Dopant-Assisted Atmospheric Pressure Photoionization Mass Spectrometry of Polyisobutylene Derivatives Initiated by Mono- and Bifunctional Initiators

摘要

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.,CCl4)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(-)-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+COCl](+) adducts were observed for PIBs with an aromatic initiator moiety.The origin of the COCl+species is also discussed.(J Am Soc Mass Spectrom 2009,20,2342-2351)