The heterochain crosslinking theory is applied to postgel behavior in the free-radical crosslinking copolymerization of vinyl and divinyl monomers. In this context, the crosslinked polymer formation can be viewed as a system in which the primary chains formed at different times are combined in accordance with the statistical chain-connection rule governed by the chemical reaction kinetics. Because the primary chains are formed consecutively, the number of chain types N must be extrapolated to infinity, N --> infinity. Practically, such extrapolation can be conducted with the calculated values for only three different N values. The analytical expressions for the weight; fraction and average molecular weights of the sol fraction are derived for the general primary chain length distribution function in free-radical polymerization. Illustrative calculations show that the obtained results agree with those from the Monte Carlo method, and that the postgel properties in free-radical crosslinking copolymerization systems could be significantly different from those in randomly crosslinked systems.