This paper deals with the theoretical aspect of the reaction between sec-butyllithium and equivalent quantities of m-diisopropenylbenzene. The expression of various molecular parameters of the resulting adducts, such as the molecular weight distribution function, the number- and the weight-average molecular weights, the functionality distribution and the average functionality, are given. By the aid of these expressions, we can gain insight into the reaction process. When the reaction is close to completion, precipitation is usually observed because x = 1 is the critical condition of the gelation for this reaction system, where x is the conversion of double bonds. In the meantime, the average functionality approaches 2 even though 37% of the sec-butyllithium initially added to the system remains unreacted and joins in the monofunctional adduct at the end of the reaction. In general, the theoretical results are in agreement with the experimental data reported by Cameron and Buchan (Polymer, 1979, 20, 1129).