Nine polyisobutylene (PIB) derivatives with different end groups (chlorine, vinyl, isobutenyl, 2,2-diphenylvinyl, and carboxyl) and molecular weights (1000 to 4500 g/mol), initiated by monofunctional and aromatic bifunctional initiators were studied by atmospheric pressure photoionization mass spectrometry (APPI-MS) in both negative and positive ion modes. Consistent with previous findings, negative ion APPI-MS revealed end-group identities through the formation of PIB adducts with chloride ions formed in situ from a chlorinated solvent (e.g., CCl 4 ) in the presence of a dopant (toluene). In positive ion mode, considerable fragmentation of these PIB derivatives was observed, rendering end-group determinations very difficult. The M n values obtained by APPI(Ϫ)-MS were considerably lower than those determined by SEC for PIB derivatives with M n higher than 2000 g/mol. PIBs containing carboxyl termini can undergo collision-induced dissociation, yielding structurally important product ions. The resulting APPI-MS/MS intensities were found to reflect the "arm-length" distribution for PIBs with bifunctional aromatic moieties. In positive ion mode, [M ϩ COCl]

Abstract. Polyisobutylenes (PIBs) with different end-groups including chlorine, exoolefin, hydroxyl, and methyl prepared from aliphatic and aromatic initiators were studied by electrospray ionization mass spectrometry (ESI-MS). Independently of the end-groups, presence or absence of aromatic initiator moiety, these PIB derivatives were capable of forming adduct ions with NO 3 -and Cl -ions, thus allowing the direct characterization of these compounds in the negative ion mode of ESI-MS.