Abstract
AbstractWe investigated the effects of annealing on the rearrangement of the H‐bond network microstructure and its influence on the thermal and rheological properties of the second pseudo‐generation hyperbranched (HB) polyester based on 2,2‐bis(methylol)propionic acid (Boltorn H20) in comparison to the fourth pseudo‐generation HB polyester (Boltorn H40). During annealing the hydroxyl groups of HB polyesters form H‐bonds with other hydroxyl or carbonyl groups. The formation of OH…OH H‐bonds is favored at shorter annealing times, higher annealing temperatures, and for low pseudo‐generation HB polyester, which has a low average molar mass, degree of branching, and core functionality. At temperatures up to 80 °C, Boltorn H20 indicates faster and more extensive H‐bond formation as compared to Boltorn H40. This is reflected in its larger cleavage enthalpies and higher elastic contribution to the viscoelastic response. At 90 °C and above, the process of H‐bond formation is delayed. Therefore, Boltorn H20 exhibits only viscous behavior in rheological measurements, and in DSC curves it shows strong exothermic transitions while heating the sample.magnified image
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