In this contribution, high-throughput screening experiments are reported to study the polymerization of different aromatic polyurethane (PU) prepolymers. The prepared prepolymers were synthesized from toluene diisocyanate (T80) with different molar mass polyether diols and polyether triols, respectively. The reactions were performed in solution using a Chemspeed Accelerator (TM) SLT106 automated parallel synthesizer as well as in bulk to evaluate the high-throughput approach for this kind of prepolymers. More than 100 samples were prepared and characterized by GPC within 1 week labor time to investigate the reaction kinetics and to compare the resulting trends obtained by high-throughput experimentation (HTE) or by conventional, bulk prepolymerization. The synthesis of the prepared prepolymers with a linear (T80-Diol) or a branched (T80-Triol) structure followed a second-order kinetic in solution but showed deviation from this phenomenon in bulk under the selected reaction conditions, although the same trends are observed in both cases. The calculation of the rate constants allowed comparing the reactivity of different prepolymer systems, which could have a significant influence on the industrial application and processing of these materials. As a result, the HTE approach was found to represent a powerful tool for the kinetic studies of PU prepolymers. Moreover, in spite of the complexity of the curing process, the results obtained by high-throughput solution polymerization can be applied for evaluating the bulk polymerization. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 570-580, 2010