Olefin Metathesis Polymerization: Overview

Olefin metathesis polymerization applies the olefin metathesis reaction—an exchange of substituents between two olefins in the presence of a catalyst—to synthesize polymers. This method reorganizes substituents on double bonds to create new olefin products. The process enables polymer synthesis compatible with olefins over various other functional groups, making it valuable for producing commercially available polymers like Vestenamer and Norsorex.

The ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a carbon-metal double bond, also known as a carbene. This metal-carbene complex initiates the metathesis reaction and cycles through multiple rounds of catalysis to build polymer chains efficiently.

The Grubbs catalyst undergoes a [2+2] cycloaddition with an alkene to form a four-membered metallacyclobutane intermediate. This intermediate immediately undergoes ring-opening to either regenerate the starting material or break different bonds to form a new carbene and a different alkene product. The new carbene complex then attacks another alkene molecule, repeating the cycle to propagate polymerization.

Ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) are the most widely used methods. ROMP is a chain growth, addition polymerization reaction that opens cyclic monomers. ADMET is a step-growth, condensation polymerization reaction using acyclic dienes. Both methods leverage the olefin metathesis polymerization mechanism to build polymers with distinct growth patterns.

ROMP is a chain growth, addition polymerization that opens cyclic monomers sequentially, building the polymer chain one unit at a time. ADMET is a step-growth, condensation polymerization using acyclic dienes, where monomers couple and release small molecules. While both use olefin metathesis polymerization principles, their growth mechanisms and monomer types differ significantly.

Vestenamer, synthesized by olefin metathesis polymerization, is used for manufacturing rubber objects due to its elastomeric properties. Norsorex, another metathesis-derived polymer, functions as a superabsorbent polymer for oil absorption. These commercially available polymers demonstrate the practical value of olefin metathesis polymerization in producing materials for industrial and consumer applications.

Olefin metathesis polymerization selectively reacts with olefin monomers while tolerating various other functional groups present on the polymer backbone or side chains. This functional group compatibility arises because the Grubbs catalyst specifically targets carbon-carbon double bonds without attacking other reactive groups. This selectivity makes olefin metathesis polymerization advantageous for synthesizing complex polymers with multiple functional groups.