AA-BB Type Enzymatic Polyesterification

Okumara and co-workers [10] were the first to attempt the lipase-catalyzed synthesis of oligoesters from reactions between diols (AA) and dicarboxylic acids (BB). They showed that trimer , pentamer , and heptamer consisting of AA-BB-AA, AA-BB-AA-BB-AA, and AA-BB-AA-BB-AA-BB-AA, respectively, were formed. Klibanov et al. [121] used the stereoselectivity of lipases to prepare enantioen-riched oligoesters. The reactions were conducted using racemic diester and an achiral diol or, conversely, a racemic diol and an achiral diester as monomers (see also Chapter 11). 

Lipase-catalyzed synthesis of poly(l,4-butyl sebacate) from reactions of 1,4-butanediol and sebacic acid or activated derivatives of sebacic acid were studied by Linko et al. [51]. Reactions between 1,4-butanediol with sebacic acid, 

The same research group using the lipase from Mucor miehei in diphenyl ether (11.1% w/v) studied copolymerizations of an aromatic diacid (terephthalic or isophthalic) and an aliphatic diol (1,4-butane- or 1,6-hexanediol) [50]. Even at temperatures up to 70 °C, polymerizations of these aromatic diacids were unsuccessful. However, using Novozym 435 as catalyst, polymerizations of aromatic diacids were accomplished, with yield ranging 85-93%. For example, while the Novozym 435-catalyzed reaction of isophthalic acid with butanediol yielded oligomers, a similar reaction between the C-6 diol and isopthalic acid at 70 °C yielded a polymer with = 55000. 

Kobayashi and co-workers [48] studied the potential of carrying out condensation reactions in solventless or bulk reactions. They reported the preparation of aliphatic polyesters with Mu, 10000 by reacting sebacic acid with 1,4-butanediol in a solvent-free system, under reduced pressure, using CALB as catalyst. 

The phase separation of reactants hindered attempts to carry out lipase-catalyzed synthesis of poly(butylene succinate) (PBS) from succinic acid and 1,4-butanediol via dehydration. Therefore, in order to obtain a monophasic reaction mixture, dimethyl succinate was used in place of succinic acid. [49] The reaction mixture remained monophasic during the reaction course, and after 21 h at 95 °C PBS with M of 38000 was obtained. 

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