Molecular shape of regular star polymers by Monte Carlo simulations

Off-lattice Monte Carlo simulations were performed on linear and 12-arm star polymers in a good-solvent and in the Theta state to investigate both the molecular shape and the size distribution. We find that in a good solvent the star polymer is more spherical than a random walk, the more so the smaller its size is; moreover, a star of finite chain length in the Theta state has a shape more similar to that in good solvent than to that in a random walk because of the excluded-volume restrictions that are particularly relevant in the core region. Both results are at variance with what is found in linear chains. Furthermore, the size distribution of the star is much narrower in a good solvent than in a random walk, approaching somewhat a delta function. This effect is also seen in the strong deformation of the density profile away from the center of mass.