Fully Renewable Non-Isocyanate Polyurethanes via the Lossen Rearrangement

In this work, a straightforward and efficient synthesis approach to renewable non‐isocyanate polyurethanes (NIPUs) is described. For this purpose, suitable and renewable carbamate monomers, possessing two double bonds, are synthesized from hydroxamic fatty acid derivatives via the Lossen rearrangement in a one‐step synthesis, and sustainable dithiols are synthesized from dialkenes derived from renewable feedstock (i.e., limonene and 1,4‐cyclohexadiene). Subsequently, the comonomers are polymerized with the highly efficient thiol–ene reaction to produce NIPUs with M$_{n}$ values up to 26 kg mol$^{−1}$ bearing thioether linkages. The main side product of the Lossen rearrangement, a symmetric urea, can also be polymerized in the same fashion. Important in the view of sustainability, the monomer mixture can also be used directly, without separation. The obtained polymers are characterized by NMR, attenuated total reflection‐infrared spectroscopy, differential scanning calorimetry, and size exclusion chromatography

Olefin cross-metathesis as a valuable tool for the preparation of renewable polyesters and polyamides from unsaturated fatty acid esters and carbamates

Olefin cross-metathesis of unsaturated fatty acid methyl ester (FAME) derived benzyl carbamates with methyl acrylate is described. The obtained by-product{,} an [small alpha]{,}[small beta]-unsaturated ester{,} was further modified via thia-Michael addition reactions in order to synthesize branched AA-type or AB-type monomers for the preparation of polyesters{,} which are tuneable by oxidation. Cross-metathesis of fatty acid derived carbamates was used as a novel approach to prepare linear AB-type monomers{,} which can be used for the preparation of renewable polyamides PA11{,} PA12 and PA15. The necessary fatty acid carbamates were prepared by applying a catalytic Lossen rearrangement procedure. The presented synthesis strategy has potential for the bio-sourced preparation of monomers for the production of polyamides. All prepared polymers were fully characterized by NMR{,} SEC{,} and DSC analyses. Additionally{,} the Young{\u27}s modulus of the prepared long-chain polyamide PA15 was determined

Regeneration of Cellulose from a Switchable Ionic Liquid: Toward More Sustainable Cellulose Fibers

A CO$_{2}$ switchable solvent system is investigated to find an environmentally friendlier way to produce man‐made cellulose fibers. Cellulose solutions with concentrations from 2 wt% to 8 wt%, based on derivative and non‐derivative dissolution approaches, are investigated. Three different switchable solvent systems are tested. After accessing the stability of the produced cellulose solutions, their regeneration is investigated using different alcoholic coagulation media. In order to find a suitable coagulation medium and stable cellulose solution, a dissolution–regeneration cycle is investigated, while trying to minimize the amount of waste by recovering the employed solvents. The process is optimized and the resulting fibers are characterized by infrared (IR) spectroscopy, optical microscopy, as well as scanning electron microscopy

Olefin cross-metathesis as a valuable tool for the preparation of renewable polyesters and polyamides from unsaturated fatty acid esters and carbamates

Olefin cross-metathesis of unsaturated fatty acid methyl ester (FAME) derived benzyl carbamates with methyl acrylate is described. The obtained by-product{,} an [small alpha]{,}[small beta]-unsaturated ester{,} was further modified via thia-Michael addition reactions in order to synthesize branched AA-type or AB-type monomers for the preparation of polyesters{,} which are tuneable by oxidation. Cross-metathesis of fatty acid derived carbamates was used as a novel approach to prepare linear AB-type monomers{,} which can be used for the preparation of renewable polyamides PA11{,} PA12 and PA15. The necessary fatty acid carbamates were prepared by applying a catalytic Lossen rearrangement procedure. The presented synthesis strategy has potential for the bio-sourced preparation of monomers for the production of polyamides. All prepared polymers were fully characterized by NMR{,} SEC{,} and DSC analyses. Additionally{,} the Young{\u27}s modulus of the prepared long-chain polyamide PA15 was determined

Reactivities and mechanisms in organic reactions involving activation of elemental sulfur under basic conditions

As a readily available and benign waste product of the petrochemical industry, elemental sulfur displays desirable characteristics as a raw material for new processes. Accordingly, the use of elemental sulfur as a reactant or reagent in synthetic organic chemistry receives continuous interest. The implementation of sulfur in synthetic procedures often necessitates the presence of basic or nucleophilic compounds, which are known to serve as activators, enabling a diverse range of transformations. However, the underlying mechanisms are still poorly understood, even for synthetically useful and well-established reactions that have been known for decades. While numerous reviews focus on the various types of products accessible via organic reactions involving elemental sulfur, this manuscript will put its emphasis on common mechanistic steps of these transformations, highlighting and discussing mechanistic studies and postulated pathways

Further Insights into the Catalytic Reduction of Aliphatic Polyesters to Polyethers

The synthesis of medium- and short-chain aliphatic polyethers is industrially limited to the ring-opening polymerization of cyclic ethers with a high ring strain, such as oxiranes, oxetanes, or tetrahydrofuran. This structural limitation can be overcome by the gallium bromide catalyzed reduction of different polyesters into their corresponding polyethers. Herein, the scope of applicable polyesters is broadened, while the influence of the polyester structure on the reduction system is examined. The reactivity as well as side reactions, i.e., overreduction leading to chain cleavage, are shown to depend on the distance of the ester groups in the repeating unit of the polyester. Two different reducing agents, namely triethylsilane and 1,1,3,3-tetramethyldisiloxane, are studied and compared in terms of reactivity and work-up procedures, showing advantages and disadvantages depending on the reduced polyester properties. The reaction conditions are optimized and the reduction can be scaled-up to 60 g polyester. All products are thoroughly characterized

RAFT Polymerization of a Renewable Ricinoleic Acid-Derived Monomer and Subsequent Post-Polymerization Modification via the Biginelli-3-Component Reaction

The search for renewable monomers for radical polymerization techniques is of current interest due to the awareness of sustainability requirements in the chemical sciences. Herein, the synthesis and reversible addition-fragmentation chain-transfer (RAFT) polymerization of a renewable methacrylate monomer based on ricinoleic acid as sustainable starting material is presented. In addition, the hydroxy moiety of the ricinoleic acid is converted to an acetoacetate in order to allow for a post-polymerization modification (PPM) using the Biginelli-three-component reaction (B-3CR), rendering the presented monomer a renewable and highly flexible reactant for the synthesis of polymer materials. Consequently, RAFT polymerization yields macromolecules with a molecular weight of up to 15 000 g mo$^{-1}$l and expectedly narrow molecular weight distributions with Ðs around 1.13. The feasibility of chain extension and block copolymer synthesis is demonstrated. Eventually, the PPM of the acetoacetate moiety of the polymer repeating units using the B-3CR is proven to be efficient with conversions of up to 95% of the acetoacetates, while the modification allows for a pronounced increase of the glass transition temperature to approximately room temperature compared to the unmodified polymers (T$_{g}$ = −50 °C)

Ruthenium Catalyzed Oxidative Cleavage of High Oleic Sunflower Oil: Considerations Regarding the Synthesis of a Fully Biobased Triacid

Tricarboxylic acids are molecules of interest for the synthesis of highly cross-linked polymers, for instance, for the curing of epoxy resins. Herein, a synthesis route to a novel high oleic sunflower oil based triacid is described by applying a ruthenium catalyzed oxidative cleavage of its double bonds. A statistical concept is devised for the prediction of the yields of mono-, di-, and trifunctional derivatives that can be formed from high oleic sunflower oil, depending on the overall conversion of double bonds into this functional group and the overall oleic acid content of the used oil. This concept proved to be highly useful for the explanation of seemingly moderate triacid yields, which are inherently dependent on the unsaturated fatty acid content of the used oil. All obtained sunflower oil based polyacids are fully analyzed by attenuated total reflection infrared spectroscopy (ATR-IR), electrospray ionization mass spectrometry (ESI-MS), $^1$H, $^{13}$C, and quantitative $^{31}$P nuclear magnetic resonance (NMR) spectroscopy. In addition, a more sustainable purification procedure is developed to obtain a polymerizable mixture of polyacids containing more than 2.0 carboxylic acids per molecule in average. Practical applications: Tricarboxylic acids are valuable monomers for the synthesis of cross-linked polymers. The herein reported procedure represents a hitherto unknown synthesis route towards a new triacid and polyacid mixture directly from high oleic sunflower oil