AbstractSome unexpected results were observed in the phase transfer of catalyzed (PTC) (two phase, aqueous‐organic) polymerization of α,ω‐dibromoalkanes with sodium sulfide. Alkane dielectrophiles containing fewer than six methylene units give rise to large, and sometimes quantitative, amounts of cyclic thioethers. These cyclic sulfides are formed under “polymerization” conditions and can be minimized by using only the monomer as the organic phase. Alkane dielectrophiles containing more than six methylene units yield only polymer. When a comonomer system composed of a 1:1 mixture of 1,4‐dibromobutane (DBB) and 1,8‐dibromooctane (DBO) is employed, the resulting copolymer's molecular weight and polydispersity are vastly improved compared to the corresponding homopolymerizations. Microstructurally, this copolymer is formed by complete consumption of DBO and partial incorporation of DBB. The remaining DBB forms tetrahydrothiophene (THT). These two odd and seemingly conflicting results could not be explained by “normal” or “inverse” PTC extraction mechanisms. Support of this new mechanism is given in the PTC polymerization of DBO with sodium sulfide in the presence of a catalytic amount of THT. The resulting polymer is of very high molecular weight and narrow polydispersity; it also does not contain tetramethylene sequences. Using this new mechanism, all results suggest the participation of cyclic sulfides either facilitates cyclic formation or enhance polymer reactivity as controlled by the length of the