The first step in the synthesis of oligoPBAT-diol was a solvent-and catalyst-free transesterification of PBAT by BDO (Figure ), according to a protocol derived from previous studies [11] 39,4052 , allowing a Mn decrease and an increase the reactive OH chain ends density (Figure ). OH and carboxylic acid (COOH) end-groups contents of oligoPBAT-diol were estimated by quantitative 1 H and 31 P NMR. The results were summarized in Table in SI. The phosphitylation reaction performed prior to 31 P NMR analysis could be impeded by the steric hindrance induced by TMDP, and then can lead to an underestimation of the chain ends content . In this way, for the determination of the quantities of reagents in the following synthesis steps, the contents determined from quantitative 1 H NMR were used, rather than the results obtained from 31 P NMR. The fraction of residual BDO OH groups was determined by P NMR (Figure in SI). This result was used to modify the OH chain ends content obtained by quantitative 1 H NMR (Table in SI), since the peaks of residual BDO and oligoPBAT-diol OH chain ends cannot be separated by 1 H NMR. From these results, the oligoPBAT-diol used for oligoPBAT-dithiol synthesis had an OH content of 1.6 mmol g -1 and a fraction of residual BDO OH groups equal to 9 mol%. Due to the rather close reactivities of thiol and OH groups, the thiol groups of thioglycolic acid must be protected before starting the reaction with oligoPBAT-diol (Figure ). 2,4-Dinitrofluorobenzene, also known as Sangers reagent, was used to this task. Its fluorine atom underwent a base-catalyzed aromatic nucleophilic substitution by the thiol of thioglycolic acid . DNTPAA was recovered in the form of yellow crystals, with a yield of 73 mol%. After vacuum-drying, this product was analyzed by 1 H and C APT NMR to confirm the chemical structure (Figure ). We can show that the CH2-SH doublet of thioglycolic acid at 3.3 ppm (Figure in SI) was replaced by a singlet at 4.2 ppm, because of the formation of a new C-S bond. In 13 C NMR, the corresponding carbon atom was also strongly shifted from 26.3 for thioglycolic acid (Figure in SI) to 34.5 ppm for DNTPAA. Some residual peaks of TEA with very low intensities were also recorded on the 1 H NMR spectrum of DNTPAA 55 . P NMR, which allows the identification and quantification of labile protons, such as OH, COOH and SH, after phosphitylation, with high signal resolution and peaks separation , was performed on thioglycolic acid and DNTPAA, as reported in Figure in SI. OligoPBAT-diol was then reacted with DNTPAA to esterify the OH chain ends through a Mitsunobu reaction (Figure ), with a mechanism given in the literature . Briefly, DIAD and TPP react in a first step to form a betaine, which deprotonates the COOH group of thioglycolic acid, forming a salt. The DIAD-TPP cation then reacts with the OH chain ends to form oxyphosphonium intermediates, which finally undergo an SN2 reaction to yield the ester products and triphenylphosphine oxide.