Hydroformylation of methyl soyate produces a mixture of fatty acid methyl esters with zero, one, two, and three hydroxyl groups, the major component being with two hydoxyls (around 50%). Polymerization of methyl esters of hydroxy fatty acids gives a hyperbranched product with a different content of hydroxyl groups depending on the degree of conversion. Molecular weights can be controlled by controlling the degree of conversion but also using monofunctional components. A range of hyperbranched polyols with acceptable viscosities and functionalities, suitable for flexible applications, was obtained by stopping the reaction at varying degrees of conversion. Monte-Carlo simulation of the polymerization of hydroxylated methyl soyate gave molecular weights and polydispersity which were compared with experimental values. Although hydroxylated methyl soyate contains considerable amounts of mono- and difunctional fatty acids, the system produces a physical gel at the highest conversions. This is due to very high molecular weights and was confirmed by experiments and the simulation. The simulation unexpectedly gave lower molecular weights but wider distribution than the experiments. This discrepancy was explained by the combination of experimental difficulties and possible side reactions leading to higher molecular weights. Functionality of polyols determined from gel points at critical NCO/OH ratios was reasonably close to predictions. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012