Octahydrofluorenyl rare-earth metal-catalyzed simultaneous chain-growth and step-growth polymerization of para-methoxystyrene

Abstract

The simultaneous chain-growth and step-growth polymerization of p-methoxystyrene was achieved using rare-earth metal complexes (Sc, Y, Gd to Lu) based on an octahydrofluorenyl ligand. As the ionic radius of the metal increased (except for Sc), the polymerization activity of the rare-earth metal catalyst also increased, with a significant difference in the observed rate constants (k_obs = 9.03 × 10⁻⁵ to 1.64 × 10⁻² min⁻¹). In the early stages of polymerization, catalysts with smaller metal ions preferentially formed C–H polyaddition sequences and suppressed the continuous insertion of double bonds in the monomer more effectively. A detailed investigation revealed that the efficient formation of a continuous CC bond insertion sequence through the chain-growth pathway, which is strongly correlated with the ionic radii of rare-earth metal catalysts, significantly influenced the acceleration of polymerization activity. Density functional theory (DFT) calculations indicated that the CC insertion reaction was more kinetically favorable than C–H activation in the initial monomer reaction. Moreover, as the radius of the metal ionic center decreases, the probability of C–H activation increases markedly in the following monomer insertion.