Perfluoroarylated Cyclopentadienones: Synthesis, Characterization and Polymerization
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The first chapter of this dissertation reports the synthesis of highly fluorinated Diels-Alder polyphenylenes. The first section of this chapter describes the three-pot synthesis of a perfluoroarylated bis(cyclopentadienone) monomer. The synthesis begins with the previously reported substitution reaction of decafluorobiphenyl and sodium cyclopentadienide. To the resulting 4,4'-octafluorobiphenylene-linked bis(cyclopentadiene), six perfluoro-4-tolyl groups (three on each of the two cyclopentadienyl moieties) are attached by nucleophilic aromatic substitution (SNAr) reactions. The remaining ring methylenes are subjected to a selenium dioxide-catalyzed oxidation to obtain the desired bis(cyclopentadienone) monomer. The next part of this chapter describes the polymerization of the perfluoroarylated bis-(cyclopentadienone) monomer and bis(4-ethynylphenyl) ether. The reaction affords an oligomer (Mn ~ 14,000 g/mol according to size-exclusion chromatographic analysis) that is soluble in several solvents and that decomposes above about 300°C according to thermogravimetric analysis. The second chapter of this dissertation describes a novel method to oxidize per-fluoroarylated cyclopentadiene compounds to the corresponding ketones using catalytic selenium dioxide and stoichiometric hydrogen peroxide. The first part of this chapter shows the synthesis of some perfluoroarylated cyclopentadiene substrates, while the second part of the chapter explores the oxidation of these compounds along with other perfluoroarylated cyclopentadienes already available within our research group. This chapter also explains how the reactivity of the perfluoroarylated cyclopentadienes under the oxidation conditions depends on their structure. Generally more electron-deficient cyclopentadienes react more readily, while sterically crowded cyclopentadienes react more reluctantly. This third chapter of this dissertation describes the synthesis and characterization of a reversible Diels-Alder polymer from an octafluorobiphenylene-linked bis(cyclopentadiene). In the first section, the synthesis of a reversible homopolymer of the bis(cyclopentadiene) monomer is described. The polymer reaches an optimized molecular weight of 11,000 g/mol (degree of polymerization is 20) under the reaction conditions because there is an equilibrium between polymerization and depolymerization even at the mild polymerization temperature (65°C). The TGA trace of the polymer shows that chain degradation takes place beyond 300°C. The thermal reversibility of the polymer was examined by bulk thermolysis, and flash-vacuum thermolysis. The second section describes the synthesis of a methylated bis(cyclopentadiene) that does not undergo self-polymerization at comparatively lower temperature but instead reacts with a second bis(maleimide) monomer. The resulting polymer typically shows a number-average molecular weight of 15,400 g/mol. This polymerization also is limited by the attainment of steady-state end group concentrations. The reversibility of the polymerization is demonstrated by solution thermolysis experiments in which unmasked cyclopentadiene groups are trapped by a monofunctional maleimide.
- Doctoral Dissertations