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.