Carbohydrate polyester

Carbohydrate Polyesters as Fat Substitutes, edited by Casimir C. Akoh and Barry G. Swanson... 

C.C. Akon, B.G. Swanson 8eds.) Carbohydrate Polyester as Fat Substitutes Marcel Dekker NY, Basel (1994)... 

A combinatorial approach for biocatalytic production of polyesters was demonstrated. A library of polyesters were synthesized in 96 deep-well plates from a combination of divinyl esters and glycols with lipases of different origin. In this screening, lipase CA was confirmed to be the most active biocatalyst for the polyester production. As acyl acceptor, 2,2,2-trifluoroethyl esters and vinyl esters were examined and the former produced the polymer of higher molecular weight. Various monomers such as carbohydrates, nucleic acids, and a natural steroid diol were used as acyl acceptor. 

Plants were probably the first to have polyester outerwear, as the aerial parts of higher plants are covered with a cuticle whose structural component is a polyester called cutin. Even plants that live under water in the oceans, such as Zoestra marina, are covered with cutin. This lipid-derived polyester covering is unique to plants, as animals use carbohydrate or protein polymers as their outer covering. Cutin, the insoluble cuticular polymer of plants, is composed of inter-esterified hydroxy and hydroxy epoxy fatty acids derived from the common cellular fatty acids and is attached to the outer epidermal layer of cells by a pectinaceous layer (Fig. 1). The insoluble polymer is embedded in a complex mixture of soluble lipids collectively called waxes [1], Electron microscopic examination of the cuticle usually shows an amorphous appearance but in some plants the cuticle has a lamellar appearance (Fig. 2). 

Suberin, being an adcrustation on the cell wall, cannot be separated from cell walls. Instead, suberin-enriched wall preparations can be obtained by digesting away as much carbohydrate polymers as possible using pectinases and cellu-lases [3,7]. Depending on the source of the suberized cell wall preparation, the polyester part may constitute a few percent to 30% of the total mass. 

Galbis et al. described a variety of carbohydrate-based linear polyesters 61 of the poly(alkylene dicarboxylate) type that were obtained by polycondensation reactions of the alditols 2,3,4-tri-(9-methyl-L-arabinitol (9) and 2,3,4-tri-O-methyl-xylitol (10), and the aldaric acids 2,3,4-tri-(9-methyl-L-arabinaric acid (26) and 2,3,4-tri-(9-methyl-xylaric acid (27), butanediol, and adipic acid were also used as comonomers [28]. Copolyesters of the poly(aIkylene-c )-arylene dicarboxylate) type were obtained using bisphenols as comonomers (Scheme 1). Chemical polycondensation reactions were conducted in bulk or in solution. Enzymatic polycondensation reactions of adipic acid with the above-mentioned alditols were carried out successfully using Lipozyme and Novozyme 435. The hydrolytic degradations of some of these polyesters were also described. 

The 10-undecenoic acid motif has also been attached to isosorbide in the preparation of a fatty acid-/carbohydrate-based monomer [131]. ADMET polymerization in the presence of C3 and C4 produced fully renewable unsaturated polyesters (Scheme 18). Most importantly, the transesterification of these polyesters with MeOH, and subsequent analysis by GC-MS of the products, allowed for the quantification of double-bond isomerization during ADMET in a very simple manner. This strategy was then extended to fatty acid-based ADMET polyesters synthesized in the presence of indenylidene metathesis catalysts [132]. With these studies, the knowledge on the olefin isomerization in ADMET reactions was widened, and it is now possible to almost completely suppress this undesired side reaction. 

As already mentioned, there has been renewed interest for using carbohydrates as a source of chemicals since the 1980s with the development of the chemistry of furanic compounds, particularly for the preparation of nonpetroleum derived polymeric materials, such as polyesters, polyamides and polyurethanes.[17,19]... 

Polymers are very large molecules made up of repeating units. A majority of the compounds produced by the chemical industry are ultimately used to prepare polymers. These human-made or synthetic polymers are the plastics (polyethylene, polystyrene), the adhesives (epoxy glue), the paints (acrylics), and the fibers (polyester, nylon) that we encounter many times each day. It is difficult to picture our lives without these materials. In addition to these synthetic polymers, natural polymers such as wood, rubber, cotton, and wool are all around us. And, of course, life itself depends on polymers such as carbohydrates, proteins, and DNA. This chapter discusses synthetic polymers. Naturally occurring polymers are presented in Chapters 25, 26, and 27. 

It has often been proclaimed that 5-hydroxymethylfurfural (HMF, Fig. 8.35) could be an ideal cross-over compound between carbohydrates and petrochemistry [184], as it is a bifunctional heteroaromatic compound that is accessible from fructose in one step. It was expected that HMF could be developed into a valuable synthetic building block and that its derivatives, such as furan-2,5-dicarb-oxylic acid (FDA), would be able to compete with fossil-derived monomers for use in thermostable polyesters and polyamides. 

Problem 22.34 Polylactic add (PLA) has received much recent attention because the lactic acid monomer [CH3CH(0H)C00H] from which it is made can be obtained from carbohydrates rather than petroleum. This makes PLA a more environmentally friendly polyester. (A more in-depth discussion of green polymer synthesis is presented in Section 30.8.) Draw the structure of PLA. 

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