In contrast to part 1-3 of the series this publication deals with the reaction behavior of the TESPT sulfur chain. The influence of important rubber chemicals on the reaction behavior of the tetrasulfane group using suitable model systems will be investigated with the aid of modern analytical methods. It can be shown with reference to selected rubber technical tests, that the chosen test conditions relate to practical applications. These were confirmed during the development of a new silane especially for use in highly filled tread compounds using silica as filler.