Noncoordinating anions in carbocationic polymerization

Abstract

The initiation and catalysis of isobutylene polymerization from several new metallocene and nonmetallocene initiator‐catalysts that contain the noncoordinating anions (NCA), B(C6F5)4− and RB(C6F6)3−, is reported. Application of these initiator‐catalysts is extended to styrenics and vinyl ethers. The NCA does not contribute to termination and can be used in low concentrations compared with conventional Lewis acids. These qualities provide for isobutylene polymerizations that yield low Mn oligomers or high Mn polymer, dependent upon the initiator and polymerization conditions. Mechanistic aspects of initiation, transfer and termination as well as the participation of adventitious water are considered for each class of initiator‐catalyst. The influence of the NCA on the stereoregularity of cationic styrene polymerization is also considered. NCAs do not cause the stereospecific carbocationic polymerization of styrene. We suggest that under conditions not conducive to carbocationic polymerization, NCA/metallocenes mediate the coordination polymerization of styrene. © 1997 John Wiley & Sons, Inc.

The role of solvent‐ligated metal(II) complexes incorporating (fluoroalkoxy)aluminates as weakly coordinating anions in isobutylene polymerization

“…Our observations and postulates are in accordance with earlier discussions by Shaffer and Ashbaugh15 and Bochmann and coworkers48 on the role of water in IB polymerization applying WCA‐related complexes, albeit at low temperature. Shaffer and Ashbaugh suggested two mechanisms, one based on the hydration of the catalyst and the other based on the transfer reactions involving the interaction of the excess water with the growing chain.…”

Cationic half‐sandwich scandium complex for the synthesis of polyisobutylene with high molecular weight under mild conditions

“…It proved that [Cp′ScR 2 THF]/[Ph 3 C][B(C 6 F 5 ) 4 ] initiator system in cationic polymerizations has high activity and can suppress the chain transfer side reaction at mild condition, because of extremely low proton affinities of boride counteranions that steadies cationic pairs at elevated temperatures. Meanwhile, the M n of polyisobutylene increased obviously with reducing polymerization temperature, which is consistent with the restraining isomerization of growing macrocations illustrated in other initiator systems …”

Polymerization of Isobutylene and the Copolymerization of Isobutylene and Isoprene Initiated by the Metallocene Derivative Cp*TiMe2(μ-Me)B(C6F5)3

“…Low-molecular-weight samples of PIB (M n 960-3400) were therefore obtained in CH 2 Cl 2 at -50 °C by initiation with Cp*TiMe 2 (µ-Me)B(C 6 F 5 ) 3 followed by immediate termination with methanol. We show in Figure 2 the structural features anticipated for PIB formed via carbocationic processes and the approximate 1 H and 13 C chemical shifts reported previously in the literature, 8,9 and in Table 2 the chemical shifts and assignments of all resonances observed here.…”