Living ring-opening polymerization of 2-alkoxy-1-methylenecyclopropanes initiated by Pd complexes

Pd complexes with a chelating diimine ligand promote ring-opening polymerization of 2-alkoxyl-1-methylenecyclopropanes to produce the polymers having vinylidene and alkoxy substituents for every three-carbon unit. C-13{H-1} NMR spectra of the produced polymers show the well-regulated structures with head-to-tail connection of the repeating units. [(pi-Allyl)PdCl](2) initiates living polymerization of 2-alkoxy-1-methylenecyclopropanes (alkoxy: OBu, O'Bu, OMe) to afford the polymers with narrow molecular weight distribution. Molecular weight of the polymer was controlled over a wide range by changing the initial monomer-to-initiator molar ratio. Direct measurement of the growing polymer of 2-butoxy-1-methylenecyclopropane by NMR and GPC indicates that the polymer molecule has a dimer structure with a Pd2Cl2 core and two pi-allyl-Pd bonds. Treatment of the growing polymer with nucleophilic reagents, such as NaOH/MeOH, NaOH/H2O, AgOAc, and NaCMe(COOEt)(2)-PPh3, cleaves the pi-allyl-Pd bonds and forms the polymers having organic functional groups at the terminal. The macromonoiner having an alpha,beta-unsaturated aldehyde terminal copolyinerizes with styrene in the presence of AIBN to afford the polymer having oligo(la) side chains. Photoirradiation of the polymer of 2-butoxy-1-methylenecyclopropane having the pi-allyi-Pd bonds in the presence of chelating N-ligands causes coupling of the T-allylic polymer ends to produce the organic polymer.