Small concentrations up to 10(-6) mol/cm(3) of C-60 fullerenes influence on both the molecular and topological structures changing at synthesis and the related mechanical properties of linear (pseudonetworked) and crosslinked polyester urethane ureas (PEUU). A crosslinked PEUU was synthesized on the base of poly(oxypropylene) macrodiisocyanate (POPMDIC) and 3,3-dichloro-4,4'-diaminodiphenylmethane (MOCA) with virtually an equimolar ratio of amine and isocyanate groups, but the linear polymer was obtained with twofold molar excess of amine groups. Fullerenes change the network density, the share of the physical branching junctions and molecular weight distribution (MWD) of the chain segments between the networking junctions. Additionally, molecular weight and the polydispersity index increase with C-60 concentration in the reaction blend. This evidences to a branching role of C-60 during their interaction with terminating amine groups. An influence of MWD of the chain segments between the networking junctions on tensile strength of the crosslinked and linear polymers was assumed. (c) 2007 Wiley Periodicals, Inc.