ADMET polymerization has been used to synthesize telechelic elastomers having silacyclobutane end groups. Subsequent thermal treatment leads to a controllable ring-opening reaction to form thermally stable thermoset materials. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.] Additional Supporting Information may be found in the online version of this article. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.