Investigation of the crossover from simple liquid-like to a polymer-like behavior of polyisoprene by means of MD simulations

摘要

The crossover from small-molecule to polymer behavior in realistic models of PI at temperatures well above the glass transition is investigated by means of MD simulations. The molar masses range from the monomer to M?_w = 6 800 g · mol~(-1) which is far from the critical value for entanglement in PI. It is shown that at this temperature the non-Gaussian parameter almost vanishes in the Q-range studied. This implies Gaussian behavior in almost all the Q-range. From the mean square displacement and the incoherent scattering function behavior a smooth transition from the microscopic regime to the Rouse dynamics is observed. The Rouse behavior is achieved at chain molecular weights of about 1000 g · mol~(-1), which corresponds to 14 monomer units.