However, its Mn is 21.6 kg mol -1 , which is too high for a plasticizer . A transesterification reaction strategy with a short diol was thus considered to obtain controlled low Mn oligomers. As PHO is not soluble in BDO, a sustainable reactive solvent, diglyme was therefore used as a co-solvent with high-boiling point, for a reaction at 160 °C. The reaction is shown in Figure . The progress of the reaction is monitored by 1 H NMR until to obtain a Mn close to 800 g mol -1 . After 48 h of reaction, a plateau is reached, and the Mn no longer varies. The Mn of the starting PHO and the final PHO-diol are measured by 1 H NMR and SEC and reported in Table . Mn value is thus reduced by 18 during the reaction. This Mn can be reached in 1.5 hours by increasing the amount of DBTL to 50 eq/OH.