Block microstructural characterization of copolymers formed from fluorinated and non-fluorinated alkyl polyisocyanates using desorption chemical ionization mass spectrometry

Guodong Chen, R. Graham Cooks, Salil K. Jha, David Oupicky', Mark M. Green

Research output: Contribution to journalArticle

8 Scopus citations

Abstract

Homopolymers and copolymers of 1-isocyanato-4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluorononane (monomer F) and n-hexylisocyanate (monomer H) were examined by desorption chemical ionization mass spectrometry (DCI-MS) to obtain information on the monomer distribution in the copolymers. Tandem mass spectrometry (MS/MS) was used to characterize ions generated by DCI in the mass spectrometer ion source; ammonia and isobutane were selected as chemical ionization (CI) reagent gases. The major peaks in the ammonia DCI mass spectrum of poly(4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluorononyl)isocyanate (poly (F)) are protonated and ammoniated trimers. This result suggests that on pyrolytic degradation poly (F) forms cyclic trimers as do alkyl isocyanate polymers. The isobutane DCI mass spectra display the characteristic alkene elimination sequence characteristic of poly(n-hexyl)isocyanate and poly(2,6-dimethylheptyl)isocyanate but with additional extensive fragmentation. The major fragment ion is the protonated monomer. The monomer distributions in copolymers comprised of monomer F and monomer H were deduced from the abundances of various protonated and ammoniated trimers in the ammonia DCI mass spectra using Markovian statistics. Both soluble and insoluble copolymer samples were isolated and found to have non-random monomer distributions. The soluble fraction is dominated by monomer H blocks while the insoluble fraction also contains a majority of monomer H blocks but relatively more monomer F blocks. This forms an example in the polyisocyanates, which hitherto exhibited only random copolymerization, of a non-living method of polymerization yielding a block microstructure for a mixture of two monomers with virtually identical polymerizable functions. Mass spectrometry offers information on chain microstructure which would be unavailable by other means.

Original languageEnglish (US)
Pages (from-to)391-404
Number of pages14
JournalInternational Journal of Mass Spectrometry and Ion Processes
Volume165-166
DOIs
StatePublished - 1997
Externally publishedYes

Keywords

  • DCI/MS
  • Fluorinated polymer
  • Helical copolymer
  • MS/MS
  • Pyrolysis

ASJC Scopus subject areas

  • Spectroscopy

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