Isolation of ROMP-Generated Macrocyclic Polyalkenamers via Polar Monomer Incorporation and Chain-End Modification

Macrocyclic polyalkenamers formed as byproducts during ring-opening metathesis polymerization (ROMP) provide valuable insight into ring-chain equilibria and secondary metathesis processes. However, the characterization of these macrocycles is often complicated by the presence of linear polymer products with identical chemical composition. Here, we present a strategy to facilitate the isolation of macrocycles generated during ROMP by modifying chain ends using enyne metathesis chemistry and introducing polar functional groups into linear polymer chains through the addition of polar monomers. The resulting polarity difference allows nonpolar macrocycles to be separated from linear polymers by using conventional silica gel chromatography. The isolated cyclic fractions were characterized by gel permeation chromatography (GPC), NMR spectroscopy, and matrix-assisted laser desorption-ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using this approach, we systematically investigated how reaction parameters influence the yield and molecular weight of macrocycles in the ROMP of cyclooctadiene (COD). The methodology also enables comparative analysis of macrocycle formation in the ROMP of cyclooctene (COE), cyclopentene (CP), and norbornene (NB). These results provide a separation-based approach for studying the macrocyclic species formed during ROMP.