| dc.description.abstract | Polymerizations based on olefin metathesis have enabled the synthesis of a large variety of olefin-containing polymers. While numerous studies have shown that the stereochemistry of the alkenes in the polymer backbone has a notable impact on the physical properties of the polymer, the synthesis of stereodefined polymers via olefin metathesis remains a great challenge. Most metathesis catalysts operate under thermodynamic control, which generally favor E (trans) linkages with the main chain connected on opposite sides of the alkenes. Therefore, the properties of polymers with high-cis content are comparatively underexplored due to a scarcity of synthetic methods to access these structures.
Within these polymers, poly(p-phenylene vinylene)s (PPVs), consisting of alternating phenylene and vinylene groups in conjugation, are of special interest. Indeed, the cis/trans configuration of the olefins in the PPV backbone significantly affect its physical properties including optical behavior and solubility. Interestingly, one-way photoisomerization can readily transform olefins in the PPVs backbone from the cis to the trans configuration, rendering PPVs light-responsive. In chapter II and III, we discuss a unique strategy to access all-cis PPVs with living characteristics capitalizing on the polymerization of paracyclophane diene monomers via stereoretentive ring-opening metathesis polymerization (ROMP). Investigation of the kinetics of the polymerization and its living characters is highlighted. Finally, applications to the synthesis of photoresponsive diblock copolymers is presented with an eye towards the construction of intricate, well-defined, and light-responsive polymeric architectures.
While stereoretentive ROMP is as a powerful tool to access cis polymer, the monomer scope is mostly limited to highly strained structures, such as norbornenes and paracyclophane dienes. Additionally, typical ROMP monomers, for example derived from norbornene or cyclooctene, lead to polymers that are challenging to degrade. To overcome these limitations, the development of stereoselective acyclic diene metathesis (ADMET) polymerizations using two families of stereoselective Ru catalysts to deliver a variety of cis polyalkenamers is presented in chapter IV and V. The influence of olefin geometry on the thermal and mechanical properties of the synthesized polymers was investigated through a variety of analytical techniques. | |
