230 Introduction to Renewable Biomaterials
glutarate, diethyl adipate, and diethyl sebacate (98+%), using three-stage method [105].
Only polyester withMwin the range of 1800–2900 could be obtained, which was
explained by the observed etherification side reaction.
7.4.5 Conclusions and Remarks
Enzyme-catalyzed polymerization has been revealed to be a green metal-free synthetic
route to prepare polyesters from renewable materials under mild conditions in a
relatively short time. Enzymes also allow the production of clean and attractive reactive
polyesters, with double bond, OH, epoxy groups, in one step, which can be used later
in many interesting applications.
It should be stressed finally that, while the sustainability is a mankind’s dream, the
current achievements in polymer field still fall below the expectations of this dream.
Although the current statistics indicates clearly that the bio-based share grows in a faster
rate than the growth of global polymer market [1], the recent drop in oil price could,
however, reduce this growth. On the other hand, despite the aforementioned advantages
of using lipase for polyester synthesis, the enzymes are used yet for industrial production
of polyesters due to some obstacles such as (i) the large quantity of enzymes required
for the polymerization process, which increases significantly the production cost, (ii)
relatively limit the number of polymers with high molar mass, which can be obtained
using this polymerization technique, (iii) and the low reactivity of lipases toward some
important commercially available monomers, for example, lactides [13, 106]. Therefore,
significant scientific efforts should be made in order to overcome these critical difficul-
ties to make our planet livable for our children and grandchildren.
7.4.6 Questions for Further Consideration
- How can we increase the efficiency of lipases toward enzymatic polymerization?
- How can we increase the temperature tolerance of lipases?
- What should be done in order to increase the regioselectivity of enzymes at
temperatures higher than 50∘C?
- Which strategies should be followed to increase the molar mass of polyesters
produced via enzymatic polymerization?
- How can we reduce the cost of polymer production when enzymes are used as
catalyst?
List of Abbreviations
PLA poly(lactic acid)
PBS poly(butylene succinate)
γ-BL γ-butyrolactone
γ-VL γ-valerolactone
LA levulinic acid
DVL δ-valerolactone
ε-CP ε-caprolactone
HMF hydroxymethylfurfural/(hydroxymethyl) furfural
ROP ring-opening polymerization
