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A step closer to bio-based secondary diols in polyester synthesis

| By Gerald Ondrey

Isosorbide is a glucose-derived, rigid, secondary diol monomer that can impart favorable mechanical, barrier and thermal properties to condensation polymers, such as polyesters. However, for the past two decades, it has not been possible to synthesize fully bio-based poly (isosorbide succinate) (PIsSu), for example, due to the low reactivity of isosorbide in transesterifications. It was also nearly impossible to arrive at sufficiently long polymer chains (to achieve a certain ductility) while incorporating sufficiently high amounts of isosorbide (to arrive at a strong and durable material).

Now, researchers at the Industrial Sustainable Chemistry group of the University of Amsterdam (the Netherlands; www.uva.nl), led by professor Gert-Jan Gruter, have devised a simple synthesis strategy to overcome the inherently low reactivity of biobased secondary diols. As described in a recent issue of Nature Communications, the researchers overcame the poor reactivity of isosorbide by incorporating an aryl alcohol in the polymerization process. This led to in situ formation of reactive aryl esters and a significant enhancement of the end-group reactivity during polycondensation, the last stage of polyester synthesis when isosorbide’s low reactivity inhibits chain growth in traditional melt polyesterification. As a result, high-molecular-weight materials could be produced with incorporation of high fractions of the bio-based, rigid secondary diol, even up to 100 mol%. For the first time, high-molecular-weight PIsSu could be produced, the polyester obtained from isosorbide and succinic acid. The resulting strong plastics outperform existing plastics like polyethylene terephthalate (PET) in terms of heat resistance, and also show promising barrier and mechanical properties that can outperform common fossil-based materials.

The researchers foresee exploration of previously inaccessible polyester compositions based on monomers with a low reactivity but also the application of similar methods in other classes of polymers, such as polyamides and polycarbonates.

The research was carried out within the RIBIPOL project, funded by the Dutch Research Council NWO with contributions from industry, including The LEGO Group (Billund, Denmark) and Avantium Chemicals B.V (Amsterdam). The toy company supported the project as part of the search for non-fossil alternatives for its plastic bricks, which are currently made of acrylonitrile butadiene styrene (ABS). Avantium is interested in bottle and film applications.