title: Biosynthesis and properties of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) polymers.
abstract: In support of programs to identify polyhydroxyalkanoates with improved materials properties, we report on our efforts to characterize the mechanical and thermal properties of copolyesters of 3-hydroxybutyrate (3HB) and 3-hydroxyhexanoate (3HHx). The copolyesters, having molar fraction of 3HHx ranging from 2.5 to 35 mol % and average molecular weights ranging from 1.15 x 10(5) to 6.65 x 10(5), were produced by fermentation using Aeromonas hydrophila and a recombinant strain of Pseudomonas putida GPp104. The polymers were chloroform extracted and characterized by solution-state and solid-state nuclear magnetic resonance (NMR) spectroscopy and a variety of mechanical and thermal tests. Solution-state (1)H NMR data were used to determine polymer composition-of-matter, while solution-state (13)C NMR data provided polymer-sequence information. Solvent fractionation and NMR spectroscopic characterization of these polymers showed that polymers containing up to 9.5 mol % 3HHx had a Bernoullian compositional distribution. By contrast, polymers containing more than 9.5 mol % 3HHx had a bimodal polymer composition. Solvent fractionation of these 3HHx-rich polyesters produced two polymer fractions, each of which was again consistent with Bernoullian polymerization statistics. Solid-state NMR relaxation experiments provided insight into aging in poly(3HB-co-3HHx) copolymers, demonstrating increased polymer-chain motion with increasing 3HHx content. The elongation-to-break ratio in the polyesters increased with increasing molar fraction of 3HHx monomers. Aging properties of the poly(3HB-co-3HHx) copolymers were very similar to copolymers of 3HB and 3-hydroxyvalerate (3HV). However, poly(3HB-co-3HHx) exhibited increased activation energy to thermal degradation with increasing 3HHx content.
authors.affiliation: Monsanto Company, 800 North Lindbergh Boulevard, St. Louis, MO 63167, USA. jawed.asrar@monsanto.com
authors.forename: Jawed
authors.initials: J
authors.lastname: Asrar
authors.forename: Henry E
authors.initials: HE
authors.lastname: Valentin
authors.forename: Pierre A
authors.initials: PA
authors.lastname: Berger
authors.forename: Minhtien
authors.initials: M
authors.lastname: Tran
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Padgette
authors.forename: Joel R
authors.initials: JR
authors.lastname: Garbow
mesh_terms: D020155:3-Hydroxybutyric Acid / Q000737:chemistry* / Q000378:metabolism; D016980:Aeromonas hydrophila / Q000378:metabolism; D001672:Biocompatible Materials / Q000737:chemistry* / Q000378:metabolism; D002208:Caproates / Q000737:chemistry* / Q000378:metabolism; D003460:Crystallization; D005285:Fermentation; D009682:Magnetic Resonance Spectroscopy; D008422:Materials Testing; D016958:Pseudomonas putida / Q000378:metabolism; D013314:Stress, Mechanical; D013696:Temperature; D000094122:Polyhydroxybutyrates
chemical_list: D020155:3-Hydroxybutyric Acid; D001672:Biocompatible Materials; D002208:Caproates; C115940:poly(3-hydroxybutyrate-co-3-hydroxyhexanoate); D000094122:Polyhydroxybutyrates