Polyester chain length

Polyurethanes were found to be biodegradable by the enzyme, fungi, and yeast studied. In the case of poly(ester-urethanes) a relation between the polyester chain length of the copolymer... 

Lipase-catalyzed synthesis of PBS is a recently developed method, which is fulfilled at milder conditions without remnant metal salt. In 2006, Azim et al. (2006) reported Candida antarctica lipase B catalyzed synthesis of PBS from the monophasic reaction mixtures of diethyl succinate and 1,4-butanediol. The reaction temperature played an important role in determining the molecular weight of PBS. After polymerization for 24 h in diphenyl ether, PBS with of 2,000,4,000, 8,000, and 7,000 was produced at 60, 70, 80, and 90°C, respectively. The low molecular weight was due to precipitation after polymerization for 5-10 h, limiting the growth of the polyester chain length. Increasing the polymerization temperature from 80 to 95°C can result in the maintenance of a monophasic reaction mixture after 21 h, which led to production of PBS with of 38,000 and polydispersity index of 1.39. 

HydTOX5 proline-derived polyesters are usually readily soluble in a variety of organic solvents (benzene, toluene, chloroform, dichloro-methane, carbon tetrachloride, tetrahydrofuran, dimethylformamide, etc.) As expected, the solubility in hydrophobic solvents increased with increasing chain length of the N protecting group, while the solubility in polar solvents decreased. For example, poly(N-hexanoyl-hydroxyproline ester) is slightly soluble in ether but easily soluble in acetonitrile, while poly(N-palmitoylhydroxyproline ester) is readily soluble in ether but virtually insoluble in acetonitrile. 

Precise knowledge of the critical point is not required to determine k by this method because the scaling relation holds over a finite range of p at intermediate frequency. The exponent k has been evaluated for each of the experiments of Scanlan and Winter [122]. Within the limits of experimental error, the experiments indicate that k takes on a universal value. The average value from 30 experiments on the PDMS system with various stoichiometry, chain length, and concentration is k = 0.214 + 0.017. Exponent k has a value of about 0.2 for all the systems which we have studied so far. Colby et al. [38] reported a value of 0.24 for their polyester system. It seems to be insensitive to molecular detail. We expect the dynamic critical exponent k to be related to the other critical exponents. The frequency range of the above observations has to be explored further. 

Keywords. Bacterial polyester, Medium-chain-length poly(3-hydroxyalkanoates), Pseudomonas oleovorans, Pseudomonas putida, Functional poly(3-hydroxyalkanoates), Short-chain-length poly(3-hydroxyalkanoates)... 

The polymerase is stereospecific. It accepts only the D-(-)-stereoisomer which is generally formed by the NADPH-linked reductase. With respect to chain length of the activated fatty acids the specificity of the polymerase varies in different organisms. It links not only C4 3-acyl moieties but also C5 compounds when forming the polyester molecule [26]. It also polymerizes 3-hy-droxy-, 4-hydroxy-, and 5-hydroxyalkanoates from C3 to C5 monomers, but not C6 or higher (e.g., in R. eutropha) [27-31]. In pseudomonads, in contrast, it links C6 to C14 3-hydroxyalkanoyl-CoA [32]. 

There is considerable interest in synthesizing copolymers. This is actually possible if organisms are confronted with mixtures of so-called related and unrelated substrates. Copolymers can also be synthesized from unrelated substrates, e.g., from glucose and gluconate. The 3-hydroxydecanoate involved in the polyester is formed by diversion of intermediates from de novo fatty-acid synthesis [41,42]. Related , in this context, refers to substrates for which the monomer in the polymer is always of equal carbon chain length to that of the substrate offered. Starting from related substrates, the synthesis pathway is closely connected to the fatty-acid /1-oxidation cycle [43]. In Pseudomonas oleovor-ans, for example, cultivated on octane, octanol, or octanoic acid, the synthesized medium chain length polyester consists of a major fraction of 3-hydroxyoc-tanoic acid and a minor fraction of 3-hydroxyhexanoic acid. If P. oleovorans is cultivated on nonane, nonanol, or nonanoic acid, the accumulated polyester comprises mainly of 3-hydroxynonanoate [44]. 

Like other emulsifiers, an EUP forms micelles at a critical micelle concentration (CMC). For comonomer-free EUP-emulsions of the (MA+HD)- type the CMC is about 5 X 10"4 g/ml [115,118]. The CMC depends on the composition and chain length of the polyester, the presence of an electrolyte [118] and the temperature. 

Fig. 20. Plot of the exponent ras a function of the chain lengths between two branching points. Open symbols results by Colby et al. [118,119] for branched polyesters. The variation of this length was achieved by co-condensation of trifunctional monomers with increasing fraction of bifunctional units. Filled symbols refer to polydicyanurates (N Nj ), anhydride cured phenyl monoglycidyl ether with a small fraction of bisphenol A diglyci-dylether as crosslinker (N=8Nj ) and end-functionalized 3-arm polystyrene stars crosslinked by diisocyanate (N 40 N ). N denotes the number of repeating units between two branching points...

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