Zirconium-Catalyzed Polymerization of a Styrene: Catalyst Reactivation Mechanisms Using Alkenes and Dihydrogen

Abstract

Zirconium salicylaldiminates in the presence of Al i Bu 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] are inactive for the homopolymerization of p-tertbutylstyrene (TBS), but the addition of hexene leads to a highly active system. Analysis of the polymers by NMR and MALDI indicates surprisingly that most of the product chains contain no hexene, while some contain a single hexene unit. Addition of dihydrogen also leads to the production of poly(TBS) without substantial reduction in molecular weight and with main-chain endgroup unsaturation. These and other observations lead us to two related mechanisms for the hexene-and dihydrogen-promoted reactions. Synthetic and catalytic studies indicate that the active species is not a typical bis(salicylaldiminato) compound but an amido/alkoxido system. An authentic compound of this class is highly active for the TBS polymerization even in the absence of added aluminum alkyl.

Homopolymerization of styrenic monomers and their copolymerization with ethylene using group 4 non‐metallocene catalysts

“…The inferior activity of the zirconium catalysts compared to their titanium counterparts in styrene polymerization was observed earlier and it was proposed that the differences in their performances were caused by the larger radius and lower electrophilicity of zirconium. [37,46,47] The same relation was found for the second activator, MMAO (run S1 vs. S7). However, under the same polymerization conditions both the catalytic systems based on MMAO exhibited lower polymerization activities than did the systems with the borate compound.…”

“…[36] Interestingly, the zirconium salicylaldiminate based catalysts, which are inactive in homopolymerization of p-tertbutylstyrene, can be activated by the addition of 1-hexene which awakens the benzylic dormant state by β-hydrogen transfer to the monomer. [37] The same procedure proved ineffective for styrene polymerization.…”