MICROBIAL POLYESTER SYNTHESIS - EFFECTS OF POLY(ETHYLENE GLYCOL) ON PRODUCT COMPOSITION, REPEAT UNIT SEQUENCE, AND END GROUP-STRUCTURE

Poly(ethylene glycol) of M(n), 200 g/mol (PEG-200) was added to cultiv ation media of Alcaligines eutrophus during polymer formation, and the carbon source used was 4-hydroxybutyrate. The addition of PEG-200 fro m 0 to 2 wt % resulted in increased 4-hydroxybutyrate (4HB) incorporat ion from 66 to 86 mol % into the poly(3-hydroxyalkanoate) (PHA), forme d. When 4% PEG was used, the mole percent of 4HB in PHA decreased to 6 4 mol %. Thus, PEG in cultivation media resulted in polyester composit ional changes. An unexpectedly large amount of the dry cell weight (si milar to 10%) was found to be PEG-200 for cultivation media amended wi th 4% PEG-200. Analysis of this product by gel. permeation chromatogra phy (GPC) showed it to be complex, having multiple peaks. The repeat u nit sequence distribution determined by 75 MHz C-13 NMR spectroscopy i ndicated that the addition of PEG-200 to media resulted in the formati on of a product with predominantly 3-hydroxybutyrate (3HB)-3HB and 4HB -4HB diads instead of random copolyesters which are formed in the abse nce of PEG addition to media. Two dimensional homonuclear (H-1) correl ated NMR analysis along with a number of control experiments indicates that PEG was covalently linked at the carboxy terminal position of PH A chains, forming natural-synthetic diblocks. Fractionation of this pr oduct into acetone soluble (AS, 84 mol % 4HB, M(n) = 37 400 g/mol) and insoluble (AIS, 95 mol % 3HB, M(n) = 130 000 g/mol) fractions was car ried out which proved that the product formed is a mixture of polyeste rs differing in composition and molecular weight. Analysis of the unfr actionated product as well as AS and AIS fractions by differential sca nning calorimetry supported the above conclusions.