Acyclic Diene Metathesis Polymerization Approach for Synthesis of Biobased Polyesters: Summary of Recent Reports

Abstract

Polyester is one of the most common plastics in our daily lives. Biobased chemically recyclable long-chain aliphatic polyesters attract considerable attention in terms of circular economy as a promising alternative to petroleum-based polyethylene as well as polyesters. This mini-review presents recent progress in the synthesis, especially by focusing on the approach using acyclic diene metathesis (ADMET) polymerization. Synthesis of the high molar mass polymers (ca. M_n ≥ 30,000 Da), which exhibit better mechanical (tensile) properties in films, could be achieved from the biobased α,ω-diene monomers, derived from nonedible plant oils and carbohydrate derivatives (such as isosorbide, isomannide, etc.), by using ruthenium–carbene (solvent-free or in ionic liquid, etc.) or molybdenum–alkylidene catalysts. The highly active molybdenum–alkylidene catalyst successfully afforded the polyesters possessing higher M_n values, demonstrating better tensile properties than conventional polyolefins. Moreover, the ADMET approach enables us not only to synthesize a soluble polymer network showing improved tensile strain but also paves the way to the synthesis of multiblock copolymers, modification of the unsaturated backbone using thiol-ene reaction, and preparation of various composites (naturally abundant fibers, etc.). The resultant polyesters could be simply depolymerized by adopting transesterification with ethanol using the CpTiCl₃ catalyst or ethenolysis (olefin metathesis with ethene).

Practical Application: Long-chain aliphatic polyesters (LCAPEs) show enhanced functional properties with efficient chemical recyclability and biodegradability. Plant oils, crude or after subsequent chemical conversion to fatty acids or fatty acid methyl esters, are very valuable renewable feedstocks to prepare LCAPEs. In particular, the flexible unsaturated aliphatic lipidic chains (i.e. 10-undecenoate) derived from castor oil were used extensively with various biobased cores to prepare a plethora of monomers for the synthesis of semicrystalline or amorphous LCAPEs. Various semicrystalline or amorphous polyesters can be prepared using acyclic diene metathesis (ADMET) polymerization to make biobased films, composites, fibers, adhesives, coatings, elastomers, etc. Overall, the prepared biobased polyesters are subtly suited for a wide range of potential applications such as packaging, textile, structural, agriculture, and other crucial applications.