Characterization of linear and branched polyacrylates by tandem mass spectrometry

Kittisak Chaicharoen, Michael J. Polce, Anirudha Singh, Coleen Pugh, Chrys Wesdemiotis

Research output: Contribution to journalArticle

Abstract

The unimolecular degradation of alkali-metal cationized polyacrylates with the repeat unit CH2CH(COOR) and a variety of ester pendants has been examined by tandem mass spectrometry. The fragmentation patterns resulting from collisionally activated dissociation depend sensitively on the size of the ester alkyl substituent (R). With small alkyl groups, as in poly(methyl acrylate), lithiated or sodiated oligomers (M) decompose via free-radical chemistry, initiated by random homolytic C-C bond cleavages along the polymer chain. The radical ions formed this way dissociate further by backbiting rearrangements and β scissions to yield a distribution of terminal fragments with one of the original end groups and internal fragments with 2-3 repeat units. If the ester alkyl group bears three or more carbon atoms, cleavages within the ester moieties become the predominant decomposition channel. This distinct reactivity is observed if R∈=∈t-butyl, n-butyl, or the mesogenic group (CH 2)11-O-C6H4-C6H 4-CN. The [M+alkali metal]+ ions of the latter polyacrylates dissociate largely by charge-remote 1,5-H rearrangements that convert COOR to COOH groups by expulsion of 1-alkenes. The acid groups may displace an alcohol unit from a neighboring ester pendant to form a cyclic anhydride, unless hindered by steric effects. Using atom transfer radical polymerization, hyperbranched polyacrylates were prepared carrying ester groups both within and between the branches. Unique alkenes and alcohols are cleaved from ester groups at the branching points, enabling determination of the branching architecture. [Figure not available: see fulltext.]

Original languageEnglish (US)
Pages (from-to)595-607
Number of pages13
JournalAnalytical and Bioanalytical Chemistry
Volume392
Issue number4
DOIs
StatePublished - Oct 2008
Externally publishedYes

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Keywords

  • Branching architecture
  • Charge-remote rearrangement
  • Degradation mechanisms
  • Hyperbranched polyacrylates
  • Mesogenic substituents
  • Polyacrylate fragmentation
  • Tandem mass spectrometry

ASJC Scopus subject areas

  • Analytical Chemistry
  • Biochemistry

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