Hydrophilic bacterial polyesters modified with pendant hydroxyl groups

Poly-3-hydroxyalkanoates (PHAs) containing pendant diol groups were prepared by the chemical modification of unsaturated PHAs using potassium permanganate (KMnO4) at 20 degrees C, without a severe reduction in molecular weight. The introduction of hydroxyl groups in the products was verified from the IR, H-1 and C-13 NMR spectra. The degree of hydroxylation increased to approximately 60% after 3 h of reaction, but there was no further increase for the longer reaction times, and the degree of hydroxylation of products was almost constant at 50-60% after 3 h, irrespective of the unsaturated unit content of the original PHOUs or of the KMnO4/unsaturated unit molar ratios, which varied from 0.7 to 2.0. The polymers which were 40-60% hydroxylated were completely soluble in polar solvents including an 80/20 acetone/water mixture, methanol and DMSO, indicating a considerably enhanced hydrophilicity of the modified PHAs. (C) 1999 Elsevier Science Ltd. All rights reserved.