AbstractExperiments on networks crosslinked by peroxides show that the amount of extracted molecules as well as the time needed for a dissolution of a network during random degradation and the molecular mass“Relative molecular mass” (systematic IUPAC name) is shortened to “molecular mass” throughout this paper.of high molecular mass degradation products may be used to determine previously inaccessible structural details, such as molecular mass of the network chains, weight fraction of chains with one free end, functionality of the crosslinks, and inhomogeneity of crosslinking, i.e. the amount, the diameter, and the concentration of crosslinking units of anomalously and strongly crosslinked regions. In crosslinking of polydienes, chain splitting is negligible, but the functionalities of the crosslinks are abnormally high for low peroxide concentrations, because the peroxide radicals may connect more than two chains by polymerization. A relatively high spatial inhomogeneity of the concentration of crosslinking units occurs with polybutadienes, presumably because the radicals of this polymer have especially long life‐times so that they can polymerize sequences of polyfunctional crosslinks via kinetic chains with transfer reactions. In crosslinking of polyisoprene the apparent efficiency of this peroxide is about 1,0 if one takes into account not only the number of crosslinks, but also that of loops, and if one neglects transfer. The efficiency of this peroxide is ≫ 1 in the crosslinking of polybutadiene, because of pronounced transfe