1,4-Selective polymerization of 1,3-cyclohexadiene and copolymerization with styrene by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts

The regioselective coordination-insertion polymerization of 1,3-cyclohexadiene (CHD) and copolymerization with styrene (S) could be achieved by cationic half-sandwich fluorenyl rare earth metal alkyl catalysts generated by treating half-sandwich fluorenyl rare earth metal dialkyl complexes Flu'Ln(CH₂SiMe₃)₂(THF)_n (1-10) with an activator (such as [Ph₃C][B(C₆F₅)₄] (A), [PhNHMe₂][B(C₆F₅)₄] (B), or B(C₆F₅)₃ (C)) and AlⁱBu₃. The homopolymerization of CHD afforded poly(CHD)s with complete 1,4 selectivity (1,4 selectivity up to 100%). The copolymerization of CHD with styrene gave new random CHD-S copolymers with CHD content ranging from 22 to 74 mol % containing 1,4-linked CHD-CHD, alternating CHD-S, and syndiotactic S-S sequences unavailable previously. The activity of the copolymerization and the comonomer compositions and sequences of the resulting CHD-S copolymers could be easily controlled by changing the substituted fluorenyl ligand, the metal center, the activator, the temperature, and the molar ratio of comonomers. The residual C-C double bonds of the random CHD-S copolymers could be further epoxidized by meta-chloroperoxybenzoic acid (mCPBA) at room temperature to prepare high-performance polymers with polar groups and reactive sites in the polymer backbone. Such functionalization could improve the solubility, dying, acidity, and surfactivity of these copolymer materials.