The assessment of the chemical structures was performed with 1 H NMR and the spectra of the synthesized copolymers are presented in Figure . The most intense signal appeared at δ1H = 2.6 ppm which is responsible for methylene protons of dimethyl succinate (DMS). The outer and inner methylene protons of PBS appeared at signals δ1H = 4.12 ppm and δ1H = 1.71 ppm, respectively. The appeared signals at around δ1H = 4.06-4.08 ppm were assigned to the formation of ester bonds between DLS-OH and DMS. The major change in the spectra appeared after addition of PEG as manifested by the signal at δ1H = 3.68 ppm (Figure ; i). This signal represents the methylene units of the PEG which are attached to the ether group of the copolymers. Another obvious change between copolymers differing in segmental ratio is the higher intensity of the signal δ1H= 1.27 ppm for the copolymers containing 40 wt% of DLS soft segments. This signal is assigned to the methylene units of the DLS within the aliphatic chain and confirms the presence of higher soft segment content. Since NMR spectroscopy is known as a viable analytical technique for determination of the average molecular weight (Mn) of the polymers, therefore the molecular weight, the degree of polycondensation of the hard segments (DPh) and molar ratio between the PBS-DLS-PEG were calculated according to the previously reported method Table shows the summary of the theoretical and calculated molar/weight mass results and composition based on 1 H NMR and the molecular weight from GPC analysis. The comparison of the weight percentage results between the theoretical values and those calculated from 1 H NMR analysis, indicate that a higher amount of PEG soft segments has been incorporated into the copolymers. When utilizing the heterogeneous C-94 catalyst , the calculated ratio of hard segment to soft segment in the synthesized polymers deviated significantly from the theoretical values. For example, in the case of PBS-DLS 70-30 (hard segment to soft segment ratio), the experimental ratio obtained was 64-36. Similarly, for PBS-DLS-PEG with a theoretical ratio of 70-25-05, the experimental ratio obtained was 80-08-10 . However, with the use of the magnesium-titanium butoxide catalyst, the calculated ratios of the hard segment to soft segment in the synthesized polymers were found to be in close agreement with the theoretical values. For example, in the case of PBS-DLS with a theoretical ratio of 70-30, the experimental ratio obtained was 71-29. Similarly, for PBS-DLS-PEG with a theoretical ratio of 70-25-05, the experimental ratio obtained was 69-24-07. These results suggest that the magnesiumtitanium butoxide offers better control over the polymer composition and enables the synthesis of polymers with ratios closer to the desired theoretical values. The values of the molecular weight, calculated from the 1 H NMR are consistent with the results obtained from the GPC, indicating slightly lower molecular weight in copolymers with lower hard segments (60 wt%) compared to those with 70 wt%, and being consistent with higher molar percentage of hard segments incorporated: 89 mol% in PBS-DLS 70-30 and 84 mol% in PBS-DLS 60-40. After incorporation of PEG into the polymeric chain, however, the molecular weight decreased in both segmental ratios. Such results were also reported in other studies, where incorporation of higher molecular weight of PEG into the PBS, caused reduction of molecular weight. This was ascribed to much higher transesterification activation energy needed to reach higher Mn in case on PEG with high molecular weights. In our work, we were applying the same duration time for all steps and for all composition, regardless high Mn of PEG (6000 g/mol) (see Table in Supplementary information). The PBS-DLS-PEG copolymer structure was also assessed by ATR-FTIR spectroscopy. Figure shows absorbance bands characteristic for PEG appearing at 840 cm -1 , 1058 cm -1 , 1097 cm -1 , 1145 cm -1 which are assigned to C-O and C-C stretching of PEG. For the PBS-DLS copolymers, absorbance bands at 2920 cm -1 and 2855 cm -1 are assigned to -CH2-stretching vibration of the methylene groups of the DLS soft segments. Intensities of these bands are higher for copolymer PBS-DLS 60-40 wt% containing higher content of DLS soft segments. Absorbance bands at around 1710 cm -1 and 1150 cm -1 represent the C=O carbonyl vibrations and ester C-O-C bond stretching, respectively characteristic for polyesters. After incorporation of 5 wt% of PEG into the copolymers (PBS-DLS-PEG), small bands appeared at around 1070 cm -1 , which were identified as C-O stretching vibration of ether bonds, confirming the successful incorporation of PEG into the polymer structure.