Preparation of unsaturated polyesters using boric acid as mild catalyst and their sulfonated derivatives as new family of degradable polymer surfactants

Boric acid-pyridine mixture is presented as mild catalyst for polycondensation of semi-esters of ethylene glycol, in situ-generated by “cyclic anhydride–diol” reaction scheme from maleic, succinic and phthalic anhydrides. This catalyst system was demonstrated to give colorless polyesters in low molecular weights (Mn: 1650–1950 Da) within 4 h at 130 °C 1H NMR spectra of the polyesters derived from maleic anhydride revealed significant isomerization of maleate groups to fumarate units (∼80 %) during the polyesterification. Maleate and fumarate double bonds of the unsaturated polyesters (USP) were demonstrated to add bisulfite ions quantitatively to give sulfonated polyesters. The resulting sulfonated polyesters with 50% and 70% succinate units exhibited relatively narrow size spherical and ellipsoidal micelles in aqueous solutions, as inferred from surface tension, DLS and ESEM measurements. The results showed that, this procedure allows preparing a new family of polymer surfactants with tunable hydrophilicity and degradable polyester backbones.