The Gas-Phase Reactivity of h⁵-cyclopentadienylcobalt ion (CpCo^.+) toward Saturated Hydrocarbons Using Fourier-transform Mass Spectrometry (FT-MS)

H.C. Michelle Byrd and Charles M. Guttman, Polymers Division, Standards and Data, Gaithersburg, MD  20899

Douglas P. Ridge, University of Delaware, Department of Chemistry and Biochemistry, Newark, DE 19716

By volume, polyethylenes, polypropylenes and their derivatives are the most widely used of all synthetic polymers. Their chemical structure and composition, molecular mass, and molecular-mass distribution (MMD) are critical in determining performance properties. The potential for quick and direct measurement of chemical composition and MMDs makes mass spectrometry especially attractive to the polymer industry. However, mass spectral analysis of saturated polyolefins has been plagued by the ineffectiveness of conventional methods of cationization due to the lack of polar groups, unsaturation and aromaticity. Selection of a suitable ionizing reagent is crucial for successful MS analysis.

The selective reactivity of the h⁵-cyclopentadienylcobalt ion (CpCo^.+) may provide a suitable cationization reagent for saturated hydrocarbons analysis by mass spectrometry. Therefore, the CpCo^.+ ion reactivity toward linear alkanes was examined in the gas-phase using FT-MS. Loss of two hydrogen molecules from the adduct ion was found to dominate all reactions ( > 80 %). Furthermore, the dehydrogenation reaction rate increases with increasing chain length, approaching the collision rate. These initial results suggest that the CpCo^.+ ion may be a promising cationization reagents of larger saturated polyethylenes.