Taking advantage of the structural diversity of different biomass resources, recent efforts were directed towards the synthesis of renewable monomers and polymers, either for the substitution of petroleum-based resources or for the design of novel polymers. Not only the use of biomass, but also the development of sustainable chemical approaches is a crucial aspect for the production of sustainable materials. This review discusses the recent examples of chemical modifications and polymerizations of abundant biomass resources with a clear focus on the sustainability of the described processes. Topics such as synthetic methodology, catalysis, and development of new solvent systems or greener alternative reagents are addressed. The chemistry of vegetable oil derivatives, terpenes, lignin, carbohydrates, and sugar-based platform chemicals was selected to highlight the trends in the active field of a sustainable use of renewable resources.
Herein, a novel approach is reported for the synthesis of medium- and long-chain aliphatic polyethers 2 based on the GaBr -catalysed reduction of polyesters 1 with TMDS as the reducing agent. Thus, various linear and branched aliphatic polyesters 1 were prepared and systematically investigated for this reduction strategy, demonstrating the applicability and versatility of this new polyether synthesis protocol. Medium- and long-chain chain polyethers were obtained from the respective polyesters without or with minor chain degradation, whereas short-chain polyesters, such as poly-l-lactide 1 i and poly[(R)-3-hydroxybutanoate] 1 j, showed major chain degradation. In this way, previously unavailable and uncommon polyethers were obtained and studied.
An efficient synthesis strategy for the preparation of two renewable polyesters and one renewable polyamide via catalytic oxyfunctionalization of methyl 10‐undecenoate, a castor oil derived platform chemical, is described. The keto‐fatty acid methyl ester (keto‐FAME) is synthesized applying a cocatalyst‐free Wacker oxidation process using a high‐pressure reactor system. For this purpose, catalytic amounts of palladium chloride are used in the presence of a dimethylacetamide/water mixture and molecular oxygen as sole reoxidant. The thus derived AB monomers (hydroxy‐esters, amine‐ester) are synthesized from the obtained keto‐FAME through Baeyer–Villiger oxidation and subsequent transesterification, reduction, or reductive amination, respectively. The resulting AB step‐growth monomers are then studied in homopolymerizations using 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene, DBU, and titanium(IV) isopropoxide as transesterification catalyst, yielding polymers with molecular weights (Mn) up to 15 kDa. The polyesters and the polyamide are carefully characterized by FTIR, SEC, 1H‐NMR spectroscopy, and differential scanning calorimetry analysis.
Two synthetic approaches to functionalize plant oil derived platform chemicals were investigated. For this purpose, methyl 10‐undecenoate, which can be obtained by pyrolysis of castor oil, was used in olefin cross‐metathesis under neat conditions forming an unsaturated α,ω‐acetoxy ester. A catalyst screening with 11 different ruthenium‐based metathesis catalysts was performed, revealing that well‐suited catalysts allow for full conversion and very good cross‐metathesis selectivity at a loading of only 0.5 mol%. An alternative possibility to the aforementioned synthetic method is a palladium‐catalyzed reaction of methyl 10‐undecenoate with acetic acid in the presence of dimethyl sulfoxide. Here, the formation of linear and branched unsaturated acetoxy esters as well as a ketone was observed. The conversion as well as the selectivity of this procedure was studied under different reaction conditions and compared to the cross‐metathesis results. Based on the successful functionalization of methyl 10‐undecenoate, methyl oleate was investigated in this palladium‐catalyzed CH activation reaction. Due to the lower reactivity of the internal double bond the desired acetoxy ester was only obtained in moderate conversion in this case. In summary, this study clearly shows that palladium‐catalyzed functionalization of unsaturated fatty compounds via CH activation is an attractive alternative to the well‐established olefin cross‐metathesis procedure.
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