Macromolecular Stereochemistry: Effect of Pendant Group Structure on the Conformational Properties of Polyisocyanides1,2

Mark M. Green, Richard A. Gross, Frederic C. Schilling, Karl Zero, Charles Crosby

Research output: Contribution to journalArticle

Abstract

The hydroxyl function of the S enantiomer of the 1,2-acetone ketal of propylene glycol wasconverted, via the amine, to the isocyanide ([α]646+32.9° (CHC13)), which was polymerized by using NiCl2hexahydrate in the neat state to the derived poly((S)-2,2-dimethyl-l,3-dioxolane-4-methyl isocyanide) ([α]S46+68.5° (p-dioxane); Mw= 165000). The ultraviolet spectrum of this brown solid in CHC13exhibited a band, as a shoulder on lower wavelength absorptions, with λmax= 295 nm and 3.2 X 102 L mor1 cm-1, and a long low-intensity visible region tail. The circular dichroism (CD) spectrum was similar to published spectra for α-substituted asymmetricpolyisocyanides and showed three maxima (λmax>nm; Δe, L mol-1 cm-1): 328, -0.082; 290, +0.015; 275, -0.047. High-field 13C NMR studies exhibited extensive chemical shiftdispersion for both the backbone carbon and the pendant carbons. Similar shift dispersion was encountered in poly(n-butyl isocyanide) and in poly(benzyl isocyanide). Poly((R)-α-phenylethyl isocyanide) also exhibited chemical shift dispersion superimposed on symmetrical but broadened lines in its 13C NMR spectrum. Zimm plots constructed fromwide-angle 633-nm light scattering data on poly((#)-a-phenylethyl isocyanide) (Mw= 107 000) and on poly((iS)-2,2-dimethyl-l,3-dioxolane-4-methyl isocyanide) (Mw= 165000) showed no angular dependence. The weight average hydrodynamic radii of thesepolymers in tetrahydrofuran were determined by photon correlation spectroscopy to be 51 and 24 Å, respectively. If one adopts a 4/1 helix with a pitch of 4 Å proposedin the literature for poly(a-phenylethyl isocyanide), our data yield a persistence length of 32 Å, which is substantially largerthan that for poly(S)-2,2-dimethyl-l,3-dioxolane-4-methyl isocyanide). The results show that some form of stereoirregularity, which could involve syn-antiisomerism about the carbon-nitrogen double bond, is seen in each of thepolymers studied. In addition, the chain dimension is strongly dependent on the pendant group structure.

Original languageEnglish (US)
Pages (from-to)1839-1846
Number of pages8
JournalMacromolecules
Volume21
Issue number6
DOIs
StatePublished - 1988

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

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