Macromolecular stereochemistry: an example of amplification via cooperation

Poly(n-alkyl isocyanates) have been shown to exist in dilute solution as stiff polymers with a stable helical conformation. The symmetry characteristics of these polymers allow an equal probability for the left (M) and right handed (P) helical senses and in polymers of high enough molecular weight it is expected that helix reversals could separate these regions. The stiff characteristics of poly(n-alkyl isocyanates) suggest helix reversals are rare and therefore that the amplification discussed should be large. Statistical thermodynamic calculations, Predict how the optical activity will depend on the degree of polymerization (N). At high values of N, [α] should be independent of N since helix reversals limit the cooperation while at low N the chain length limits cooperation and thus [α] will depend on N.