Stereoselective Copolymerization of Unprotected Polar and Nonpolar Stryenes by an Yttrium Precursor:Control of Polar-Group Distribution and Mechanism

摘要

Styrene underwent unprecedented coordinationinsertion copolymerization with naked polar monomers (ortho-/ meta-/ para-methoxystyrene) in the presence of a pyridyl methylene fluorenyl yttrium catalyst. High activity (1.26 X 10(6) gmol(Y)(- 1)h (-1)) and excellent syndioselectivity were observed, and high-molecular-weight copolymers (24.6 X 10(4) gmol (-1)) were obtained. The insertion rate of the polar monomers could be adjusted in the full range of 0-100 simply by changing the loading of the polar styrene monomer. Strikingly, the copolymers had tapered, gradient, and even random sequence distributions, depending on the position of the polar methoxy group on the phenyl ring and thus on its mode of coordination to the active metal center, as shown by tracking the polymerization process and DFT calculations.