224 Introduction to Renewable Biomaterials
7.4.1 Dicarboxylic Acid or Its Esters with Diols
The first publication reported lipase synthesis of polyesters from various dicarboxylic
acids and diols appeared in 1984 where only oligomers were obtained using lipase from
Aspergillus nigeras a catalyst [64]. Binnset al. reported lipase-catalyzed synthesis of
polyesters using adipic acid with 1,4-butanediol – both monomers are derived from
glucose [65, 66] – in diisopropyl ether, which resulted in a polyester with degree of
polymerization (DP) 20 [67]. Utilization of divinyl adipate instead of adipic acid together
with 1,4-butanediol in diisopropyl ether at 45∘Cfor48hinthepresenceoflipasePCas
a catalyst afforded polyester with molecular weight of 2.1× 104 Da [68]. Interestingly,
similar polymerization was conducted in scCO 2 , environmentally friendly solvent,
instead of diisopropyl ether, which afforded the same polyester withMn3900 Da
[69]. Poly(1,4-butyl sebacate) was produced by lipase-catalyzed polycondensation of
sebacic acid with 1,5-butanediol; both monomers can be synthesized from renewable
resource, in bulk under reduced pressure yield polyester ofMn14 kDa [70]. The authors
also demonstrated increases in polyester molecular weight by increasing the length
of methylene chain of monomers. Linkoet al. [71] was able, however, to produce
poly(1,4-butyl sebacate) with molecular weight up to 42 kDa usingMucor mieheilipase
as catalyst under high vacuum. PBS is an important biodegradable polyester due to its
excellent biodegradability, thermal processability, and balanced mechanical properties
[72]. PBS can be produced by polymerization of 1,4-butanediol with succinic acid,
which is in turn synthesized by microbial fermentation of renewable feedstock such as
glucose, starch, xylose, and so on [73]. In 2006, a relatively high-molecular-weight PBS
ofMw=38 kDa was produced by polymerization of diethyl succinate and 1,4-butanediol
using N435 as a catalyst in a temperature-varied, two-stage polymerization process
[74]. In this report, the reaction temperature was increased from 80 to 95∘Cafter21h
in order to keep the resulting polymer soluble in the reaction medium.
Itaconic acid is an unsaturated carboxylic acid and considered as an important
renewable monomer for the production of polyesters. It can be obtained via fermen-
tation of carbohydrates, for example, glucose, and has a current worldwide production
of about 15,000 tons per year [75]. In fact, introducing itaconic acid as building block
yields polyester containing double bond within the main chain, which can potentially
be used later for further chemical modification, for example, crosslinking reaction.
Fully bio-based and cross-linkable polyester was synthesized by lipase-catalyzed
polycondensation of 1,4-butanediol, succinic acid, and itaconic acid using lipase CA
(lipase fromCandida antarctica) as a catalyst [76].
Only oligomers can be obtained when succinic acid and itaconic acid used in
carboxylic acid form to produce polyester, while alkyl diesters form of these monomers
resulted polyester with molecular weight and molar compositions affected mainly by
the applied polymerization method. The highest molecular weight,Mw=23 kDa, was
obtained by carrying out the enzymatic polymerization reaction under azeotropic
condition where a mixture of cyclohexane and toluene was used as solvent. Looset al.
investigated the N435-catalyzed polycondensation of bio-based dimethyl itaconate,
1,4-butanediol, and various diacid ethyl esters of methylene with a chain length of 2–10
(Figure 7.4) [77]. The authors could synthesize polyesters of molecular weight up to
94 kDa by utilizing the two-stage method in diphenyl ether. The authors demonstrated
also that N435 prefers diacid ethyl ester monomers with methylene chain length (n>2),
