The free-radical cyclopolymerization of[Ph(2)P(CH2CH=CH2)(2)]Br-+(-), initiated by 4,4’-azobis(4-cyanovaleric acid) (azo-CNV) and by Co-60 gamma-radiation, and of [Ph(2)P(CH2CH=CH2)(2)](PF6-)-P-+, initiated by azo-CNV, has been investigated. P-31 NMR studies indicated that the major structural components of the polymers are five- and six-membered cyclic phosphonium units but that some linear components can be present as well. Basic aqueous hydrolysis converted these phosphonium salt cyclopolymers to the respective polymeric phosphine oxides. GPC molecular weight studies of the latter were carried out. The phosphonium salt cyclopolymers were converted to polymeric cyclic phosphorus ylides by deprotonation with NaCH2S(O)CH3 in DMSO. Reactions of the polymeric ylides with benzaldehyde and allyl bromide were carried out. The GPC molecular weight determinations of the product of the reaction of the polymeric ylide with benzaldehyde provided indirect evidence for the presence or absence of linear units in the polymeric phosphonium salt.