An investigation of the influence of R on the abilities of the polar monomers CH2CH(CH2)8OR (R = Me, PhCH2, Ph3C, Me3Si, Ph3Si) to participate in O- rather than η2-coordination to metallocene alkene polymerizationcatalysts; an unanticipated role for ether oxygen coordination in promotingpolymerization

Abstract

Copolymerization of ethylene and propylene with polar monomers of the types CH₂CH(CH₂)_nOH (n = 1–12) in order to introduce polar functionality into the resulting polymers is possible in principle if the hydroxyl groups of the polar monomers are masked such that they cannot coordinate to Lewis acidic catalyst sites and prevent η²-alkene coordination. Although the use of hydrolysable ethers of the types CH₂CH(CH₂)_nOR (R = alkyl, silyl; n = 1–12) is a protecting group strategy, which has been investigated somewhat, in fact this approach has not been investigated systematically and little is known of the effectiveness of various R groups in hindering oxygen coordination to e.g. metallocene polymerization catalyst systems. We report here the results (a) of an NMR study of reactions of an archetypal metallocene polymerization catalyst, Cp₂ZrMe(μ-Me)B(C₆F₅)₃, with the polar monomers CH₂CH(CH₂)₈OR (R = Me, PhCH₂, Ph₃C, Me₃Si, Ph₃Si), all protected versions of the readily available, long chain polar monomer 9-decen-1-ol, and (b) of an investigation of the copolymerization reactions of these same polar monomers with ethylene and propylene catalyzed by the well known rac-C₂H₄(Ind)₂ZrCl₂/MAO catalyst system. While increasing the steric requirements of the groups R does decrease the apparent abilities of the ethers to displace [BMe(C₆F₅)₃]⁻ from the [Cp₂ZrMe]⁺ cation, there is no correlation of size of R with the degrees of incorporation of the polar monomers into copolymers of ethylene and propylene. Instead, a heretofore unsuspected role for catalyst activation by the ether linkage is suggested.