CHARACTERIZATION OF POLYURETHANE FORMULATIONS BY DIRECT PROBE ATMOSPHERIC PRESSURE CHEMICAL IONIZATION MASS SPECTROMETRY SARA E. WHITSON, ∗ CHRYS WESDEMIOTIS † DEPARTMENT OF CHEMISTRY ,THE UNIVERSITY OF AKRON,AKRON, OH 44325-3601 ROBERT P. LATTIMER LUBRIZOL ADVANCED MATERIALS,INC., 9911 BRECKSVILLE ROAD,CLEVELAND, OH 44141 ABSTRACT Complex, commercially available polyurethane polymers were heated at slowly increasing temperatures on a direct probe (DP) inserted into an atmospheric pressure chemical ionization (APCI) source of a quadrupole ion trap mass spectrometer. Slow heating of the probe allowed for temporal separation of the thermally desorbed components (such as additives) and thermal degradation products, based on their volatilities and bond stabilities. In situ analysis of the released desorption products and pyrolyzates was accomplished by APCI mass spectrometry. DP-APCI enabled the characterization of polyurethanes that cannot be analyzed directly by mass spectrometry. Distinctions could be made between polymer formulations with variable physical properties due to their different blends. INTRODUCTION The commercial applications of polyurethanes (PUs) are versatile and widespread; such polymers are used for the manufacture of foams, adhesives, sealants, elastomers, and a variety of medical and automotive devices. 1–3 PUs are generally synthesized from three components: a diisocyanate (OCN–R–NCO), a hydroxy-terminated polyether or polyester (HO–R ′ –OH), and a chain extender (usually a diol of small molecular weight, HO–R ′′ –OH), which react to yield a polymer with the general structure –O–R ′ –O–CO–NH–R–NH–CO–O–R ′′ –O–CO–NH–R–NH– CO–. 1 The diisocyanate and the chain extender form the “hard segments” and the polyol forms the “soft segments” of the PU. The chemical compositions and structures of R and R ′ , plus any additives used, control the physical properties of the resulting material and its ultimate use. 1–3 With the exception of low molecular weight PU prepolymers, 4, 5 commercial PUs are not amenable to mass spectrometry analysis 6 because they cannot be desorbed by matrix-assisted laser desorption ionization 7, 8 and/or are insoluble for electrospray ionization. 9 Qualitative iden- tification of the constituents of unknown PUs can, nevertheless, be achieved by mass spectral methods after prior thermal 10, 11 or chemical 12 degradation of the original product. In particular pyrolysis mass spectrometry is frequently employed to verify expected compositions, compare PUs from different batches, analyze unknown materials, and investigate materials with suspect appearance or properties. 10, 11 The thermal decomposition pathways of PUs have been studied extensively and are well understood. 13 The initial, low temperature (150–300 ◦ C) cleavage of the urethane bonds, viz. O–CO–NH, proceeds via three major pathways which involve (1) dissociation to yield an iso- cyanate and an alcohol, (2) dissociation to a primary amine, alkene, and carbon dioxide, and (3) elimination of carbon dioxide to form a secondary amine. 14–16 At higher temperatures, CO 2 elim- ination, secondary reactions, and degradation of the soft segments to cyclic oligomers become prominent. 17–19 Several papers have described the analysis of the thermal degradation products of PU samples by mass spectrometry. 10, 11,19–24 Two common experimental approaches involve off-line pyrolysis in a chamber external to the ion source of the mass spectrometer or pyrolysis inside the ion source through the use of a heated direct probe or pyrolysis probe. ∗ Current address: Case Western Reserve University, School of Medicine, Center for Proteomics and Bioinformatics, 10900 Euclid Ave., Cleveland, OH 44106-4988. † Corresponding author. Ph: 330-972-7699; email: wesdemiotis@uakron.edu 35