1,4-Selective Polymerization of 1,3-Cyclohexadiene
and Copolymerization with Styrene by Cationic Half-Sandwich Fluorenyl
Rare Earth Metal Alkyl Catalysts
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Abstract
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(CH<sub>2</sub>SiMe<sub>3</sub>)<sub>2</sub>(THF)<sub>n</sub> (<b>1</b>–<b>10</b>) with an activator
(such as [Ph<sub>3</sub>C][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>A</b>), [PhNHMe<sub>2</sub>][B(C<sub>6</sub>F<sub>5</sub>)<sub>4</sub>] (<b>B</b>), or B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> (<b>C</b>)) and Al<sup><i>i</i></sup>Bu<sub>3</sub>. 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 <i>meta</i>-chloroperoxybenzoic acid (<i>m</i>CPBA) 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
