Oxyalkylation of gambier tannin-Synthesis and characterization of ensuing biobased polyols

For the first time, condensed tannin was fully oxypropylated with KOH as a catalyst, in a high pressure batch reactor. Tannins are the most abundant source of natural aromatic molecules without fragmentation steps. Different tannin derivatives based polyols with a final biobased content up to 42%, have been synthesized and characterized. To better understand the conditions and mechanisms of the synthesis, the influence of the tannin/propylene oxide ratio and the catalyst content was assessed through the evolution of OH content, homopolymer content, molecular weight distributions and the viscosities. Besides, the thermal properties have been evaluated to better understand the final molecular architectures. In all cases, the number of grafted chains was steady (11 chains per tannin molecule). The main difference between the polyols can be seen in the length of polypropylene oxide grafted chains (between 1.9 and 3.1 units) which can be controlled by modulating oxypropylation reaction parameters. (C) 2015 Elsevier B.V. All rights reserved.