The precise functionalization of polyethylenes, often accomplished through acyclic diene metathesis polymerization (ADMET), is a significant area of research that has improved polyethylene properties and performance. Here, the synthesis of precisely functionalized polyethylenes was accomplished using the thiol–ene step-growth (TES) polymerization. The simplicity and versatility of this technique allowed for the synthesis of a variety of polymers and enabled the study of carbon spacer length between and repeat unit symmetry about the resulting backbone thioether moiety. In addition, the backbone thioethers of some samples were functionalized postpolymerization with methyl triflate to produce polyethylenes containing sulfonium cations. All polymers were then characterized for their thermal stability, crystallinity, and morphology using differential scanning calorimetry (DSC) and X-ray scattering. While the carbon spacer length and repeat unit symmetry had no effect on polymer thermal stability, the incorporation of cationic sulfonium groups reduced the degradation temperature. Most polymers were polymorphic with respect to crystal structure, and increasing the carbon spacer length led to an increase in polymer melting temperature and percent crystallinity. Furthermore, the average carbon spacer length had a larger effect on polymer percent crystallinity and crystal structure than repeat unit symmetry, but the symmetry had a significant impact on polymer crystal melting temperature, as symmetric polymers had higher melting temperatures. Overall, TES polymerization was utilized to fabricate precisely functionalized polyethylenes, where the repeat unit symmetry improved polymer crystal perfection.