Green Route to Prepare Renewable Polyesters from Monomers: Enzymatic Polymerization 225
Two-stage
diphenyl ether
N435
O HO
O
O
O
O O
OO
O
O
O
O
H
y
O
n= 2, succinate; n= 3, glutarate; n= 2, adipate; n= 6, subarate; n= 8, sebacate; n= 10, dodecanedioate;
O
O
x
OO
n
n
+ + OH
Figure 7.4Lipase-catalyzed synthesis of bio-based polyester via a two-stage method in diphenyl
ether.
with highest specificity for diethyl adipate. Deterioration of the double bond is the main
side reaction observed when itaconic acid is used as a monomer to synthesize polyester
using conventional polymerization techniques. No deterioration of the double bond
has been observed due to the chemoselectivity of lipase and the ability to achieve
the polymerization process under mild reaction conditions when enzyme is used as
catalyst.
7.4.2 Dicarboxylic Acid or Its Esters with Polyols
Presence of pendant functional groups, for example, hydroxyl, carboxylic acid, or mer-
capto, within the structure of polyesters is of great interest as they can affect the physical
and mechanical properties of the resulting polymer, for example, increase solubility of
polymer in water, or can be potentially used later to attach some interesting molecules
onto the polymer chain, such as drug or fluoresce dye, or allow to attach further polymer
chains in order to modify the mechanical, biological, and physical properties to meet
the technical needs of many applications. The regioselectivity of enzymes enables the
syntheses of linear or nearly linear polyesters in one step starting from multifunctional
monomers (functionality≥3). Thus, many interesting bio-based polyols such as glycerol,
sucrose, have been investigated for potential use as a building block to prepare linear
polyesters with free hydroxyl (OH) pendant groups. The first report appeared in 1991,
in which water-soluble sucrose oligoesters with DP of 11 were successfully synthesized
with high regioselectivity by reacting sucrose and bis(2,2,2-trifluoroethyl) sebacate in
pyridine at 45∘C for 5 days using the protease Proleather as a catalyst. Russell and his
coworkers reported lipase-catalyzed synthesis of polyester with free pendant OH by
the reaction of divinyl adipate with triols of various lengths at 50∘C for 24 h [78]. The
resulting polyesters haveMwranging from 3 to 14 kDa based on the kind of triol utilized.
The authors demonstrated that the utilized reaction conditions resulted in polyester
with free OH pendant groups that are 90–95% secondary and 5–10% primary without
evidence for network formation. Deeper investigation of previous reaction was carried
out later by Kobayashi and his coworkers where they studied the factors, that is, reaction
temperature, lipase origin, feed ratio of monomers, and influencing stereoselectivity of
lipase-catalyzed polycondensation reaction between divinyl sebacate and various diols
(Figure 7.5) [79]. The report showed a perfect control of polymerization regiospecific at
