Poly 3-hydroxyhexanoic acid

The in vivo tissue reactions and biodegradations of poly(3-hy-droxybutyrate-co-3-hydroxyhexanoate), and other polymers have been evaluated by subcutaneous implantation in rabbits. The results revealed that the degradation rate increased in the order of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxy-hexanoate), poly(lactic acid) (PLA). During the implantation period, the crystallinity of p oly(3-hydroxybutyrate-co-3-hydroxyhexanoate) increased from 19% to 22% and then dropped to 14%. The results suggest that a rapid degradation occurs in the amorphous region rather than in crystalline region (21). 

The degree of crystallinity of solvent cast copolymer films decrease from 60 to 18% when the fraction of 3-hydroxyhexanoic acid is increased from 0 to 25 niol-%. This finding suggests that the 3-hydroxyhexanoic acid units are excluded from the crystalline phase of 3-hydroxybutyric acid. The rates of enzymatic erosion increase markedly with the increase of 3-hydroxyhexanoic acid the 

A latex of poly(/3-hydroxyoctanoate) can be obtained from the bacterium Pseudomonas oleovorans grown on sodium octanoate at a high cell density (22). In the course of purification sodium hypochlorite was used. It was observed that latex stabilization occurred spontaneously due to the persistence around the polymer granules of the murein sacculus, which envelopes the bacterial ceU. It was shown that the optimal conditions for the bacteria digestion correspond to a sodium h ochlorite concentration of 21-26 mmolg.  

The resulting films display the t ical properties of a thermoplastic elastomer. Depending on the conditions of purification, also fully amorphous poly(/3-hydroxyoctanoate) films can be obtained. Nanocomposite materials can be prepared when using this latex as a matrix and using in addition a colloidal suspension of hydrolyzed starch or cellulose whiskers as a natural and biodegradable filler. The properties are strongly dependent on the aspect ratio of the whiskers (23). 

Poly(3-hydroxyoctanoate) with pendant carboxylic groups have been prepared by the chemical modification of unsaturated bacterial polyesters. The oxidation of the pendant alkene groups is complete and thereby a loss in molecular weight of polymer was observed. The introduction of pendant carboxylic groups enhances the hydrophilic character of the polymers (24). 

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Block terpolymers of poly(hydroxyoctanoic acid), poly(hydroxyhexanoic acid) and poly(hydroxydecanoic acid), and the so-called bacterial elastomers , produced by bacteria [124] also belong to the polyester thermoplastic elastomer family (see also Chapter 2). 

PHBH poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid)... 

Hakkarainen [19,36] Poly(vinyl chloride)/ polycaprolactone-carbonate blend Thermo-oxidation, hydrolysis 6-Hydroxyhexanoic acid, caprolactone PDMS-DVB... 

Fig. 5 GC-MS chromatograms of the low molecular weight products extracted from poly- caprolactone films (a) unaged film (b) after 2 weeks in abiotic medium and (c) after 2 weeks in biotic medium. The identity of numbered peaks is 1 = caprolactone 2 = 6-hydroxyhexanoic acid 4 = cyclic dimer 7 = cyclic trimer and 3,5,6 = phthalates. Reprinted from [60] with permission of Wiley-VCH Verlag GmbH Co. Wiley-VCH Verlag Gmbh 8c Co (2002)...

PHB-co-PHV [54] is obtained from Azotobacter chroococcum [58, 63). The biodegradation is slower for the copolymers than poly-3-hydroxybutyrate. 3-hydroxy-n-phenylalkanoic acids and 3-hydroxyaliphatic acids are obtained from Pseudomonas putida [59]. Poly (3-hydroxyoctanoic acid) and poly (6-hydroxyhexanoic acid) and poly (3-hydroxyoctanoic acid) [64], Poly-(R)-3-hydroxybutyrate/polyphosphate (PHB/polyP) complexes are isolated from the plasma membranes of bacteria [65,66]. Polyhydroxyoctanoate is produced by feeding octanoic acid to Pseudomonas oleovorans [67]. 

Encyclopedia of materials science and technology. Elsevier, Oxford, pp 448 53 Abe H, Kikkawa Y, Aoki H, Akehata T, Iwata T, Doi Y (1999) CrystaUization behavior and thermal properties of melt-crystaUized poly[(/J)-3-hydroxybutyric acid-co-6-hydroxyhexanoic acid] films. Int J Biol Macromol 25 177-183... 

Valentin HE, Dennis D (1997) Production of poly(3-hydroxybutyrate-co- 4-hydroxybutyrate) in recombinant Escherichia coli grown on glucose. J Biotechnol 58 33—38 Valentin HE, Lee EY, Choi CY, Steinbuchel A (1994) Identification of 4-hydroxyhexanoic acid as a new constituent of biosynthetic polyhydroxyalkanoic adds from bacteria, Appl Microbiol Biotechnol 40 710-716... 

Moreover, P3HB shows a crystalline structure because of its stereoregularity similarity to isotactic polypropylene. In order to improve mechanical properties and processability, and thus to obtain a more flexible material, P3HB copolymers are nowadays used. The first attempt to synthesize a random copolymer is a blend of 3-hydroxybutanoic acid and 3-hydroxyvaleric acid, obtaining poly(3-hydroxybutyrate-co-3-hydroxyvalerate) P(3HB-co-3HV) copolymer. Other blends are obtained using, for example, hydroxyhexanoic acid, 4-hydroxybutanoic acid, and hydroxyoctanoic acid. Physical and mechanical properties of these copolymers have been reported (Lee and Park, 2005, Marchessault and Yu, 2005, Williams and Martin, 2005) as well... 

Poly( -caprolactone), PCL, comprised of hexanoate repeating units, is the most important synthetic biodegradable aliphatic polyester among the poly(direct polycondensation reaction. Thus, poly(s-caprolactone) is mainly produced by ROP of the cyclic... 

Poly(3-hydroxybutyric acid-co-3-hydroxyhexanoic acid) [P(3HB-co-3HH)] is another bacterial copolyester. Our laboratory has found that random copolyesters of 3HB with 3HH are produced from plant oils by the Aeromonas caviae bacterium isolated from soil The basic characterization on the crystallization and physical properties of P(3HB-co-3HH) random copolyesters with 3HH contents varying from 0 to 25 mol% has indicated that 3HH units are excluded from the P(3HB) crystal lattice, and that both the crystallinity and crystallization rate are reduced as 3HH content increases. The elongation at break of the copolyester film is near 10 times that of P(3HB) homopolymer . These results have shown that the mechanical properties of P(3HB-co-3HH) random copolyesters can be modified although they have the same crystal structure of P(3HB) homopolymer, and they suggested that the copolyesters have better processability and more extensive applicable areas. 

The bacterial copolyesters of (/ )-3-hydroxybutyric acid (3HB) and (/ )-3-hydroxyhexanoic acid (3HH) [P(3HB-co-3HH)] were supplied from Procter Gamble Company. Poly[(R)-3-hydroxybutyric acid] was supplied... 

Abe, H., Kikkawa, Y., Aoki, H., Akehata, T., Iwata, T., and Doi, Y., 1999, Crystallization behavior and thermal properties of melt-crystallized poly[(R)-3-hydroxybutyric acid-co-6-hydroxyhexanoic acid] films. Inter. J. Biol. Macromol. 25 177-183. 

It was found meanwhile that nearly every slim unbranched polymer chain, such as poly(trimethylene oxide) [224], poly(l,3-dioxolane) [225], poly(tetramethylene oxide) [226], polyethylene imine) [227], poly(3-hydroxy propionate), poly (4-hydroxybutyrate) and poly(6-hydroxyhexanoate) [228,229], poly(butylene succinate) [229], polyadipates [230], nylon-6 [231], and even oligomers of polyethylene [232], form a-CD ICs with channel structures. In all of these cases, inclusion is a heterogeneous process, since the guest polymer and its CD complex are almost insoluble in water. Therefore, extensive sonication had to be applied to accelerate the diffusion process. The polymer was also dissolved in an organic solvent, e.g., nylon-6 in formic acid, and this solution was added to the solution of a-CD [231], Alternatively, a monomer, such as 11-aminoundecanoic acid, was included in a-CD and polymerized to nylon-11 by solid state polycondensation within the channels of the IC. Thus, the IC of nylon-11 was formed under conservation of the crystal packing [233-235],... 

For large-scale recombinant production of bacterial polymers, non-polymer producing bacteria were exposed to biosynthesis pathways. Polymers such as PHA, CGP (cyanophycin granule peptide), HA (hyaluronic acid), and PGA [poly-y-glutamate] were produced by these methods [89, 85-96]. For example, recombinant E.coli [89] was fermented for the lai e-scale production of PHA [89]. In addition the PHB biosynthesis genes of Ralstonia eutropa were harbored in E.coli to produce poljmers such as PHA composed of (R)-S-hydroxybutyrate and (R)-3-hydroxyvalerate and/or (R)-3-hydroxyhexanoate which showed preferable properties for use in industrial applications [97-99, 85-96]. 

Other approaches to improve the properties of PHB is the production of derivatives based on PHB via the biosynthesis of copolyesters containing PHB units with other 3-hydroxyalkanoates units [19], such as poly [3-hydroxybutyrate-co-hydroxyvalerate] [PHBV] [20] or poly [3-hydroxybutyrate-co-3-hydroxyhexanoate] [21], with different molar ratios of hydroxycarboxylic acids. This approach has been investigated extensively [22] because it can... 

The metabolic pathways utihzed to produce poly[(/ )-3-hydroxybutyrate-co-(/ )-3-hydroxyhexanoate] (PHBHx) copolymer is shown in Fig. 4 (Noda et al. 2005a). Two units of acetyl-CoA forms the acetoacetyl-CoA with phaA thiolase, which is then converted to 3-hydroxybutyryl-CoA with phaB reductase. Parallel to these steps are the other metabolic pathways involving fatty acid biosynthesis (phaG) and... 

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