Quantitative liquid C-13-n.m.r. has been extensively employed for the study of swollen gels. In the bulk tridimensional polyadditions of pure triricinoleate of glycerol (R(3)G) and castor oil (GO) with 4,4’-methylenediphenylisocyanate, 2,6-tolylene diisocyanate and 1,6-hexamethylene diisocyanate, the conversions of alcohol and of isocyanate groups were found to be limited by the crosslink density of the networks. The conversion limits were found independent of the natures of the diisocyanates incorporated. Critical times at the sol-gel transitions were localized by dynamic mechanical experiments. The conversion limits of OH groups determined in dense gels are only slightly larger than those found at critical times. Thanks to the conversion limits of dense gels and the known values of the R(3)Gs and COs weight-average functionalities of OH groups [<(F)over bar (W)>(OH)], a reliable graphical method has been established for the determination of <(F)over bar (W)>(OH) usable for other reactive prepolymers.