A-B Type Enzymatic Polyesterfication

Reported hydroxyacids that are self-condensable by enzyme catalysis include 6-hydroxyhexanoic acid [25], 10-hydroxydecanoic acid [26], 5-hydroxyhexanoic acid [27], 5-hydroxydodecanoic acid [27], 11-hydroxydecanoic acid [28], 

12-hydroxydodecanoic acid [29], 15-hydroxypentadecanoic acid [27], 16-hydroxyhexadecanoic acid [25], 18-hydroxyoctadecanoic acid [30], ricinoleic acid [31, 32], cis-9,10-epoxy-18-hydroxyoctadecanoic acid [30], cholic acid [33] (see also Table 4.1). Also, alkyl esters of these compounds have been used as monomers for lipase-catalyzed polycondensation reactions. Examples include ethyl esters of 3- and 4-hydroxybutyric acid [27], methyl ricinoleate [32] and isopropyl aleuriteate [46]. 

In the following we report some of the examples of A-B type enzymatic polyesterifications. The reader should refer to Table 4.1 for further interesting examples. 

Methyl e-hydroxyhexanoate was chosen as a model monomer for the first investigation to determine how important reaction parameters that include enzyme origin, solvent, concentration and reaction time influence its self-condensation polymerization [12]. The degree of polymerization (DP) of the polyester formed followed a S-shaped behavior with solvent log P (—0.5 log P 5)-with an increase in DP around log P 2.5. Decreasing values of DP in good solvents for polyesters were attributed to the rapid removal of product oligomers from the enzyme surface, resulting in reduced substrate concentration near the enzyme. 

A time course study of 11-hydroxydecanoic acid polymerization catalyzed by Candida cylindracea lipase was reported by O Hagan and Zaidi [28]. The authors revealed that oligomers are formed relatively rapidly and then later condense to generate higher molecular weight polyesters. After 7 days, they reported formation of a polyester with molecular weights up to Mw = 35000. 

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