AbstractThree samples of a commercial hydroxyl‐terminated polybutadiene, Arco R45M. were characterised with respect to number‐average and weight‐average molar mass, intrinsic viscosity, number‐average hydroxyl functionality and effective functionality for gelation. Two of the samples were fractionated on the basis of solubility in toluene/methanol mixtures, and the fractions were characterised with respect to number‐average molar mass, intrinsic viscosity and number‐average hydroxyl functionality. For both sets of fractions, the average functionality was practically independent of average molar mass. It is concluded that the functionality distribution is almost identical at all points in the molar mass range of Arco R45M.