Formation and transformation of additive sorption centers in isotactic polypropylene was studied. According to a two-component model of a polymeric substance, these centers are formed around the elements or units of disorder (UODs) which are knots, folds, and other interlacements of long polymer chains. These elements are formed at the precipitation of the polymer and are stable even in the polymer melt because of the great lengths of the polymer chains. In some cases, the elements unable to sorb the given compound may be transformed into the sorption centers for it. When present in the sorption center, antioxidant molecules cannot move and react with macroradicals participating in the polymer oxidation, which results in the dependence of the so-called critical antioxidant concentration on that of the sorption centers. The theory of the formation and reconstruction of UOD-based sorption centers is discussed. Formation of a polymeric substance may be divided into two stages: polymerization or polycondensation of low-molecular compounds and self-assembling of macromolecules into polymeric material. Opposite to numerous investigations of the first step of this process and of the properties of the end products, the stage of transition of the macromolecules into the polymeric material and possibilities of regulating its properties in this stage are usually neglected.