Ring-opening and acyclic diene metathesis: Polymerisation, thiol click modification and organic-inorganic composite preparation

摘要

Controlled polymerisation techniques have increased the level of structural and chemical sophistication possible in modern synthetic polymers. This has led to advanced properties and applications in fields as diverse as energy production, medicine and electronics. This study aims to further extend the scope of two such techniques, ROMP (ring-opening metathesis polymerisation) and ADMET (acyclic diene metathesis), by combining them with thiol-based click chemistries. An arguable limitation of these polymerisations is their lack of commercially available functional substrates. A nucleophilic thiol-Michael reaction was used to conjugate a library of thiols to an exo-7-oxanorbornene and an α,ω-diene precursor via their acrylic pendants. This allowed the expedient synthesis of 18 novel ROMP monomers and 9 novel ADMET monomers with different polarities, steric characteristics and chemical groups. Homopolymerisation was carried out with Grubbs’ 1st or 3rd generation catalysts, and in the case of ROMP, proceeded in a controlled manner. Low dispersities, the linear evolution of molecular weight and the successful preparation of AB di-block copolymers indicated pseudo-living polymerisation. Due to the gradual coordination and deactivation of Ru-based catalysts with thio-ether moieties, an additional protective oxidation step was required for slower ADMET polymerisations to reach high conversion. Thiol-based chemistries were also employed for post-polymerisation modification. The unsaturated backbone of a representative poly(exo-7-oxanorbornene) was quantitatively modified with 16 functional thiols via radical initiated hydrothiolation without disrupting the well-defined structure of the parent polymer. Monomers bearing latent acrylic ene and trimethylsilane protected alkyne pendants were also synthesised, (co)polymerised and modified with thiol-Michael, thiol-yne, CuAAC and Diels Alder chemistry. Finally, novel organic-inorganic hybrids were prepared via in-situ and simultaneous ROMP and sol-gel processes. Although the hydrophobicity of conventional polynorbornene caused phase separation, well dispersed titania nano-composites were achieved using functional exo-7-oxanorbornene thiol-Michael adducts. The combination of thiol-based click chemistry, metathesis polymerisation and sol-gel condensation was shown to be compatible and highly effective for the preparation of polymeric materials with advanced architectures and tailored chemical functionality.