An unusual bacterial polyester with a phenyl pendant group

The microorganism Pseudomonas oleovorans is known to produce polyesters containing 3-hydroxyalkanoate units when grown on n-alkanes and n-alkanoic acids under nutrient limiting conditions, but when 5-phenylvaleric acid was supplied as the only carbon source, poly3-hydroxy-5-phenylpentanoate], a polyester with a phenyl pendant group, was produced. The optimum substrate concentrations and harvesting times were determined by measuring the change of cell growth and polymer yield during the growth. A 12-L cell culture yielded 222,5 mg polymer/L and 25% polymer per cellular dry weight. This bacterial polymer showed an optical rotation of α] = ?24,5° ± 0,2°. The structure was corroborated by ¹H NMR and ¹³C NMR spectroscopy. The composition of the polymer was also determined by methanolysis to the methyl ester of the repeating unit, which was subsequently analyzed by GC. By this procedure the polyester was found to be a homopolymer to the extent of at least 99%. The polyester has a glass transition at 13°C, a melting range from 54 to 69°C, and a weight-average molecular weight of M?_w = 350000 with a polydispersity M?_w/M?_n of 3,5, as determined by GPC relative to polystyrene standards.