Regioselective, stereoselective, and living polymerization of divinyl pyridine monomers using rare earth catalysts

Abstract

The first regioselective, stereoselective, and living polymerization of divinyl pyridine monomers, mediated by simple rare earth catalysts, is reported. The polymerization by Ln(CH₂SiMe₃)₃(L)₂ (Ln = Sc, Y, Lu, Dy; L = THF, Py) is perfectly regioselective for a 2,5-divinylpyridine (DVP) monomer, and the process only concerned the double bond at the 2-position of DVP and the CC bond at the 5-position selectively remained unreacted. In contrast, the polymerization of DVP by La(CH₂SiMe₃)₃(THF)₂ is not regioselective, producing a cross-linking network. The polymerization by Lu(CH₂SiMe₃)₃(Py)₂/B(C₆F₅)₃ is most stereoselective, yielding perfect isotactic PDVP with mmmm >99%. The isoselectivity (mm) of the polymers could be controlled in a range of 31% to 99% by adjusting the amount of THF added. The DVP polymerization is controlled by Lu[CH(C₅H₄N)CH₂CH₂SiMe₃]₃ (formed via in situ mixing of Lu(CH₂SiMe₃)₃(THF)₂ and 2-vinylpyridine), with the molecular weight (M_n) matching the theoretical value of monomer conversion and a narrow dispersity. The stereoblock polymerization of DVP with 2-vinylpyridine was achieved by adding the monomer sequentially. The post-functionalization of stereoblock polymers containing vinyl groups has been achieved by the thiol–ene “click” reaction in which all the CC double bonds are quantitatively converted to thioether bonds.