Polyesterifications, lipase-catalyzed

Polyesters have been obtained in organic medium by polyesterification of hydroxy acids,328,329 hydroxy esters,330 stoichiometric mixtures of diols and diacids,331-333 diols and diesters,334-339 and diols and cyclic anhydrides.340 Lipases have also been reported to catalyze ester-ester interchanges in solution or in die bulk at moderate temperature.341 Since lipases obviously catalyze the reverse reaction (i.e., hydrolysis or alcoholysis of polyester), lipase-catalyzed polyesterifications can be regarded as equilibrium polycondensations taking place in mild conditions (Scheme 2.35). 

Linear polyurethanes, 26 Linear step-growth polymerizations, 13 Lipase-catalyzed polyesterifications, 83 Lipases, 82, 84 catalytic site of, 84 Liquefied MDIs, 211, 226-227 Liquid carbon dioxide, 206 Liquid-castable systems, 201 Liquid crystal devices (LCDs), alignment coating for, 269-270 Liquid crystalline aromatic polyesters, 35 Liquid crystalline polyesters, 25, 26, 48-53... 

Binns, F., Harffey, P., Roberts, S.M. and Taylor, A., Studies of lipase-catalyzed polyesterification of an unactivated diacid/diol system. J. Polym. Sci. A Polym. Chem., 1998, 36, 2069. 

Normally, polyester synthesis is performed by ester interchange reactions or by direct esterification of hydroxyacids or diacid/diol combinations. The use of chemical catalysts for these reactions requires harsh reaction conditions (e.g. temperatures > 200 C) as well as metal catalysts that may be problematic for certain product end-uses. These reaction conditions can limit product molecular weight and eliminate the possibility of using building blocks that are not stable at such temperature-catalyst conditions. Lipase-catalyzed polyesterifications have the potential to overcome some or all of these difficulties. 

Polyesterifications of various diacids/diols and linear hydroxy acids were studied using lipase-catalysis. The different diols studied include 1,4-butaiw, 1,6-hexane, and 1,8-octane diol. The diacids studied include succinic, glutaric, adipic, and sebacic acid. The different hydroxy acids studied were 6-hydroxyhexanoic acid, 10-hydroxydecanoic acid, 12-hydroxydodecanoic acid, and 16-hydroxyhexadecanoic. The effect of the chain length of the diol and diacids and hydroxy acids on the build-up of polymer chains by lipase-catalyzed polycondensation reactions was studied. The effect of reaction parameters on product molecular weight averages and chain dispersity were assessed. 

Figure 4. Lipase-catalyzed polyesterification of linear alphatic (O-hydroxyacids (HA) (10% wt/wt catalysUmonomer substrates, 9(fC, in bulk, with application of vacuum) extent of chain growth as a function of time The error bars were calculated from triplicate runs...

Regarding polyesters, Russell and coworkers reported the lipase (Novo-zyme-435)-catalyzed polycondensation of various triols and divinyl adipate for the synthesis of polyesters having pendant hydroxy groups (Scheme 28) [109]. Before this report, the divinyl adipate was reported to be available for enzymatic polyesterification of diols by Kobayashi and coworkers [110,111], in which the equilibrium of esterification is shifted in the forward direction by tautomerization of the eliminated vinyl alcohol to acetaldehyde. The Mw values of the resulting polyesters varied according to the triol used and ranged from 3000 to 14 000. Analysis by MALDI-TOF mass... 

Scheme 2.2 Lipase (Novozym-435)-catalyzed polyesterification of l,3-bis(3-carboxypropyl)tetramethyl disiloxane with alkanediol (p = 2, 3 and 4), in the bulk, at 70 C under reduced pressure [21], Reproduced with permission (Copyright 2008, Elsevier).

Scheme 2.4 Lipase (Novozym-435)-catalyzed synthesis of silicone aromatic polyester (SAPE) by polyesterification of a,(W-(dihydroxy alkyl)-terminated poly(dimethylsiloxane) (m = 7, n = 30 and = 2500 g mol ) with dimethyl terephthalate in toluene at 80°C under reduced pressure [26]. Reproduced with permission (Copyright 2009, The Royal Society of Chemistry).

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