Chiral optical properties of a helical polymer synthesized from nearly racemic chiral monomers highly diluted with achiral monomers

Salil K. Jha, Kap Soo Cheon, Mark M. Green, Jonathan V. Selinger

Research output: Contribution to journalArticle

Abstract

In polyisocyanates composed only of randomly distributed (R) and (S) units, the chiral optical properties of the polymer are far out of proportion to the enantiomeric excess of the monomers. This highly disproportionate relationship, which arises from a majority-rule effect among these enantiomeric units on the helical sense of the backbone, is now found to be unaffected, within certain limits, by the overwhelming presence of achiral units randomly distributed along the chain. This experimental result can be explained quantitatively by an analysis based on the one-dimensional random- field Ising model, which shows that dilution of the chiral units with achiral units increases the helical domain size in a manner that compensates for the dilution. In qualitative terms, since the random-field domain size is limited by the 'objection' of the minority units to the helical sense dictated by the majority units, dilution of this 'objection' acts to increase the domain size. As long as this domain size is not limited by the chain length or by thermal fluctuations, the achiral dilution will not reduce the optical activity of the polymer.

Original languageEnglish (US)
Pages (from-to)1665-1673
Number of pages9
JournalJournal of the American Chemical Society
Volume121
Issue number8
DOIs
StatePublished - Mar 3 1999

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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