Polyester chain length synthesis

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. 

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]. 

These modifications include variations on the length of the spacer which connects the azobenzene and the polymeric chain in side-chain azopolymers, or the electronic nature of substituents at the azobenzene moiety (Ruhmann, 1997). This requires the synthesis of appropriate monomers. Conventional techniques can be used for the polymerization of azobenzene monomers. For instance, step polymerization has been used by Hvilsted and co-workers to synthesize different series of liquid crystalline polyesters with potential applications in reversible optical data storage. These polyesters have a side-chain architecture, which synthesis is represented in Fig. 16.6 (Hvilsted et al, 1995). Being a modular synthetic approach, the influence of different structural parameters on the photoinduced optical properties can be evaluated in relatively simple manner. 

Rausch also reported the synthesis of polyurethanes however, these polymers exhibited low solubihty and they precipitated from solution during the polymerization reactions. Polyurethanes with polyether segments in their backbones have also been synthesized. It has also been reported that polyurethanes with ferrocenyl units in their backbones exhibit enhanced thermal stability. Polyesters containing ferrocenyl units in the mainchain have been the focus of numerous studies. It has been reported that many of these organometallic polymers exhibit liquid crystalline properties. " Scheme 25 shows the synthesis of a liquid crystalline polyester (103) via polycondensation reactions. Increasing the length of the alkyl chains decreased the thermal stability and glass transition temperatures of these polymers. 

---