The first RAFT mediated polymerization of methyl methacrylate initiated by diradicals derived from Bergman cyclization was performed employing 3,4-benzocyclodec-3-ene-1,5-diyne (BCDY) as diradical source and cyanoisopropyldithiobenzoate (CPDB) as RAFT agent. The polymerization was conducted in bulk at 80 degrees C for 3 h. The concentration of the enediyne was kept constant at 3.0 x 10(-2) mol . L-1 and the RAFT agent concentration was varied between 0.0 mol . L-1 and 2.4 x 10(-1) mol . L-1. A detailed ESI-MS analysis reveals the absence of intramolecular termination reactions (ring formation) in the RAFT mediated system, which usually makes diradicalic initiation unfavorable. The presence of polymeric chains propagating at both ends could be confirmed. The conversion of the RAFT mediated polymerization was up to more than two times higher than the RAFT free polymerization at identical conditions. Thus, polymers with narrow polydispersities (1.1 <= PDI <= 1.5) even at very high molecular weights (near 400 000 Da) were obtained within modest reaction times.