A new experimental approach for preparing bio based water soluble polyesters (PEs) via titanium(IV) n butox ide catalyzed bulk polycondensation is presented In the described method polymers were obtained from isosorbide maim anhydride and poly(ethylene glycol) (PEG) The chemical structure of the synthesized PEs was confirmed using 2D NMR spectroscopy and by titration methods Careful analysis of 2D NMR spectra viz correlation spectra (COSY) heteronu clear single quantum correlation spectra (HSQC) and heteronu clear multiple bond correlation spectra (HMBC) allowed to accomplish the complete proton assignment of isosorbide PEG and unsaturated acid residues in the PEs Moreover by using NMR spectroscopy the transformation of maleic anhy dride into fumaric acid ester and the absence of maleic acid ester units in the final polymer were proven However during polycondensation part of the unsaturated bonds has reacted in a Michael addition with isosorbide or PEG Gel permeation chromatography measurements revealed that the unsaturated PEs have M-n values in the range 3000-5000 g/mol These PEs with a low content of carboxylic acid end groups exhibited sufficient thermal resistance for practical applications for example as free radical curable coatings (C) 2010 Wiley Periodi cals Inc J Polym Sci Part A Polym Chem 48 5907-5915 2010