Acetal-Stabilized Carbohydrates as Novel Platform Molecules for Renewable Polymer Production

To address the rising demand for plastics, it is essential to create new types of polymers that are both highly recyclable and emit minimal amounts of greenhouse gases. These plastics should be derived from readily available, renewable feedstocks. Such efforts would supplement ongoing sociopolitical and technological endeavors aimed at increasing the recycling efficiency of current plastic materials. However, the creation of sustainable plastics from abundant renewable feedstocks has been limited by the complexity and efficiency of their production as well as their lack of competitive material properties. To address these challenges, we present a novel approach to produce plastic monomers that are chemically centered around a carbohydrate core. By creating building blocks that incorporate the naturally occurring cyclic structures in biomass, we can efficiently produce chemicals utilizing the principles of green chemistry while simultaneously harnessing the inherent performance advantages of cyclic oxygenates found within the feedstock. The monomer described in this thesis, dimethylglyoxylate xylose (DMGX), can be produced directly from the hemicellulosic fraction of non-edible biomass (wood and agricultural residues) at 83 % yield (95 % from purified xylose), while also enabling the full valorization of the remainder of the biomass (cellulose and lignin). The process is both scalable and straightforward, requiring only the use of a simple aldehyde (glyoxylic acid), an acid, and a solvent. Furthermore, since the only external reactant, glyoxylic acid, is already being produced at a pilot scale from CO2, the potential exists for these products to be entirely derived from non-edible biomass and CO2.The unique properties of this carbohydrate-based monomer, including its rigid, tricyclic, non-planar, and highly polar nature, give rise to desirable characteristics in the resulting polymeric materials. This particular combination of monomeric features produces plastics with high glass transition temperatures, excellent mechanical strengths, and good gas barrier properties, despite being entirely amorphous. Interestingly, the monomer's electron-withdrawing nature appears to reduce the energetic barrier to depolymerization, enabling the creation of chemically recyclable and low-persistence materials. In this thesis, a novel class of polyesters, poly(alkylene xylosediglyoxylates) (PAX), is introduced, which exhibit excellent properties and high degradability. These polyesters can be chemically recycled under mild conditions and can even degrade back to sugars in the presence of water. While these materials are suitable for short-term applications such as packaging, they are likely too degradable for long-term applications, especially in harsh environments. However, when the DMGX monomer is polymerized into polyamides, it produces high performing, durable materials with repeat mechanical recyclability. These polyamides are suitable for long-term use, and have drastically lower associated emissions as compared to the commercial alternatives. Finally, in the last chapter of this thesis, additive engineering is utilized to enhance the durability of the polyesters during high-shear processing, and to adjust the hydrolytic stability of the products to meet target applications. In the conclusion, we then briefly demonstrate the ability to expand the DMGX molecule into a platform of other monomers for use in a wide range of applications.