A wide variety of diunsaturated phosphonium salts have been synthesized in order to determine whether or not such structures undergo cyclopolymerization. As intermediates for these monomers, a number of previously unreported unsaturated phosphines have been prepared and characterized. Polymerization studies using a wide variety of free radical initiating conditions led to polymers in those cases which were predicted to undergo cyclopolymerization leading to five-, six-, or seven-membered rings with one exception. The properties of the polymers are consistent with the cyclopolymerization mechanism. The conversion of poly(diallyldiphenylphosphonium bromide) to polfidiallyldiphenylphosphine oxide) offers additional evidence for cyclopolymerization. Di-3-butenyldiphenylphosphonium bromide, a monomer functionally capable of forming a polymer containing an eight-membered ring, did not polymerize. Divinylphenylphosphine was found to undergo copolymerization with acrylonitrile in accordance with the cyclo-copolymerization mechanism.