A new technique for the preparation of poly(diethylsiloxane) (PDES) is described. The monomer hexaethylcyclotrisiloxane is polymerized with NaOH as a catalyst in the presence of the promoter 12-crown-4 (1,4,7,10 tetraoxacyclododecane). The effects of NaOH concentration, 12-crown-4 concentration, and polymerization time on the molecular weight distribution are reported. A mechanism for the polymerization is proposed based on current knowledge of anionic ring-opening polymerization of cyclic siloxanes. The advantages and disadvantages of this synthesis relative to previously published PDES syntheses are discussed.