A first-generation Grubbs catalyst has been shown to not only catalyze the ring opening metathesis polymerization (ROMP) of cyclopropene derivatives but also differentiate E- and Z-double bonds in intermediates by different reaction patterns, leading to stereospecific synthesis of poly(methylene-E-vinylene). The intermediate with the Z-double bond formed during the course of ROMP of cyclopropene is sensed by the catalyst, chopped by the catalyst, and removed as the cyclohexadiene derivative, and in the meantime, a ruthenium-carbene species is regenerated for continuing polymerization. When a second-generation Grubbs catalyst is used, a cyclic polymer with all double bonds in the trans configuration is obtained as the sole polymeric product, in addition to the same cyclohexadiene derivative as described above. The degree of polymerization in the latter reaction is independent of the loading of the catalyst. The formation of cyclic polymer is not common and the mechanism thereof remains unclear. One possibility would be a change in conformation of the alkenyl substituents on azetidine rings that would result in alteration of the folding nature of the polymer, leading to a cyclic polymer via ring closure metathesis.