title: Elucidation of a side reaction occurring during nitroxide-mediated polymerization of cyclic ketene acetals by tandem mass spectrometric end-group analysis of aliphatic polyesters.
abstract: BACKGROUND
  In order to prevent side reactions while developing new polymerization processes, their mechanism has to be understood and one first key insight is the structure of the end-groups in polymeric by-products. The synthetic method scrutinized here is the nitroxide-mediated polymerization (NMP) of a cyclic ketene acetal, a promising alternative process to the production of polyesters.
  
  
  METHODS
  Polymer end-group characterization was performed by mass spectrometry (MS), combining elemental composition information derived from accurate mass data in the MS mode with fragmentation features recorded in the MS/MS mode. Electrospray was used as the ionization method to ensure the integrity of original chain terminations and a quadrupole time-of-flight (QTOF) instrument was employed for high-resolution mass measurements in both MS and tandem mass spectrometry (MS/MS) modes.
  
  
  RESULTS
  Occurrence of side reactions in the studied polymerization method, first evidenced by an unusual increase in dispersity with conversion, was confirmed in MS with the detection of two polymeric impurities in addition to the expected species. Fragmentation rules were first established for this new polyester family in order to derive useful structural information from MS/MS data. In addition to a usual NMP by-product, the initiating group of the second polymeric impurities revealed the degradation of the nitroxide moiety.
  
  
  CONCLUSIONS
  Unambiguous MS/MS identification of end-groups in by-products sampled from the polymerization medium allowed an unusual side reaction to be identified during the NMP preparation of polyesters. On-going optimization of the polymerization method aims at preventing this undesired process.
authors.affiliation: Aix-Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
authors.forename: Bruna de Fátima
authors.initials: Bde F
authors.lastname: Albergaria Pereira
authors.affiliation: Aix-Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
authors.forename: Antoine
authors.initials: A
authors.lastname: Tardy
authors.affiliation: Aix-Marseille Université, CNRS, FR 1739, Fédération des Sciences Chimiques de Marseille, Spectropôle, Marseille, France.
authors.forename: Valérie
authors.initials: V
authors.lastname: Monnier
authors.affiliation: Aix-Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
authors.forename: Yohann
authors.initials: Y
authors.lastname: Guillaneuf
authors.affiliation: Aix-Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
authors.forename: Didier
authors.initials: D
authors.lastname: Gigmes
authors.affiliation: Aix-Marseille Université, CNRS, UMR 7273, Institut de Chimie Radicalaire, Marseille, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Charles