Theoretical and experimental studies in the literature on the coupling between functionalized polymer chains at immiscible polymer-polymer interfaces have always involved second-order kinetics. In addition, the time dependence of the degree of copolymer formation has been predicted to vary depending on the reaction stage. However, on the basis of careful reanalysis of the actual reaction orders in published work and our own experiments in the polyamide (aPA)/polysulfone (PSU) system, it is demonstrated that pseudo-first-order kinetics in the parameter (Sigma* - C) are universally obtained over the whole time scale. The quantities Sigma and Sigma* are respectively the areal density of copolymers formed at time t and at infinite time at the interface. It indicates the time dependence of Sigma similar to -exp(-t) at all stages. On the basis of these results, a new reaction model is proposed, in which coupling is viewed as involving the formation of a two-dimensional monolayer on the interface surface by copolymers formed in situ. The coupling process giving rise to the pseudo-first-order kinetics is considered to be reaction-controlled.