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

Abstract

Nitrile-ligated copper(II) and zinc(II) complexes comprising (fluoroalkoxy)aluminates as weakly coordinating anions (WCAs) have been synthesized and applied for the polymerization of isobutylene at room temperature (30 C). The polymers obtained are in the low and moderate molecular weight range and show characteristics of the highly reactive polyisobutylene. Results indicate that the fluoroalkoxy aluminate WCAs have even a higher tolerance toward water in IB polymerization than the earlier tested perfluoroborate WCAs. Studies showed that water plays an important role in the polymerization process, which indicates a polymerization mechanism similar to a proton-initiated carbocation polymerization. The role of the WCAs and their importance for the room-temperature polymerization process was re-examined, and the effect of the addition of proton and electron donors including proton traps (2,6-di-tert-butyl-4-methylpyridine or DTBP) was studied in detail. The polymerization reaction seems to be dominated by transfer reactions that lead to the high content of exo double bonds while propagation proceeds via conventional cationic polymerization.

Cationic polymerization of isobutylene at room temperature

“…Recently, it was also demonstrated that the copper (II) and zinc (II) complexes associated with the perfluoroalkoxyaluminates, in particular the [Al(OC(CF 3 ) 3 ) 4 ] − counteranion as shown in Figure 3(WCA 4), can also be applied for the polymerization of IB at 30 °C 47. Similar results were obtained with the perfluoroalkoxyaluminates as with the perfluoroborate WCAs.…”

“…As already indicated, in the recent years new polymerization strategies have appeared for the preparation of PIB, which are based on initiator or metal complex systems associated with weakly coordinating anions (WCAs) 34–47…”

“… Structures of the nitrile‐ligated metal cations and perfluoroborate (1–3) and perfluoroalkoxyaluminates (4) WCAs applied for the polymerization of IB. (R = CH 3 or C 6 H 5 and M = corresponding metal center) 34–47…”

“…In addition, very recently, also the WCAs have been further varied by applying aluminate structures (Fig. 3, WCA 4) associated with nitrile‐ligated Cu (II) and Zn (II) allowing also the preparation of HR PIB at RT in high yields within 2 h of reaction 47…”

Catalytic chain transfer polymerization of isobutylene: The role of nucleophilic impurities

“…The exo‐olefin terminated PIB is also referred to as “highly reactive” PIB (HR PIB), since it readily reacts with maleic anhydride in a thermal “ene” reaction to produce PIB succinic anhydride that can be converted to polyisobutenylsuccinimide, used as ashless dispersants. In the recent years, several research groups have reported on new catalyst systems for the synthesis of HR PIB . Some major drawbacks for the new HR PIB process systems include low process temperatures and/or use of polar chlorinated solvents that present serious limitations for industrial application .…”