Towards new green polymers: terpene-derived monomers obtained in flow regime.

The current global focus is delivering a more sustainable future. This includes imposing strict mitigation measures on the use of fossil fuels and increasing research investments on development and deployment of alternative renewable energy sources. Even though the use of fossil fuels cannot be currently eliminated considering that it is the largest global source of energy, the recent estimation that the oil, gas and coal reserves may be depleted in the next few centuries has resulted in a crisis in the sector, especially the fate of the future generation. To this end, development and expanding the use of alternative energy sources is highly desirable.

Biomass has been identified as a promising organic carbon source for the production of fuels, polymers and other related materials. This has led to the development of numerous chemical transformation strategies for development of bio-derived building blocks and monomers such as terpene-based polymers. Generally, these polymers are increasingly gained research interest due to their relatively low cost and natural availability in trees, flowers, and fruits. Consequently, these molecules exhibit different structural compositions that require different methods for conversion of terpene-based monomeric units into polymeric materials. Alternatively, several reactions such as Diels-Alder reaction have been developed to enable effective conversion of terpene starting materials into monomeric units. Unfortunately, most of these processes emphasize the specific terpene-derived monomers and polymers.

To this note, Brazilian scientists: Dr. Renan Galaverna, Lucas Fernandes and Dr. Julio Pastre from the University of Campinas together with Dr. Duncan Browne at Cardiff University in Wales developed a continuous flow processing method for the synthesis of monomers for the synthesis of green polymers. In particular, the continuous processing technique was used to synthesize two terpene-derived monomer libraries. The work is currently published in the research journal, Reaction Chemistry and Engineering.

Briefly, research team started their work by developing the continuous flow process for the preparation of the monomer libraries derived from renewable terpene feedstocks. Next, the library base comprised of small terpene range such as ocimene and myrcene. The first library was derived from a Diels-Alder reaction while the second library was derived from exhaustive hydrogenation of alkenes present in the first library by the help of tube-in-tube reactor (AF-2400) and Pd/C catalyst. Eventually, a Diels-Alder process was used to evaluate the scaling of the two libraries.

The use of continuous flow processing was more advantageous as compared to the conventional batch procedure. For instance, it offered large scale processing due to precise control of the reaction parameters and other factors such as higher surface area and improved heat and mass transfer. Additionally, they confirmed the scale-up potential for both libraries using Diels-Alder reaction and hydrogenation process. The former delivered 10.5 grams after 3 hours while the later delivered 10.5 grams after 16 hours.

In summary, the research team successfully developed and demonstrated the use of a continuous flow process for generating terpene-derived monomer libraries. It is worth noting the described process is capable of delivering multiple grams of monomer units without the use of loading loops. Considering the high productivity of the continuous flow process, the study by Dr. Julio Pastre and his colleagues will pave way for the synthesis of polymers derived from monomers with bicyclic rings for enhanced mechanical properties.