Tannins from Pinus pinaster bark were modified with propylene oxide (PO) in aqueous alkali at room temperature (similar to 22 degrees C) for the first time. The hydroxypropylation to four different degrees of substitution (DS) produced derivatives (HPT) with monosubstituted phenolic functionalities in yields in excess of 80%. The isolated HPTs were characterized by FT-IR, UV-vis, H-1 NMR and bidimensional spectroscopies (HMBC, HSQC and COSY). The integration of the aromatic proton signals in the H-1 NMR spectra of acetylated HPT allowed for an easy quantitative determination of DS. HPTs possess properties that are expected to enhance their role in new oligomeric building-blocks for the synthesis of engineered plastics and tannin-based bio-foams.