Structure and reaction mechanism for the monoacid diol polyester from caprolactone and 2,2′-bis(hydroxymethyl)propionic acid: NMR and melting-point evidence

The product distribution in the synthesis of acidic hydroxypolyesters from a 6/1 mol ratio of caprolactone and 2,2′‐bis(hydroxymethyl)propionic acid (DMPA) changes with reaction time and temperature. 13C‐nuclear magnetic resonance (NMR) signals were identified that are specific for all the possible substitution products around the quaternary carbon in the DMPA. This allows quantitative determination of the six different species that are present. NMR studies showed that over one‐half of the product is substituted on only one of the DMPA hydroxyls. The residual DMPA concentration increases at times and temperatures higher than those required to just complete caprolactone conversion because of equilibration of the kinetic product. All process conditions produced polyesters with two melting points. This suggests that the monosubstituted and disubstituted families of oligomers which are present are not completely miscible with one another. Polyester melting points increase as reaction time and temperature increase. This indicates that the degree of polymerization of the polycaprolactone arms increases as the severity of the preparative condition increases. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2217–2226, 2001