Chain Transfer in the Ring-Opening Metathesis Polymerization of Cyclooctadiene Using Discrete Metal Alkylidenes

The ring-opening metathesis polymerization of cyclooctadiene (COD) in the presence of a difunctional chain transfer agent (CTA) was investigated. The effect of the CTA structure and choice of metathesis catalyst on the overall efficiency of the polymerization reaction is discussed. A separation of the oxygen functionality from the olefin in the CTA by two methylene units significantly enhances the stability of the discrete, tungsten-based metathesis catalyst used for these polymerizations. Furthermore, a more robust well-defined metathesis catalyst based on molybdenum was more effective than the tungsten-based catalyst. The preparation oflow-molecular-weight hydroxytelechelic polybutadienes with one type of regiochemistry, number-average functionalities that approach 2.0, and in high yield was accomplished.