The carbocationic polymerisation of polyisobutenes initiated by zinc-based Lewis acids has been investigated. Polyisobutenes are important materials that find their applications depending on the molecular weight. Thus, the production of butyl rubber ( Mw ~500,000) by the copolymerisation of isobutene (ill) with isoprene (IP) is an important industrial process. Commercially, polymerisation is initiated by protons generated using an AICh / H20 slurry in chloromethane solvent at low temperatures (ca. -100°C). Incorporation of IP is typically of the order of 1-2%. However, under such conditions isoprene acts as a powerful retardant, and both polymer molecular weight and polymer yield decrease steeply with increasing [IP] in the monomer feed. A system based on Zn(C~5h and an alkyl halide that produces copolymers with high molecular weights and increased isoprene incorporation have been found. Hence with increased main chain unsaturation, which is desirable to achieve more efficient crosslinking and improved compatibility with other unsaturated polymer materials. Studying the reactivity of this Lewis acid we could isolated a non-nucleophilic zincate and proved the capability of generating carbocations. On the other hand, the low reaction rate in covulcanisation found for Butyl rubber could be circumvented by polymerising isobutene with a small fraction of a comonomer different to IP that led to a search for new materials. Hence, polymers containing functionalities such as unsaturations of potentially higher reactivity than internal double bonds, phenylchlorinated units or pendant trimethylsilyl groups have been incorporated into the polymer chain. Finally, a system based on alkylzinc halides and alkyl halides provides polyisobutenes of a wide range of molecular weights ( Mn = 10,000- 150,000) at temperatures between -78 °C and +35 °C. These systems are the first that generates polyisobutenes with high ratios of teoninal double bonds at high temperatures that do not rely on transition metal components or complex noncoordinating anions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:429825 |
| Date | January 2006 |
| Creators | Castillejo, Antonio Guerrero |
| Publisher | University of East Anglia |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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