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

项目背景（识别问题及其重要性和与可持续发展的相关性）随着政府和社会不断向更可持续的未来转变，对生物来源和理想的可生物降解塑料和聚合物的需求正在增加。总的来说，要生产这样的材料，需要考虑四个关键方面及其对环境的影响：(i)原料的来源，（ii）构建模块的合成路线，（iii）聚合物制造的条件，以及（iv）新创造材料的可用性和性能。聚合物材料构建块的理想原料应该是天然来源（植物），价格便宜且非食品为基础，以避免与食品市场竞争。单体合成路线的优点是对环境无害，使用温和或可回收的溶剂和试剂，最大限度地提高了收率和原子经济性。最后，获得的绿色聚合物应具有与传统合成聚合物相当的性能和特性，同时具有生物可堆肥或可回收/可降解的优势，使用当前工业实施的技术。萜烯和萜类化合物由于其低成本、副产物性质和固有的功能性而被认为是很有前途的单体合成天然起始原料。在此，我们提出了简单的绿色氧化裂解化学应用于四种选定的环烯烃单萜，以合成一系列生物质基单体单元，与可持续聚酰胺、聚酯、聚碳酸酯和聚氨酯的生产兼容。在本研究中，我们的主要目标是从四种选定的单环和双环烯烃萜类化合物中合成一系列新的、可持续的单体：a-蒎烯、3-蒈烯、a-松油醇和4-松油醇。一旦得到功能化的单体萜烯，就可以合成各种具有可调化学和物理性质的高分子材料。项目一期旨在通过氧化合子的氧化裂解，将选定的烯烃萜类转化为1,6-二醇，氧化合子有可能与天然二酸或天然二酸的二甲酯直接反应，并通过缩聚聚合生产各种聚酯。另一类聚酯将通过烯烃萜烯直接氧化裂解成双官能单体（羟基酸）而得到。聚酰胺是通过将1,6-二羰基中间体通过还原性胺化转化为二胺，然后与各种天然二羧酸聚合而获得的。拟建项目的第二阶段旨在利用合成的二醇和二胺来获得结构中含有胺部分的聚酯和聚氨酯。聚氨酯可以通过萜烯基1,6-二胺与羰基二咪唑反应，然后得到的二氨基脲与萜烯基1,6-二醇反应。具有嵌入胺部分的聚酯由于具有两种能够在环境中被细菌分解的官能团而受到特别关注。二醇与丙烯酸酯化反应可制得萜类丙烯酸酯。随后的脂肪族丙烯酸酯与二胺的加成聚合提供了大量潜在的可生物降解酯。

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.