Local Conformation of Regular Star Polymers in a Good Solvent: A Monte Carlo Study

Abstract

Off-lattice Monte Carlo simulations were performed on linear and 12-arm regular star polymers with up to 472 repeat units in the excluded-volume regime. For both topologies, the overall size scales asymptotically with molecular weight through a Flory exponent, v = 0.588, but for finite molecular weights, the apparent exponent is slightly different in the case of the radius of gyration and of the root-mean-square end-to-end distance and definitely smaller in the case of the hydrodynamic radius. The interatomic distances within the star follow a 2-fold behavior, according to whether the two atoms belong to the same arm or to different arms. This result is related with the peculiar behavior of the scalar products among the bond vectors. If these belong to the same arm and are remote from the branch point, the scalar products follow the same pattern as in the linear chain. If however the bonds are close to the branch point, the scalar products are much larger and essentially constant, indicating a substantial arm stretching. Conversely, if the two bonds are on different arms, the scalar products across the branch point drop at once by more than 1 order of magnitude. Therefore, the initial arm directions are essentially noncorrelated, and the interarm repulsions are best accommodated with a minimum entropy loss.