Polycondensation of H3PO4 with diglycerol (DGL) involves biobased, commercial products and leads, via hydrolyzable gels, to highly branched reactive macromolecules. These reactive macromolecules have been applied as multiacidic catalysts with hydroxyl groups in polymerization of l-lactide, consuming entirely the starting highly branched macromolecules. Polycondensation was performed in bulk, at 110-120 degrees C with efficient elimination of water under vacuum. The process with DGL differs substantially from the previously studied polycondensation with ethylene glycol and glycerol. Formation of pyrophosphoric acid (PY) constitutes the rate determining step: the rate of PY formation is the same in the absence and presence of DGL. Kinetic studies explained why the rate of monoesters (M) accumulation may be the same as the rate of accumulation of di- (D), and triesters (T). This is because the rate of M formation is relatively low when compared with rates of further reactions of M, leading to D and T. (c) 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3303-3317