The n-BuLi-initiated polymerization of(CH2=CHMe2Si)(2)NR (R = Me, 1; R = SiMe3, 2) gave highly regular polymers 3 and 4 which consisted entirely of linked cyclic units with no detectable crosslinks or linear segments. The substituent R profoundly affected the ring size found in the resulting cyclopolymer: monomer 2 gave only five-membered rings in the polymer backbone, while 1 formed both five- and six-membered rings. The stereochemistry of polymerization of 2 was found to be solvent-dependent: the ratio of cis to trans five-membered rings in 4 increased when the reaction was conducted in the presence of coordinating cosolvents (e.g., Et3N). Polymers 3 and 4 could be cleanly ring opened with HF(aq) to give poly(vinyldimethylfluorosilanes) 7 and 8. The synthetic utility of polymer 8 was demonstrated by its reaction with a variety of nucleophilic reagents to give highly regular, highly functionalized polymers of the type (CH2CHSi(CH3)(2)R＇)(n).