Four cycloaromatization substrates each produce diradicals that lead to the initiation of polymerization of vinyl monomers. All the initiators produce significant amounts of polymer, especially with methacrylate monomers. Intramolecular termination of short diradical chains produces oligomeric byproducts and limits the amount of high polymer that is formed. The polymer yield can be increased through the addition of a chain transfer agent by presumably converting unproductive diradicals into pairs of monoradicals. The enediynes that contain terminal acetylenes are less effective initiators because they retard radical polymerization. Bergman cyclization substrates are better initiators than Myers cyclization substrates.