Isospecific Polymerization of Halide-and Amino-Substituted Styrenes Using a Bis(phenolate) Titanium Catalyst

Isospecific polymerization of polar styrenes is a challenge of polymer science. Particularly challenging are monomers bearing electron-withdrawing substituents or bulky substituents. Here, we report the coordination polymerization of halide-and amino-functionalized styrenes including para-fluorostyrene (pFS), para-chlorostyrene (pClS), para-bromostyrene (pBrS), and para(N,N-diethylamino)styrene (DMAS) using 2,2^′-sulfur-bridged bis(phenolate) titanium precursor (1). The combination of 1 and [Ph₃C][B(C₆F₅)₄ ] and AlⁱBu₃ provides crystalline poly(pFS)s with perfect isotacticity (mmmm > 95%) and high molecular weights (≤16.0 × 10⁴ g mol⁻¹). Upon activation with a large excess of DMAO, 1 reaches polymerization activity of 5.58 × 10⁵ g mol_Ti⁻¹ h⁻¹ producing isotactic poly(pFS)s featuring higher molecular weights (≤39.6 × 10⁴ g mol⁻¹). The distinguished performance of the 1/DMAO system has been extended to the polymerization of pClS and pBrS, both usually involve halogen abstraction during the polymerization, to produce isotactic and high molecular weight (M_n = 32.2 × 10⁴ vs. 13.7 × 10⁴ g mol⁻¹) polymers in good activities (2.18 × 10⁵ vs. 1.31 × 10⁵ g mol_Ti⁻¹ h⁻¹). Surprisingly, 1/DMAO is nearly inactive for DMAS polymerization, on contrary, the system 1/[Ph₃C][B(C₆F₅)₄ ]/AlⁱBu₃ displays isoselectivity (mmmm > 95%) albeit in a moderate activity.