The design and application of functional enyne reagents in metathesis polymerization
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Ring-opening metathesis polymerization (ROMP) using Grubbs-type initiators has become a widespread polymerization technique due to its remarkable functional group tolerance and reliability. This has enabled the synthesis of well-defined materials with applications. However, efficient methods for chain-end modification of ROMP and recycling metal initiators remain significant challenges. The research reported in this thesis explored the design and application of functional enyne reagents to overcome these challenges in ROMP. The key to all of these methods is a terminal alkyne that rapidly reacts with the ruthenium alkylidene and serves as a directing group to promote otherwise inefficient transfer reactions intramolecularly. Using this general relay strategy, different enyne molecules can be designed to give direct polymer-polymer coupling or to generate functional initiators, enabling the functionalization of both ends of the metathesis-derived polymer chain. The enyne derivatives are also capable of recycling the ruthenium catalyst in pulsed-addition ring-opening metathesis polymerization (PA-ROMP) to produce multiple functional chains from single ruthenium initiator with low dispersities. In addition, the terminating type enyne derivatives can be designed as a branching agent, which can be used to synthesize well defined branched ROMP polymers in a convergent synthetic pathway. Overall, the utilities of ROMP for macromolecular construction are widely expanded through these functional enyne reagents and could find broad applications in the design of functional materials.