Syndiospecific Polymerization of o-Methoxystyrene and Its Silyloxy or Fluorine-Substituted Derivatives by HNC-Ligated Scandium Catalysts: Synthesis of Ultrahigh-Molecular-Weight Functionalized Polymers

A scandium dication active species [(IPr)Sc(mu-CH2SiMe3)(mu-CH2CHMe2)(AlBu2)-Bu-i](2)+ [B(C6F5)(4)](2)(-) (IPr = (2,6-(C6H3Pr2NCH)-Pr-i)(2)C) in situ generated from the reaction of an N-heterocyclic carbene-ligated scandium trialkyl complex (IPr)Sc(CH2SiMe3)(3) (2) with 1-3 equiv of cocatalyst [Ph3C] [B(C6F5)(4)] and an excess of Al(i)Su(3) exhibits unprecedentedly high activity (up to 2.2 x 10(6) g.mol(Sc)(-1).h(-1)) and syndiotactic selectivity (rrrr > 99%) in the polymerization of o-methoxystyrene (oMOS) and its silyloxy- or fluorine-substituted derivatives, affording syndiotactic poly(oMOS)s and their silyloxy or fluorine-substituted derivatives with ultrahigh molecular weight (M-n up to 4.6 x 10(6)) and moderate molecular weight distributions (M-w/M-n = 1.37-2.21) unavailable by the traditional catalysts. Based on in situ NMR spectroscopy, matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) spectroscopy, and density functional theory (DFT) calculations, a plausible coordination polymerization mechanism has been proposed for the syndiotactic polymerization of oMOS by such a Sc dication active species.

Automated summary

A scandium dication active species exhibits unprecedentedly high activity and syndiotactic selectivity in the polymerization of o-methoxystyrene, producing syndiotactic poly(oMOS)s with ultrahigh molecular weight not achievable by traditional catalysts.