In 1956 Roberts and co-workers synthesized 3-methylenecyclobutene and prepared three polymers by cationic, anionic and free radical methods. Based on IR spectra or the polymers, they concluded that the bulk cationic polymerization of 3-methylenecyclobutene gave predominantly the 1,5-structure, while anionic polymerization by KNH2 in liquid ammonia produced primarily 1,2-addition repeating units. In the free radical homopolymerization of this cyclic diene, they proposed that all types of 1,2-addition, 3,5-addition and 1,5-addition mechanisms were operative. Since this initial brief study, no further investigation of the polymerization of 3-methylenecyclobutene has been reported to date in the literature. It is, therefore, the objective of this project to examine in greater detail the polymer structures obtained by different types of initiators and thus to help elucidate the polymerization mechanisms involved, through the use of high resolution NMR and IR spectroscopy. In the course of this study, it was observed that poly-3-methylenecyclobutene prepared cationically was susceptible to very rapid autoxidation and crosslinking reactions, which complicated the polymer characterization.