Characterization of hyperbranched polyol polyesters based on 2,2-bis (methylol propionic acid) and pentaerythritol



Hyperbranched polyesters (HBPs) of fourth and fifth generation were synthesized by procedures involving one step (HBP4, HBP5), step by step (HBP4P, HBP5P), and combination of both of them (HBP1-4, HBP1-5) using 2,2-bis(methylol)propionic acid (DMPA), pentaerythritol (PE), and acid catalysis. The characterization of the polyesters was done by nuclear magnetic resonance (NMR), rheology on solution, Fourier transform infrared spectroscopy (FTIR), and acid and hydroxyl values. The degree of branching of polyesters (DB) and the average molecular mass and polymerization degree NMR were calculated by Frey and Fréchet methods and (DP)NMR, respectively, being higher for HBP4P sample. The molecular structure of polyesters depends mainly on of the synthesis method. The hydroxyl values were larger than 430 mg/g KOH for all HBPs, and the conversion was controlled between 90 and 93% to avoid excessive cyclization reactions. The steady shear viscosities at different temperatures and at 41.77 s−1 shear rate were measured for all HBPs solutions in dimethyl formamide (DMF) showing a shear thickening behavior. The flow activation energies (Ea) were calculated by Arrhenius equation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009