Green Route to Prepare Renewable Polyesters from Monomers: Enzymatic Polymerization 229
to prepare various self-stabilizing nanoparticles with well-defined sizes and narrow
size distributions [95]. The shape of resulting nanoparticles depends strongly on the
length of side chains and on the degree of substitution [61]. Furthermore, the resulting
polymers showed no toxicity to HepG2 cells [96]. The ease of synthesis besides the
unique characteristic of resulting polymers strongly suggests that these polymers can
be used for nano-drug delivery or as injectable or implantable carrier for the controlled
release of active ingredient [97].
7.4.4 Polyester Using Furan as Building Block
The importance of incorporating furan moieties within the structure of polyester stems
not only from their wide availability starting from renewable resources but also from the
possibility of developing novel chemical structure with original properties simulating
the properties and applications of currently available polymers derived from fossil
resources [83]. Furan dicarboxylic acid (FDCA), for instance, is a member of the furan
family, obtained by oxidation of HMF, which is in turn derived from dehydration of
certain sugars [56, 98]. The monomer has been widely studied as a potential bio-based
alternative to a petroleum-based monomer terephthalic acid (TA), which is used
to prepare the most important commercial polyester poly(ethylene terephthalate)
(PET) [99]. Interestingly, recent studies showed superior improved barrier properties
for poly(ethylene furanoate) (PEF), which has a water diffusion coefficient 5 times
lower than that of PET besides a 10 times lower oxygen permeability [100, 101]. It is
expected, therefore, that by 2020 over 60% of global production of FDCA will be used
to produce bio-based alternatives to PET. 2,5-Bis(hydroxymethyl)furan (BHMF) is
another interesting bio-based furan monomer, which can be obtained by the reduction
of HMF [102]. Despite the great importance of furan monomers as building blocks
in polymer science, investigation of the possibility of using lipase as catalyst for their
polymerization has been reported just recently. Boeriuet al.reportedlipase-catalyzed
polycondensation of dimethyl furan-2,5-dicarboxylate and linearα,ω-aliphatic diols
with chain length in the range from C2 to C12, under anhydrous conditions provided
by a mixture of anhydrous toluene and tert-butanol of (70:30 wt%), using a one-stage
method [103]. Only a mixture of linear and cyclic furan oligomers, however, could
be obtained under the investigated reaction conditions. Loos and her coworker
could, however, synthesize similar polymer with molecular weight up to 100 kDa by
optimizing the reaction conditions [104]. The authors investigated the N435-catalyzed
polymerization of dimethyl 2,5-furandicarboxylate (DMFDCA) with various renewable
aliphatic diols using two-stage method in diphenyl ether (Figure 7.7).
In another recent study, the authors investigated also the N435-catalyzed polymer-
ization of BHMF with various diacid ethyl esters, that is, diethyl succinate, diethyl
Dimethyl 2,5-furandicarboxylate Aliphatic diol
Two-stage
diphenyl ether Furanic-
aliphatic
polyester
O N435, 80–140 °C
O
O
O O
O
O
O
OOR
n
O + HOROH
Figure 7.7N435-catalyzed polycondensation of dimethyl 2,5-furandicarboxylate and aliphatic diol
using two-stage method in diphenyl ether.
