Monday Sessions
       Session AS1-MoA

Paper AS1-MoA9
Quantitative ToF-SIMS and XPS Studies of Surface Structures in Alkyl Side-Chain Polyetherurethanes

Monday, October 25, 1999, 4:40 pm, Room 610

Session: Molecular Mass Spectrometry including Interpretation
Presenter: S.C. Porter, University of Washington
Authors: S.C. Porter, University of Washington
D.G. Castner, University of Washington
B.D. Ratner, University of Washington
Correspondent: Click to Email
Surface enrichment of polyether soft segment (SS) is typical in segmented polyetherurethanes (PEUs). The incorporation of surface active side-chains (SC) into the relatively polar hard segment (HS) block of the polymer significantly alters the surface structure. PEUs having various lengths and densities of alkyl SCs were synthesized. XPS analysis showed that PEUs with long SCs had high surface concentrations of hydrocarbon (HC) chains. Similarly, HS blocks were drawn toward, and concentrated just below, the HC rich surface. Positive ToF-SIMS spectra of these polymers contained fragments unique to both the HS and SS of the PEUs. Numerous HC fragments from the set, (@super+@C@sub x@H@sub 2x+1@ and @super +@C@sub x@H@sub 2x-1@; x @<=@ 7), could be indirectly associated with the length and/or density of alkyl SCs. Negative spectra contained fragments unique to individual SC species and HS fragments analogous to those found in the positive spectra. Ion ratios were used to determine the HS/SS (pos. spectra) and SC/HS (neg. spectra) surface concentration ratios. The HS/SS and SC/HS ratios increased with both side-chain length and density. Comparison of log(HS/SS) to actual concentration ratios obtained from XPS data, yielded linear correlations. The correlations improved as the sampling depth of the XPS experiments approached that of SIMS. The presence of isomeric HS fragment pairs in both positive and negative SIMS spectra provided an intrinsic reference for direct comparisons of the intensity of the positive HC fragments with a negative SC fragment. An analytical relation based on theoretical ion intensities was established for a series of PEUs having the same SC. Ion ratios from the positive spectra and a ratio from the negative spectra were shown to be directly proportional. The proportionality constant was solely a function of the ionization probabilities for the various ions utilized. HC fragments which did not contain contributions from either the HS or SS showed good correlations with the SC fragment intensity.