Synthesis, Characterization, and Solubility in Supercritical Carbon Dioxide of Hyperbranched Copolyesters

Abstract

Hyperbranched polymers (HBPs) have been known and extensively investigated for over two decades. However, there are still areas that need to be explored. Recently, much effort has been placed in developing drug delivery systems based on macromolecules of three-dimensional structure. This paper describes the synthesis of random hyperbranched copolyesters of 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) and ε-caprolactone (ε-CL) and their phase behavior in supercritical carbon dioxide (scCO2) after modification with fluorinated anhydrides or chlorotrimethylsilane. The structure of the copolyesters was investigated by means of 1H and 13C NMR, FTIR spectroscopies, and MALDI-TOF spectrometry. The influence of the content of chain extender units of 6-hydroxyhexanoic acid (formed from ε-CL) and terminal group functionalities on the solubility of hyperbranched polymers was investigated. The phase behavior of the polymers in supercritical carbon dioxide was explored as a function of concentration and temperature. It was shown that introduction of small amounts (5–10%) of chain extender units into the dense structure of branched poly(bis-MPA) facilitates solubility of a polymer in scCO2. Viscosity and contact angle measurements were performed for the synthesized polymers.