Known ways to tune the cloud point of PEtOx solutions are controlling molecular weight, polymer architecture, and modifying solvent quality, e.g. by adding Hofmeister salts into the system. The first study about the solution behavior of high molecular weight PEtOx samples reports a maximum Tcp of 70 °C. Later studies showed PEtOx-water systems have a Flory-Huggins type I behavior with continuous demixing upon heating. By decreasing the molecular weight of the PEtOx, Tcp increases. The lowest limit of molecular weight to observe the LCST behavior for linear PEtOx was found to be approximately 10 kDa. However, shorter fragments in different copolymer architectures such as block copolymers and brushes that yield higher local PEtOx concentration, have also been reported to yield thermoresponsiveness. Accordingly, starshaped architectures show lower Tcp in solution compared to linear polymers with same molecular weight. Another way to tune the solution behavior of POx is synthesizing random or gradient copolymers with repeating units of varying hydrophobicity, allowing to adjust the Tcp essentially over the entire range of liquid water. Chen et al. first showed that the LCST of PEtOx is dependent on hydrogen bonding between the amide carbonyl water molecules by comparing Tcp 's of polymer solutions in water and deuterium oxide. Thioamides are variants of amides with sulfur replacing the carbonyl oxygen atom, giving them unique physicochemical properties. This substitution results in a lower oxidation potential and a greater affinity for metals compared to regular amides. Thioamides have higher rotational barrier around the carbon nitrogen bonds compared to amides which makes them more rigid. They are rather rare in nature as thiopeptides, mostly of bacterial origin, with antimicrobial and metal chelating properties. Thioamide insertion was also studied in protein and peptide engineering as photo-switches, fluorescence quenchers or tuning their pharmacokinetic properties. Apart from protein engineering, thioamides have been used commonly as synthetic intermediates in organic chemistry. Thionated cyclic oligoamides or polyamides has also been investigated to increase their metal binding capacities for water purification purposes. For the synthesis of polythioamides, multicomponent reactions involving elemental sulfur are mostly being used for the polymers which can be synthesized via polycondensation reactions. However, very early attempts for accessing the thio-analogues of water-soluble polymers can be found in the literature with limited characterization, in particular for poly(N-vinylpyrrolidone) and poly(Nvinylcaprolactam). Another interesting feature of thioamides is that their sulfur lone pairs are weaker hydrogen bond acceptors relative to oxygen lone pairs in amides. Therefore, we hypothesized that thionating a polyamide with LCST type behavior should affect its solution properties. If hydrogen bonding is the driving force of phase separation in aqueous PEtOx solutions upon heating, inserting weaker hydrogen bond acceptor moieties should result in decreased solubility. In this study, we are reporting thionation of PEtOx with Lawesson's reagent (LR) for the first time. We obtained random poly(2-ethyl-2-oxazoline-co-N-propanethioacetyl ethylene imine) copolymers with different and controllable thionation degrees. The solution behaviors of synthesized polymers in water were examined using turbidity measurements.