These catalytic metal complexes can initiate the synthesis of polymers with unique cyclic topologies. Only a few techniques are available to create cyclic polymers. A common synthesis route involves intramolecular coupling of polymer chain ends. However, this route has inherent limitations in that it requires dilute conditions and long reaction times. Ring closing synthesis attempts to produce samples of unique ring-shaped polymers, yet it is difficult to product at a large scale.
Researchers at the University of Florida have developed compounds known as metallacyclopentadienes for initiating polymerization of alkynes to produce cyclic polymers efficiently and on large scales for the first time. These catalytic intermediates apply ring expansion metathesis polymerization (REMP) to speed up the reaction time and allow the polymers to have new physical properties.
Metal complexes that polymerize alkynes by ring expansion metathesis polymerization (REMP) to yield cyclic polyalkenes. Subsequent hydrogenation provides the corresponding cyclic version of cyclic polyolefins.
These metallacyclopentadiene complexes serve as catalytic initiators for cyclic polymer synthesis from alkynes. Specifically, they can initiate polymerization of alkynes to give cyclic polymers. The compounds have a carbon composition and include a site for a transition metal. Critical to their design is the presence of a unique supporting ligand containing a tethered M=C double bond that ensures the polymer chain ends remain attached to the metal ion. These initiators permit the synthesis of polymers with unique topologies such as cyclic dendronized polymers, cyclic brush polymers, and stereoregular cyclic polymers. Cyclic polymers are now finding potential application in drug delivery, low friction materials, viscosity modifiers, optical devices, anti-fouling surface modifiers, plasticizers, and melt flow modifiers.
