Towards greener synthesis of sustainable terpene-based monomers for renewable polymers

Project background (identification of the problem and its importance and relevance to sustainability)

Demand for bio-sourced and ideally bio-degradable plastics and polymers is increasing as the governments and the society are making a continuous shift towards a more sustainable future. Broadly, to produce such materials, the four crucial aspects and their environmental impact need to be considered: (i) the source of the feedstock, (ii) the synthetic route towards building blocks, (iii) the conditions for polymer manufacture, and (iv) the usability and performance of newly created materials. The ideal feedstock for building blocks of polymeric materials should be of natural origin (plants), inexpensive and non-food based to avoid the competition with food market. The synthetic route to monomers benefits of being environmentally benign, with mild or recoverable solvents and reagents, and maximized yield and atom economy. Finally, the green polymers obtained should allow for comparable performance and properties with traditional, synthetic polymers, with the simultaneous advantage of being bio-compostable or recyclable/degradable using currently industrially implemented technologies. Terpenes and terpenoids have been recognized as promising natural starting materials for monomer synthesis due to their low cost, by-product nature and intrinsic functionality. Herein, we present the application of simple, green oxidative cleavage chemistry to four selected cyclic, olefinic monoterpenes to synthesise a range of biomass-based monomeric units compatible with the production of sustainable polyamides, polyesters, polycarbonates, and polyurethanes.

Proposed solution and methodology

In this study, our primary aim is to synthesise a range of novel, sustainable monomers from four selected mono and bicyclic olefinic terpenes: a-pinene, 3-carene, a-terpineol and terpinene-4-ol. Once the functionalized monomeric terpenes are obtained, various polymeric materials with tuneable chemical and physical properties might be synthesised. Phase 1 of proposed project aims to convert the chosen alkene terpenoids into 1,6-diols, via oxidative cleavage of oxidized synthons, which have the potential to directly react with natural diacids or the dimethyl esters of natural diacids and produce various polyesters via polycondensation polymerization. Another range of polyesters is going to be accessed via direct oxidative cleavage of olefinic terpenes into difunctional monomeric units (hydroxy acids). Polyamides are to be acquired by transforming 1,6-dicarbonyl intermediates, via reductive amination, into diamines, and subsequent polymerization with a diverse range of natural dicarboxylic acids. Phase 2 of proposed project aims to utilize the synthesised diols and diamines to obtain polyesters with amine moiety incorporated in the structure, and polyurethanes. Polyurethanes can be acquired by reacting terpene-based 1,6-diamines with carbonyldiimidazole, and subsequent reaction of acquired dicarbamides with terpenoic 1,6-diols. Polyesters with embedded amine moiety are of particular interest due to possessing two functional groups capable of breaking down by bacteria in the environment. Terpenoid-based acrylate esters can be acquired by esterification of diols with acrylic acid. The subsequent addition polymerization of aliphatic acrylates with diamines affords the plethora of potentially biodegradable esters.

This CDT will deliver impact aligned to the following agendas:

People
A2P will provide over 60 PhD graduates with the skill sets required to deliver innovative sustainable products and processes into the UK chemicals manufacturing industry. A2P will inspire and develop leaders who will:
- understand the needs of industrial end-users;
- embed sustainability across a range of sectors; and
- catalyse the transition to a more productive and resilient UK economy.

Economy
A2P will promote a step change towards a circular economy that embraces resilience and efficiency in terms of atoms and energy. The benefits of adopting more sustainable design principles and smarter production are clear. For example, the global production of active pharmaceutical ingredients (APIs) has been estimated at 65,000-100,000 tonnes per annum. The scale of associated waste is > 10 million tonnes per annum with a disposal cost of more than £15 billion. Consequently, even a modest efficiency increase by applying new, more sustainable chemical processes would deliver substantial economic savings and environmental wins. A2P will seek and deliver systematic gains across all sectors of the chemicals manufacturing industry. Our goals of providing cross-scale training in chemical sciences with economic and life- cycle awareness will drive uptake of sustainable best practice in UK industry, leading to improved economic competitiveness.

Knowledge
This CDT will deliver significant new knowledge in the development of more sustainable processes and products. It will integrate the philosophy of sustainability with catalysis, synthetic methodology, process engineering, and scale-up. Critical concepts such as energy/resource efficiency, life cycle analysis, recycling, and sustainability metrics will become seamlessly joined to what is considered a 'normal' approach to new molecular products. This knowledge and experience will be shared through publications, conferences and other engagement activities. A2P partners will provide efficient routes to market ensuring the efficient translation and transferal of new technologies is realised, ensuring impact is achieved.

Society
The chemistry-using industries manufacture a rich portfolio of products that are critical in maintaining a high quality of life in the UK. A2P will provide highly trained people and new knowledge to develop smarter, better products, whilst increasing the efficiency and sustainability of chemicals manufacture.
To amplify the impacts of our CDT, effective public engagement and technology transfer will become crucially important. As a general comment, 'sustainability' styled research is often regarded in a positive light by society, however, the science that underpins its effective implementation is often poorly appreciated. The University of Nottingham has developed an effective communication portfolio (with dedicated outreach staff) to tackle this issue. In addition to more traditional routes of scientific communication and dissemination, A2P will develop a portfolio of engagement and outreach activities including blogs, webpages, public outreach events, and contribution of material to our award-winning YouTube channel, www.periodicvideos.com.

A2P will build on our successful Sustainable Chemicals and Processes Industry Forum (SCIF), which will provide entry to networks with a wide range of chemical science end-users (spanning multinationals through to speciality SMEs), policy makers and regulators. We will share new scientific developments and best practice with leaders in these areas, to help realise the full impact of our CDT. Annual showcase events will provide a forum where knowledge may be disseminated to partners, we will broaden these events to include participants from thematically linked CDTs from across the UK, we will build on our track record of delivering hi-impact inter-CDT events with complementary centres hosted by the Universities of Bath and Bristol.