Functional chiral polyesters

Figure 7.2 Chemical structures of biobased polyesters, (a) General structure of PHA (b) example of a functional PHA harbouring 5-Phenylvaleryl-, Cyclohexylbutyryl-, 4-Pentenoyl-, 9-Cyanononanoyl-, 5-Methylhexanoyl-, and 8-Bromooctanoyl groups (c) PHA after post-synthetic functionalization (d) PHA with linker group (e) functional PHA active against biofouling [25]. Chiral centres exist at the central carbon atoms indicated by a, b and d-i c indicates the non-chiral center of 4HB 126],...

A symmetrical hydroxy diester, dimethyl )3-hydroxyglutarate, was enantios-electively polymerized by lipase catalyst to produce a chiral oligomer (dimer or trimer) with 30-37% ee (88). The enantioselective polymerization of -substituted-e-hydroxy esters took place in the presence of PPL catalyst, yielding optically active oligomers (DP < 6) (89). The enantioselectivity increased as a function of bulkiness of the monomer substituent. Optically active polyesters with molecular weight more than 1x10 were obtained by the copolsrmerization of the racemic oxyacid esters with methyl 6-hydroxyhexanoate. 

Optically active polymers are important functional materials for several industrial and bio-m ical applications and are extensively used as chiral catalysts for asymmetric synthesis, packing materials of chromatographic columns and chiral materials for the preparation of liquid crystal polymers (7). Polymers such as poly hydroxy alkanoates (PHAs), naturally occurring microbial optically active polyesters, are important materials in biomedical applications owing to their biodegradability (2). In synthetic polymer chemistry, synthesis of optically active polymers has been one of the most challenging tasks. Most synthetic chiral polymers are prepared from optically pure starting materials which are, except when isolated from nature, in limited supply and difficult to prepare (7, 3). 

Functional polyesters were synthesized through the specific catalysis of lipase, and their properties and functions were evaluated. Enantio- and regioselec-tive polycondensations produced chiral and sugar-containing polyesters, respectively [20,23]. Using lipase catalyst reactive polyesters were conveniently obtained, some of which were crosslinked to biodegradable coatings. Recently, polyester-based biomaterials have been developed by lipase-catalyzed polymerizations. 

Cammas-Marion, and S., Guerin, Ph., 2000,4-Alkyloxycarbonyl-2-oxetanones and 3-alkyloxycarbonyl-2-oxetanones as versatile chiral precursors in the design of functionalized polyesters with a controlled architecture. Des. Monomers Polym. 3(1) 77-93. 

Monne, C., Robic, D., Campion, G., Bourbouze, R., Rimbault, A., Masure, M., Langlois, V., Hemery, P., and Guerin, Ph., 1996, Enantiospecific enzymic preparation of (2S,3S)-3-alkylaspartic acids of current interest in the synthesis of stereoregular poly( p(2S,3S)-3-alkylmali acids) as new optically active functional polyesters. Chirality 8 300-304. 

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