Synthesis and Kinetic Studies on Palladium Hydride-Initiated Vinyl Polymerisation of Functionalised Norbornenes

Abstract

Chapter I provides a summary of the vinyl polymerisation of norbornenes and their functionalised derivatives, using palladium-based initiators. The concept of photolithography is introduced along with discussion of hexafluoropropanol-(HFP) functionalised norbornene derivatives that provide the basis for the work described in this thesis.
In Chapter II, the synthesis of a series of HFP-functionalised monomers of the type NB(CH2)nC(CF3)2OH (n = 1-2) and NB(CH2)nOCH2C(CF3)2OH (n = 0-6) is described. The monomers prepared differ in the number of methylene units (n) separating the HFP-functionality from the norbornene skeleton, which has previously been shown to have an influence upon polymerisation rate. The series of palladium hydride initiator complexes [Pd(H)(MeCN)(PCy3)2][X] (anion X = BF4, PF6, SbF6, I and B(C6F5)4) were also prepared with a view to determining the effect of the anion on polymerisation rate.
The in-depth study of the stability and reactivity of the discrete complex [PdH(MeCN)(PCy3)2][B(C6F5)4] (Pd1388) is examined in Chapter III. The complex Pd1388 is shown to decompose in chlorinated solvents at 70 °C to form PdCl2(PCy3)2 and two further species, b and c that, despite extensive efforts, could not be identified. Both Pd1388 itself and Pd1388 in its decomposed form (i.e. the mixture of PdCl2(PCy3)2, b and c) are able to act as pro-initiator systems in the polymerisation of exo-NBCH2OCH2C(CF3)2OH (SX1). The kinetics of these polymerisation reactions are explored in detail and a kinetic model is proposed, which accurately describes the overall observed polymerisation rate.
In Chapter IV the kinetic model was extended to the study of pure exo- and pure endo-HFP-functionalised norbornenes, with the model proving to be an excellent fit to experimental data for monomer consumption. An increase in the value of n is shown to produce a corresponding enhancement of polymerisation rate. An examination of the polymerisation of HFP-functionalised norbornenes using GPC as function of time is also described. High molecular weight material is formed at low conversion (<35%) with a reduction in molecular weight observed during the first 30 minutes of the reaction to yield a polymer of peak average molecular weight ~20,000 Daltons and low PDI (<1.4).
In Chapter V, the kinetic model is further extended to the study of mixtures of endo- and exo-HFP-functionalised norbornenes (n = 0-6). As in the case of pure isomers, an increase in the value of n leads to an enhancement in overall polymerisation rate. Finally, the polymerisation of endo-/exo-NBCH2C(CF3)2OH (SXN4) is explored using initiators containing different counter anions (prepared in Chapter II) in order to determine the effect of the anion on polymerisation rate.