Nuclear magnetic resonance studies on bacterial copolyesters of 3‐hydroxybutyric acid and 3‐hydroxyvaleric acid

Copolyesters of 3‐hydroxybutyric acid (HB) and 3‐hydroxyvaleric acid (HV), P(HB‐co‐HV), were isolated from Alcaligenes eutrophus and characterized by solution NMR, solid‐state 13C CP/MAS NMR, and differential scanning calorimetry. The 13C CP/MAS NMR analysis was compatible with that of a random copolyester of oxy‐(1‐methyl‐3‐oxotrimethylene) (B) and oxy‐(1‐ethyl‐3‐oxotrimethylene) (V) units which adopts a regular conformation of a 21 ‐helix in the solid state throughout a wide range of compositions varying from 0 to 90 mol‐% V units. The chain dynamics of P(HB‐co‐HV) in chloroform was studied by analysis of the 13C and 1H NMR spectra. The carbon‐13 spin‐lattice relaxation times (T1) and nuclear Overhauser enhancements (NOE) indicated that the copolyester molecules in chloroform are not rigid but rather flexible. The conformational preferences of the copolyester molecules were determined by analysis of the 1H NMR spectra.