The covalent grafting of poly (sodium 4- styrene sulfonate) on poly (ϵ-caprolactone) was proved to enhance the bioactivity of this polymer. The aim of this article was to perform kinetic studies of the activation and grafting processes and illustrate the influence of several parameters on the grafting rate and on the degradation of the polymer substrate. Results showed that the active groups created on poly (ϵ-caprolactone) surface by ozonation reach a maximum concentration after a short exposure time. Moreover, a kinetic study of poly (sodium 4- styrene sulfonate) grafting on poly (ϵ-caprolactone) substrate showed that the activation energy of this process was low and the influence of conditions such as pH, monomer concentration, time reaction and grafting temperature was deeply significant for the outcome of the treatment. Besides, ozone oxidation and thermal grafting lead to surface degradation, under certain conditions, for example in the presence of Mohr's salt used as a catalyst to enhance grafting rate. The whole study illustrates that ozone-induced grafting is a strong instrument for surface functionalization, although its parameters should be wisely studied and carefully selected. Poly (sodium 4- styrene sulfonate) functionalization improves bioactivity of poly (ϵ-caprolactone) while decreasing the slowness of its biodegradation.