Determination of solubility parameters for poly(3-hydroxyalkanoates).

The three dimensional solubility parameters defined by Hansen are based on dispersion forces between structural units, interaction between polar groups and hydrogen bonding. For polar polymers such as poly(3-hydroxyalkanoates), P(3HA), this approach was used to obtain the three coordinates of a solubility parameter in terms of: a dispersion part, a polar part and a hydrogen bonding part. Thirty-eight different solvents for poly(3-hydroxybutyrate), PHB, which are mentioned in the literature are examined by this method and the theoretical predictions are compared with the experimental reports. Another overall comparison between PHA polymers provides their Hansen and Hildebrand parameters for side chain lengths up to C13. In this series a linear progression in calculated solubility parameters with side chain length was found. An Appendix provides information and data on calculation of the solubility parameters. While the solubility information is limited and only covers homopolymers, it should help to highlight some of the contradictions regarding PHB solubility. This semi-empirical approach is only valid for amorphous polymers hence crystallinity effects, which are important with PHB, as well as molecular weight effects still require analysis.