Hyperbranched poly(butylene oxide) polyols have been synthesized by multibranching anionic ring-opening copolymerization of 1,2-butylene oxide and glycidol. Systematic variation of the composition from 24 to 74% glycidol content resulted in a series of moderately distributed copolymers (D = 1.41-1.65, SEC), albeit with limited molecular weights in the solvent-free batch process in the range of 900-1300 g mol(-1) (apparent Mn determined by SEC with PEG standards). In situ monitoring of the copolymerization kinetics by 1H NMR showed a pronounced compositional drift with respect to the monomer feed, indicating a strongly tapered microstructure caused by the higher reactivity of glycidol. In the case of slow monomer addition considerably higher apparent molecular weights up to 8500 g mol(-1) were obtained (SEC). By alteration of the comonomer ratio, aqueous solubility of the hyperbranched copolymers could be tailored, resulting in well-defined cloud points between 20 and 84 degrees C. Glass transition temperatures between -60 and -29 degrees C were observed for the resulting polyether polyols. High degrees of branching (DB) between 0.45 and 0.77 were calculated from inverse gated (IG) 13C NMR. Online viscosimetry and analytical ultracentrifugation (AUC) were employed to study hydrodynamic properties and to establish a universal calibration curve for the determination of absolute molecular weights. This resulted in Mw values between 2100 and 35?000 g mol(-1) that were generally 2-3 times higher than the apparent values determined by SEC with linear PEG standards.