Commercially available poly(propylene glycol) (PPG) and poly(tetrahydrofuran diglycidyl ether) (PTG) alpha,omega-end-capped with epoxide functions have been chemically modified into alpha,omega-bis(cyclodithiocarbonate) (DTC) telechelic analogues. The neat stoichiometric reaction of PPG/PTG-Epoxide(2) with CS2 and LiBr enabled to prepare up to 300 g of the corresponding PPG/PTG-DTC2 functional polyethers. The subsequent one-pot, one-step aminolysis of the cyclodithiocarbonate end-groups of the polyethers using di- or polyamines, namely triethylene glycol diamine (Jeffamine EDR-148) and/or polyethylenimine (Lupasol), smoothly afforded the poly(mercaptothiourethane)/polyethers, as non-isocyanate polythiourethanes (NIPTUs) featuring pendant primary thiol groups. Ultimate cross-linking of the NIPTUs upon oxidation with MnO2 or through the Michael reaction of the pendant thiol functions with di- or triacrylates, afforded cured NIPTU materials. Detailed macromolecular and thermomechanical characterizations of the (cross-linked) polymer materials, including NMR, FTIR, and Raman spectroscopies, MALDI-ToF mass spectrometry, DSC analyses, and tensile and rheology tests, are reported.