Full Paper: A new model for ultrasonic scission of polymer chains has been developed. The model takes the coiled nature of the polymer chains into consideration. the time evolution of the molecular weight distribution for several values of the solvent quality parameter is obtained using the new model. It is seen that the model leads to higher scission rates and lower final molecular weights for better solvents in accord with the experiments. Simulated gel permeation chromatography results are also in line with the experiments.