The number of impacts is increased with the 2 mm grinding balls due to the higher number of balls at same filling level. At 430 rpm, the grinding balls have a higher kinetic energy, which is crucial for a reaction to take place. The product of the number of impacts and the probability of reaction is highest for 2 mm grinding balls and decreases for larger grinding balls due to the large difference in the number of impacts. At 350 rpm, on the other hand, the probability of reaction decreases due to the reduced energy input. The 4 mm grinding balls have the highest kinetic energy, but the lowest number of impacts. The situation changes for 2 mm and 3 mm grinding balls, where the number of impacts increases but the probability of reaction decreases. The result is an approximately equal product of the number of collisions and the reaction probability, which leads to comparable oligomer fractions. The lower weight average molecular weight of the experiments with 6 % acid content at 350 rpm is striking (Table ). Due to the increased acid content, the reaction rate also increases and shorterchain oligomers are formed. The acidity has the greatest influence on the molecular weight here.