Hyperbranched polyglycerols (DPn = 23-83; M-w/M-n = 1.2-1.5) as well as their propoxylated derivatives were esterified to different extents (23%-100%) with various carboxylic acids (C2 to C18, benzoic, biphenylcarboxylic, and benzoic acid). Composition and molecular weight of the hyperbranched polyether scaffolds were varied with absolute molecular weights (NMR) ranging from M-n = 1800 to 12 400 g/mol. Complete or partial esterification did not affect the narrow polydispersities of the hyperbranched polymers, which were in the range 1.2-1.5 for the esterified polyglycerol samples and 1.2-1.9 for the esterified propoxylated polyether polyols. The parameter a (fractional molecular weight increase) was introduced, which permitted to demonstrate that SEC separates the branched polymers according to hydrodynamic volume. Because of the narrow polydispersity, the samples could be studied systematically by DSC, showing that the flexibility, i.e., T-g, of the hyperbranched polymers is controlled mainly by two factors: (i) the extent of hydrogen bonding and (ii) the formation of order (mesophases, crystallization), which raises the T-g. T-g＇s of the esterified polyether polyols were in the range -58 to -22 degrees C, showing the scope and limitations of tailoring the thermal properties of hyperbranched polymers by means of derivatization.