Living Ring-Opening Polymerization of 2-Alkoxy-1-methylenecyclopropanes Initiated by Pd Complexes

Abstract

Pd complexes with a chelating diimine ligand promote ring-opening polymerization of 2-alkoxy-1-methylenecyclopropanes to produce the polymers having vinylidene and alkoxy substituents for every three-carbon unit. 13 C{ 1 H} NMR spectra of the produced polymers show the well-regulated structures with head-to-tail connection of the repeating units. [(π-Allyl)PdCl] 2 initiates living polymerization of 2-alkoxy-1-methylenecyclopropanes (alkoxy: OBu, O t 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 Pd 2 Cl 2 core and two π-allyl−Pd bonds. Treatment of the growing polymer with nucleophilic reagents, such as NaOH/MeOH, NaOH/H 2 O, AgOAc, and NaCMe(COOEt) 2 −PPh 3, cleaves the π-allyl−Pd bonds and forms the polymers having organic functional groups at the terminal. The macromonomer having an α,β-unsaturated aldehyde terminal copolymerizes with styrene in the presence of AIBN to afford the polymer having oligo( 1a ) side chains. Photoirradiation of the polymer of 2-butoxy-1-methylenecyclopropane having the π-allyl−Pd bonds in the presence of chelating N-ligands causes coupling of the π-allylic polymer ends to produce the organic polymer.