Aromatic Polymethacrylates from Lignin-Based Feedstock: Synthesis, Thermal Properties, Life-Cycle Assessment and Toxicity.

There is currently a great need for rigid, high-performance and processable bio-based polymers and plastics as alternatives to the fossil-based materials used today. Here, we report on the straightforward synthesis and polymerization of lignin-derived methacrylate monomers based on the methyl esters of syringic, vanillic, and 4-hydroxybenzoic acid, respectively. The corresponding homopolymethacrylates exhibit high glass transition temperatures (Tgs) at 106, 128, and 197 °C, respectively. Rheological properties and thermal stability up to at least 277 °C indicate that these polymers are melt-processable. In addition, copolymers with methyl methacrylate are prepared to further vary and tune the polymer properties. An integrated ex-ante and prospective life-cycle assessment of key environmental impact parameters indicates similar or only slightly higher values compared to well-established fossil-based methyl methacrylate. Moreover, the toxicity towards human HeLa cell lines compares well with that of poly(methyl methacrylate). Hence, the potential availability of lignin-derived acids, combined with the straightforward and potentially upscalable monomer synthesis, make these rigid polymers appealing alternatives towards bio-based high-Tg thermoplastic materials with low toxicity.

Covalent Adaptable Polymethacrylate Networks by Hydrazide Crosslinking Via Isosorbide Levulinate Side Groups.

Reversible crosslinking offers an attractive strategy to modify and improve the properties of polymer materials while concurrently enabling a pathway for chemical recycling. This can, for example, be achieved by incorporating a ketone functionality into the polymer structure to enable post-polymerization crosslinking with dihydrazides. The resulting covalent adaptable network contains acylhydrazone bonds cleavable under acidic conditions, thereby providing reversibility. In the present work, we regioselectively prepare a novel isosorbide monomethacrylate with a pendant levulinoyl group via a two-step biocatalytic synthesis. Subsequently, a series of copolymers with different contents of the levulinic isosorbide monomer and methyl methacrylate are prepared by radical polymerization. Using dihydrazides, these linear copolymers are then crosslinked via reaction with the ketone groups in the levulinic side chains. Compared to the linear prepolymers, the crosslinked networks exhibit enhanced glass transition temperatures and thermal stability, up to 170 and 286 °C, respectively. Moreover, the dynamic covalent acylhydrazone bonds are efficiently and selectively cleaved under acidic conditions to retrieve the linear polymethacrylates. We next show that recovered polymers can again be crosslinked with adipic dihydrazide, thus demonstrating the circularity of the materials. Consequently, we envision that these novel levulinic isosorbide-based dynamic polymethacrylate networks have great potential in the field of recyclable and reusable biobased thermoset polymers.

Chemically Recyclable Poly(ß-thioether ester)s Based on Rigid Spirocyclic Ketal Diols Derived from Citric Acid.

Incorporating rigid cyclic acetal and ketal units into polymer structures is an important strategy toward recyclable high-performance materials from renewable resources. In the present work, citric acid, a widely used platform chemical derived from biomass, has been efficiently converted into di- and tricyclic diketones. Ketalization with glycerol or trimethylolpropane afforded rigid spirodiols, which were obtained as complex mixtures of isomers. After a comprehensive NMR analysis, the spirodiols were converted into the respective di(meth)acrylates and utilized in thiol-ene polymerizations in combination with different dithiols. The resulting poly(ß-thioether ester ketal)s were thermally stable up to 300 °C and showed glass-transition temperatures in a range of -7 to 40 °C, depending on monomer composition. The polymers were stable in aqueous acids and bases, but in a mixture of 1 M aqueous HCl and acetone, the ketal functional groups were cleanly hydrolyzed, opening the pathway for potential chemical recycling of these materials. We envision that these novel bioderived spirodiols have a great potential to become valuable and versatile bio-based building blocks for several different kinds of polymer materials.