A number of unsaturated silanes which are functionally capable of polymerizing by the cyclopolymerization mechanism have been synthesized and their polymerization studied. Allyl-substituted silanes studied include diallylmethylphenylsilane, diallylcyclotetramethylenesilane, and diallylcyclopentamethylenesilane. The latter two compounds have been characterized, and their physical properties are reported since they are new structures. Methallyl-substituted silanes studied include dimethallyldimethylsilane, dimethallyldiphenylsilane, dimethallylmethylphenylsilane, and dimethallylcyclopentamethylenesilane. The latter compound has been characterized, and its physical properties are reported since it is a new structure. Also, allylvinyldimethylsilane was prepared, characterized, and studied, since this compound is functionally capable of producing a five-membered ring in the repeating unit of the polymer. All of the diallylsilanes yielded polymers of low molecular weight by use of coordination catalysts of the Ziegler type. The dimethallylsilanes failed to yield polymer via coordination initiators but yielded low polymers by a free radical machanism. Allylvinyldimethylsilane yielded a low, noncyclic polymer via coordination initiation in which only the allyl double bond participated. By the free radical mechanism, polymers of similar structure were obtained.