Lactone ring formation in poly(α‐hydroxyacrylic acid)

Lactone ring formation in poly(α‐hydroxyacrylic acid) (PHA) was investigated by means of ¹H and ¹³C NMR. The stereoregularity of PHA was estimated as syndio‐rich (ca. 86%) on the basis of methylene proton peak of the sodium salt, PHANa, in aqueous solution. On the other hand, analyses of the ¹³C NMR spectra obtained as a function of the degree of dissocation (α) suggested that the lactone ring is formed at every other residue at half dissociation (α = 0.5). This specific way of lactone formation supposed for PHA is discussed in relation to the critical change in the dissociation behavior of the polyacid which has been found at α = 0.5. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1400–1405, 2002