Chemo- And Stereoselective Polymerization Of Polar Divinyl Monomers By Rare-Earth Complexes

Chemoselective polymerization of divinyl monomers is a promising strategy to access functional polymers via postpolymerization, which however, encounters a cross-linking problem. Herein, we report the coordination polymerization of polar divinyl styrenyl monomers 1-(allyloxy)-4-vinylbenzene (AOS), 1-(but-3-en-1-yloxy)-4-vinylbenzene (BOS), 1-(pent-4-en-1-yloxy)-4-vinylbenzene (POS), and 1-(hex-5-en-1-yloxy)-4-vinylbenzene (HOS) by employing the thiophene-fused cyclopentadienyl scandium bis(alkyl) complexes (2,5-Me-2-3-Ph-6H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (1) and (2,4,5,6-Me-4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (2) and the pyridinyl methylene fluorenyl rare-earth metal complexes (Py-CH2-Flu)Sc(CH2SiMe3)(2) (3) and (Py-CH2-Flu)Y(CH2SiMe3)(2)THF (4). Complexes 1 and 2 show high chemoselectivity for these polar divinyl styrenyl monomers across the styrenyl C=C bond but give atactic products. Catalysts 3 and 4 exhibit solitary chemoselectivity to give atactic poly(AOS) but syndiotactic poly(BOS), poly(POS), and poly(HOS). The copolymerization of the polar divinyl styrenyl monomers with ethylene (E) mediated by 3 exhibits chemoselectivity to afford POS/E and HOS/E copolymers but homopolymer poly(AOS). The reasons behind the (co)polymerization behaviors were investigated by DFT calculation.