NEXAFS Spectromicroscopy of Polymers: Overview and Quantitative Analysis of Polyurethane Polymers

Stephen G. Urquhart^a, Adam P. Hitchcock^b, Archie P. Smith^a, Harald W. Adet^a,
Werner Lidyt^c, Ed G. Rightor^c and Gary E. Mitchell^c

a. Department of Physics, North Carolina State University, Raleigh, NC, 27695-8202, USA
b. Brockhouse Institute for Materials Research, McMaster University, Hamilton, ON, CANADA, L8S 4M1
c. Dow Chemical USA, Midland, MI, 48667 , USA

(Received 4 January 1999, accepted 19 April 1999)

Abstract
    The successful application of x-ray spectromicroscopy to chemical analysis of polymers is reviewed and a detailed application to quantitative analysis to polyurethanes is presented. Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy is the basis of chemical sensitive x-ray imaging, as well as qualitative and quantitative micro-spectroscopy. These capabilities are demonstrated by a review of recent work, and by presentation of new results outlining a methodology for quantitative speciation of polyurethane polymers. C 1s inner-shell excitation spectra of a series of molecular and polymeric model compounds, recorded by gas phase inelastic electron scattering (ISEELS) and solid phase NEXAFS techniques, are used to understand the spectroscopic basis for chemical analysis of polyurethanes. These model species contain the aromatic urea, aromatic urethane (carbamate) and aliphatic ether functionalities that are the main constituents of polyurethane polymers. Ab initio calculations of several of the model molecular compounds are used to support spectral assignments and give insight into the origin and relative intensities of characteristic spectral features. The model polymer spectra provide reference standards for qualitative identification and quantitative analysis of polyurethane polymers. The chemical compositions of three polyurethane test polymers with systematic variation in urea/urethane content are measured using the spectra of model toluene diisocyanate (TDI) urea, TDI-carbamate, and poly(propylene oxide) polymers  as reference standards.  @ 1999 Elsevier Science B.V. All rights reserved.