From melt- to solid-stage polycondensation: how to revolutionize the design of sustainable polymers with advanced properties

Environmental and economic concerns, associated with the mismanagement of petroleum-based plastics waste are pushing both University and Industry efforts to the introduction of cleaner sustainable technologies. The highest priorities are methods avoiding the use of polluting and unsafe volatile solvents/chemicals; and allowing the facile replacement of the petrol-based monomers by monomers issued from annually renewable resources. With this respect, the polycondensation – a step-growth polymerization - is being attracted much attention. Polycondensation is widely used in Nature, being the main synthetic platform for natural polymers such as proteins and cellulose. In our man-made technology, the process plays an important role in the synthesis of commodity and technical polyesters and polyamides - versatile classes of polymers covering large applications going from fibers to high-performance polymers, thermoplastics and elastomers. However, despite its green aspect, polycondensation is often complicated by its slow rate and side reactions, resulting in low molecular weight and yield of the polycondensation polymer, including the lack of functionalities.
Hence the lecture will highlight the benefits of using combined melt-polycondensation to other synthetic procedures as chain-coupling or “click” reactions in order to tailor the properties of the functional (co)polyesters , . The results have shown that such combined/copolycondensation can be used as a green method to design sustainable plastics going from reinforcing agents to dispersants and curable coatings. To extend the range of functional polymers, the solid-state modification (SSM) from batch into a continuous process by reactive extrusion (REx) will be discussed as well. It represents an easy-to-use and solvent-free tool as it only affects the amorphous part of the polymer, thus preserving its initial mechanical properties while enhancing its recyclability extent5,6. It simply consists in heating the starting semi-crystalline polymer together with a (co)monomer within a temperature range between the glass transition temperature (Tg) and the melting temperature (Tm) in an inert atmosphere or under vacuum and can be implemented in a (semi)continuous manner7,8. It results polymers of improved characteristics upon the (co)monomer used, while preserving the mechanical and thermal properties of the initial polymer. Poly(butylene terephthalate) (PBT) and 1,12-dodecanediol (DDO) are used as model compounds. This last study encompasses the design of a new process for recycling polymeric materials and offers the possibility of making polymers more sustainable and recyclable.