Bio-based polymers are experiencing an explosion of growth, fueled by pressures to move away from traditional petroleum-derived polymer feedstocks. Richard Larock’s group recently published an account of their work with ring-opening metathesis polymerization (ROMP) of vegetable oil-derived monomers, highlighting one role that metathesis can play in the development of such polymers. Larock’s group used both vegetable oils (linseed oil and castor oil) and commercially-available vegetable oil derivatives (Dilulin and ML189, two variations of cyclopentadiene-modified linseed oils) as their feedstocks. The triglycerides were reduced to the corresponding fatty alcohols, and reacted with norbornene dicarboxylic anhydride to form a series of functionalized norbornenes with similar yet distinct characteristics (Scheme 1 – each monomer is a combination of products derived from the three fatty acid chains of the original non-symmetric triglycerides).
The homopolymers of each of these four monomers were obtained by ROMP with 2nd generation Grubbs catalyst, and various mechanistic and mechanical properties of the polymers were explored. The NMCA monomer was far more viscous than the others studied, giving a slower initiating and less complete polymerization. Compared to polyNMSA, polyNMDA and polyNMMA demonstrated more highly-crosslinked polymer structures, resulting in homopolymers with Young’s moduli and tensile strengths comparable to HDPE and polynorbornene.
Biorenewable chemicals offer great opportunities for the future of metathesis, and new metathesis polymers will certainly be one of the highlights of the field.