Preliminary dissolution tests for the products were performed (Table ). The primary observation of these tests was that S42 is essentially insoluble in water and investigated alcohols. This could be considered as a first clue about decreased hydrogen bonding ability of the modified polymer due to increased number of thioamide moieties. In size exclusion chromatography, we observe a slight but noticeable shift to lower molar mass after thionation, except for S3 (Figure ). A shift to lower molar mass has been observed for S42 sample. We attribute this to a partial collapse of polymer coil due to a reduced solvent compatibility of the thionate repeat units. Alternatively, this could potentially be interpreted as a polymer degradation, but we consider this shift unlikely to originate from degradation reactions, as the molar mass distribution function shifts smoothly. For the determination of the degree of thionation, 1 H-NMR spectroscopy was used. The 1 H NMR spectra of S0 are characterized by three main signal groups, the side chain methyl group at δ = 0.95-1.05 ppm, the side chain methylene group at δ = 2.2-2.4 ppm and the backbone protons give rise to a signal around δ = 3.3-3.45 ppm (Figure , signals 1, 2 and 3). The thionation shifts signal 1 to δ = 1.22 ppm (Figure , signal 1'). Signals 1 and 1' are ideally suited for quantification, as they remain isolated, and baseline separated at all thionation degrees. Accordingly, the degree of thionation was calculated as the ratio of the integrals I1'/(I1 + I1'). Also, the signals attributed to the backbone and side chain methylene shift to higher ppm values with increasing thionation, due to shielding of the sulfur atoms with bigger electron clouds (Figure , signals 2',3'). Importantly, these new signals are much broader and more split up. Especially signal 3' becomes very broad from δ = 3.6 ppm up to δ = 4.3 ppm. We assume that the extreme broadening of signal 2' and in particular 3' are connected to the larger energy barrier between cis-and trans-form of the thioamide vs. amide. The absence of the sharp signals 2' and 3' and suggests that the thionation is occurring randomly along the polymer chain instead of in a block-like fashion. Sulfur to nitrogen ratios from elemental analysis corroborated NMR analysis rather well (Table ). Thermogravimetric analyses were performed under synthetic air atmosphere. Decomposition onset temperatures, and 20% decomposition temperatures decrease with increasing degree of thionated polymers compared to unmodified PEtOx sample (Figure ) with S16, S20 and S42