CoCaBio: synthesis of bio-based polymers via organocatalysis
The CoCaBio project (ring-opening co-polymerization of succinic anhydride derivatives and bio-based epoxides via organocatalysis) aims to synthesize polyesters from renewable resources, using organic catalysts. In the future, this approach could potentially lead to the discovery of new materials which have microstructures with scalable properties. This work is shared between the team of Franck Le Bideau at the Biomolecules: Design, Isolation, Synthesis laboratory (BioCIS - Univ. Paris-Saclay, CNRS, Univ. Cergy Pontoise) and that of Samuel Dagorne at the Institute of Chemistry in Strasbourg.
The omnipresence of plastics in our daily lives, and our dependence on them for all our uses, poses countless problems. In addition to the environmental pollution caused by these materials, the use of fossil fuels in their manufacture now means we need to find new synthesis methods which are more in line with sustainable development. Indeed, plastics are polymers, i.e. large-scale assemblies of small molecules derived mainly from oil and obtained artificially by chemical synthesis. In a bid to move away from oil, a new approach is exploring the use of renewable polymers. This is the aim of the CoCaBio project (ring-opening co-polymerization of succinic anhydride derivatives and bio-based epoxides via organocatalysis). Led by the teams of Franck Le Bideau, an expert in organocatalysis applied to the Michael reaction, and Samuel Dagorne, a specialist in ring-opening polymerization, the project started in 2019 and is funded by the French National Research Agency (ANR).
The benefits and limits of petrochemistry
In the early 20th century, human productivity began to increase exponentially. Demand for consumer goods made from non-renewable resources was exploding, and oil-based thermoplastics were riding high. Polyesters were among the most popular polymers. These macromolecules contained the ester function -(C=O)-O- in their main chain. "They're known for their many applications, such as PET," says Franck Le Bideau.
Polyethylene terephthalate (PET), patented in 1941 by British chemists John Rex Whinfield and James Tennant Dickson, and acquired by the American Du Pont de Nemours group in 1945, is a highly sought-after thermoplastic with good gas barrier properties and high chemical resistance. It is found in the form of synthetic fibres in clothing (60% of current plastic production), but also in plastic bottles and other food packaging (30%).
While 8% of today's oil production is dedicated to plastic production (4% for raw materials and 4% for the energy required to manufacture them), the use of products made from fossil resources is faced with two major global problems: environmental pollution and the scarcity of these same resources. Their depletion, intensified by growing global demand, means that new deposits must be found that are less profitable due to their nature or inaccessibility.
Furthermore, a major drawback of current polymer production lies in the use of rare and/or costly and/or toxic metal catalysts, which considerably limits their applications, particularly in the fields of food packaging or medicine.
The rise of organocatalysis and the aims of the CoCaBio project
Against this backdrop, the need for polymers of renewable origin, which today accounts for less than 1% of the world's total polymer production, is set to rise sharply in the years ahead. These future developments will be based on the production of bio-based molecules, chemical compounds derived entirely from biomass (i.e. of biological origin, excluding fossil carbon sources). Organic catalysts have been enjoying renewed interest since the early 2000s. In 2021, Germany's Benjamin List, a professor at the Max Planck Institute, and Britain's David MacMillan, a professor at Princeton University, were awarded the Nobel Prize in Chemistry for their work on so-called asymmetric organocatalysis.
"Unfortunately, the organocatalytic approach to polyester synthesis has not been greatly explored to date," regrets Franck Le Bideau. "However, in the short term, it will be complementary, before becoming a long-term eco-compatible replacement for current catalytic methods." This is the gamble being taken by the CoCaBio project, launched in September 2019 for 48 months, with €348,000 in ANR funding. "For us, this money was used to finance the running of the laboratory and the post-doctoral recruitment of Dmytro Ryzhakov. In Strasbourg, Gaël Printz has just defended his thesis on the subject," explains Franck Le Bideau. As for the project itself, it will continue until March 2024 due to the delay caused by the health crises.
The initial aim of the CoCaBio project was to form polymers from two renewable monomers. On the one hand, a succinic anhydride derivative - (CH2CO)2O - derived from the dehydration of succinic acid, itself extracted from succin (or Baltic amber). On the other, an epoxide, i.e. a chemical substance consisting of an oxygen on top of a single C-C bond. The whole process had to be broken down into several stages. Initially, scientists had to obtain organocatalysts supposed to avoid the use of metal catalysts. Secondly, the teams had to synthesize epoxides by oxidizing various molecules of renewable origin - sugars, polyunsaturated fatty acids, geraniol (a rose-scented alcohol found in essential oils). Next, the Michael reaction, in which a carbanion (negatively charged ion) is added to an aldehyde or ketone, was to lead to succinic anhydride derivatives. Finally, the experiment had to be realised with the co-polymerization of a derivative and an epoxide by opening their cycles, and obtaining new materials to characterise.
Less efficient catalysis and new avenues to explore
After four years of research, Franck Le Bideau takes stock of the results finally obtained from the CoCaBio project. "The Michael reaction, which we had in mind to obtain succinic anhydride derivatives, didn't work," he recalls. So he and his team changed tack and synthesized derivatives from aspartic acid, obtained from asparagine, itself isolated from asparagus juice. "In terms of the epoxides, we have formed some from bio-based molecules such as eugenol, which is extracted from cloves," summarises the researcher. Finally, some polyesters were obtained by co-polymerization using organocatalysts such as thioureas, which are sulphur derivatives of urea. Unfortunately, however, these have proved less effective than conventional metal catalysts.
"It's never easy to embark on a field that's still so unexplored. However, during the course of our work, we have obtained encouraging preliminary results with a new type of organocatalyst. We have also synthesized polyethers, in other words, polymers synthesized from epoxides alone, which have interesting properties," announces Franck Le Bideau. “Now that we've done the groundwork, we have several avenues to follow in the months ahead."
- Dmytro Ryzhakov, Gaël Printz, Béatrice Jacques, Samir Messaoudi, Françoise Dumas, Samuel Dagorne and Franck Le Bideau. Organo-catalyzed/initiated ring opening co-polymerization of cyclic anhydrides and epoxides: an emerging story. Polym. Chem., 2021,12, 2932-2946.