OIL MODIFIED BY TRANSESTERIFICATION WITH PENTAERYTHRITOL.Castor oil was reacted by transesterification with various percentages in mass of pentaerythritol to obtain different esters of pentaerythritol.Alternatively, glycerol was also used instead of pentaerythritol for the same reaction in order to establish comparative reference products.The products of the reactions were characterized by matrix-assisted laser desorption/ ionization time-of-flight mass spectroscopy in order to detect and quantify (in terms of the molecular mass and structural information) the components of the products obtained.Analysis for hydroxyl value, acid value, viscosity and specific gravity were used to complete the characterization of the polyols obtained and also of the original castor oil.The polymer characterization was accomplished by tensile stress-strain tests, Shore A hardness, thermogravimetric analysis and chemical resistance to solvents.