Poly Hydroxyalkanoate s PHAs

Scale-up studies in the absence of solvent allowed the production of important quantities of PHB oligomers in satisfactory yields. 

---

Poly(3-hydroxybutyrate) is a biopolymer produced by numerous bacteria in nature as an intercellular carbon and energy reserve and belongs to the class of poly (hydroxyalkanoate)s (PHAs). In 1925, the French microbiologist Maurice Lemoigne discovered and characterized PHB extracted from Bacillus megaterium. However, it is produced by a various number of microorganisms such as Cupriavidus necator or Ralstonia eutroph. PHAs are biodegradable polyesters with a structure as shown in Fig. 1. 

A last category may be identified in polymers produced by native microorganisms or genetically transformed bacteria. The best known example of this category is constituted by poly (hydroxyalkanoate)s (PHA), mainly poly (hydroxybutyrate) (PHB) and copolymers of hydroxy-butyrate and valerate produced by Monsanto and Metabolix under the trade name Biopol. 

Another interesting example of lactones are the p-hydroxyalkanoates, whose ROP affords poly(p-hydroxyalkanoate)s (PHAs), a class of aliphatic polyesters naturally produced by bacteria (Fig. 3) [12, 13]. Poly(3-(R)-hydroxybutyrate) (PHB) is a typical example. PHB is a stiff thermoplastic material with relatively poor impact strength, but the incorporation of other monomers can improve the mechanical properties. 

Aliphatic polyesters are the most representative examples of biodegradable polymeric materials. Poly(3-hydroxyalkanoate)s, PHA, are well known biocompatible and biodegradable polyesters that are produced by various microorganisms as carbon and energy reserves. The physical properties of PHAs vary from crystalline-brittle to soft-sticky materials depending on the length of the side aliphatic chain on p carbon ... 

Abstract Hyphenation of electrospray ionization witii ion-trap multistage mass spectrometry (ESI-MS°) provides charactoisation of subtle molecular structure of both syntiietic and natural aliphatic polyesters as well as oligomeric products of their biodegradation. Implementation of multisti e MS technique for structural studies of the novel bio-inspired polymers including poly[(R,S)-3-hydroxybutyrate], a-PHB, telechelics and a-PHB conjugates with oligopeptides has been demonstrated. The novel results concerned with evaluation of the subtle structure of macroinitiators obtained by partial depolymerisation of selected natural poly(3-hydroxyalkanoate)s, PHA, are also presented. 

Alcaligenes eutrophus has been used for industrial production of poly(hydroxyaIkanoate)s (PHAs). PHA is prepared from acetyl CoA in three steps and the last step is the chain growth polymerization of hydroxyalkanoate CoA esters catalyzed by PHA polymerase, yielding PHA of high molecular weight, which has heen in vitro examined, leading to synthesis of PHAs with well-defined structure. This synthetic process obeys the biosynthetic pathways (see Poly(3-H DROXYALKANOATES)). 

Figure 6.1 Classification of biodegradable polyesters according to their origin with selected examples PHAs, poly(hydroxyalkanoate)s PLA, poly(lactic acid) PCL, poly( -caprolactone) PBS, poly(butylene succinate).

The general formula of poly(hydroxyalkanoate)s is given in Scheme 6.8. The majority of PHAs have the same three-carbon backbone but differ in the length... 

Cerrone, F., Choudhari, S. K., Davis, R., Cysneiros, D., O Flaherty, V., Duane, G., Casey, E., Guzik, M. W., Kenny, S. T, Babu, R. R, O Connor, K. Medium chain length poly-hydroxyalkanoate (mcl-PHA) production from volatile fatty acids derived from the anaerobic digestion of grass. Appl Microbiol Biotechnol 2014, 98, 611-20. 

PHA degradation, 43 PHAs. See Poly(hydroxyalkanoic acid)s (PHAs)... 

Poly(hydroxyalkanoic acid)s (PHAs), 27, 31, 41-43 biodegradable, 90 Poly(4-hydroxybenzoic acid) (PHBA), 49-50... 

Since the chemical structure and monomer composition of a specific polymer are the most important factors in determining the polymer s physical and material properties, a short recapitulation of typical representatives of microbially synthesized poly(hydroxyalkanoates) is presented in this section. A more detailed overview on this issue is available from References [19-21], but is not within our scope here. The monomer composition of PHAs depends on the nature of the carbon source and the microorganisms used. This way, numerous monomers have been introduced into PH A chains [3-9]. PHAs have been divided roughly into two classes [19]. 

Blends of poly(3-hydroxyalkanoic acid)s (PHAs) with various natural and synthetic polymers have been reported as reviewed in Refs. [21,22]. By blending with synthetic polymers it is expected to control the biodegradability, to improve several properties, and to reduce the production cost of bacterially synthesized PHAs. The polymers investigated as the blending partners of PHAs include poly(ethylene oxide) [92, 93], poly(vinyl acetate) [94], poly(vinylidene fluoride) [95], ethylene propylene rubber [94, 96], po-ly(epichlorohydrin) [97, 98], poly(e-caprolactone) [99], aliphatic copolyesters of adipic acid/ethylene glycole/lactic acid [100] and of e-caprolactone/lactide... 

Zhang LL, Xiong CD, Deng XM (1997b) MisdbUity, crystallization and morphology of poly(P-hydroxybutyrate)/poly(D,L-lactide) blends. Polymer 37 235-241 Zhang S, Kolvek S, Goodwin S, Lenz RW (2(X)4) Poly(hydroxyalkanoic add) biosynthesis in Ectothiorhodospira shaposhnikovii characterization and reactivity of the type 111 Pha synthase. Biomacromolecules 5 40-48... 

Procter Sc Gamble developed a wide range of poly(hydroxybutyrate-co-hydroxyalkanoates) [copolymers of P(3HB) and 3-hydroxyhexanoate, P(3HB) and 3-hydroxyoctanoate, P(3HB) and 3-hydroxyoctadecanoate] with the tradename Nodax. In 2007, Meredian Inc. purchased Procter Sc Gamble s PHA technology. Meredian Inc. has announced the start-up of production at full industrial level (30 ktonnes/year) in its Bainbridge facility in the second half of 2014 [21]. 

---