Molecular conformation of poly(S‐lactic acid)

Abstract

The predominant role of van der Waal interactions in determining the helical conformations of a simple synthetic linear polymer, as well as helical polypeptides, was pointed out in systematic studies by Liquori et al.1,2. In the case of homopolypeptides the conformational analysis carried out on the basis of a simple semiempirical function describing the van der Waal pairwise interactions between the non directly bonded atoms lead to the conclusion that only five helices are allowed (Rα, β, γ, δ, Lα).2,3 In view of the close similarities with poly‐L‐alanine, we have investigated by x‐ray and conformational analysis the molecular conformation of poly(S‐lactic acid) which has recently been described by Kleine and Kleine 4 and Schuls and Schwaab 5 and studied in solution by Goodman and D'Alagni.6 In fact, this polymer may be related to the polypeptide by the interchange of a peptide bond with ester bond along the main chain. This operation is expected to involve only a relatively small change in the steric interaction within the possible helical conformation, but obviously rules out any possibility of hydrogen bonding.