Direct analysis in real time mass spectrometry (DART-MS) of highly non-polar low molecular weight polyisobutylenes

Low molecular weight polyisobutylenes (PIB) with chlorine, olefin and succinic acid end-groups were studied using direct analysis in real time mass spectrometry (DART-MS). To facilitate the adduct ion formation under DART conditions, NH₄ Cl as an auxiliary reagent was deposited onto the PIB surface. It was found that chlorinated adduct ions of olefin and chlorine telechelic PIBs, i.e. [M + Cl]^- up to m/z 1100, and the deprotonated polyisobutylene succinic acid [MH]^- were formed as observed in the negative ion mode. In the positive ion mode formation of [M + NH₄ ]⁺ , adduct ions were detected. In the tandem mass (MS/MS) spectra of [M + Cl]^- , product ions were absent, suggesting a simple dissociation of the precursor [M + Cl]^- into a Cl^- ion and a neutral M without fragmentation of the PIB backbones. However, structurally important product ions were produced from the corresponding [M + NH₄ ]⁺ ions, allowing us to obtain valuable information on the arm-length distributions of the PIBs containing aromatic initiator moiety. In addition, a model was developed to interpret the oligomer distributions and the number average molecular weights observed in DART-MS for PIBs and other polymers of low molecular weight. Copyright © 2015 John Wiley & Sons, Ltd.