Polymacromonomers: Dynamics of dilute and nondilute solutions

Polymacromonomers (PMs) are a class of branched polymers whose global shape depends strongly on the degree of polymerization of the backbone and the length of the side chain. As opposed to their equivalent linear chains, PMs can indeed adopt spherical, cylindrical, or wormlike shapes. Other parameters such as the rigidity of the side chain, the distance between branches and the interactions (incompatibility) between the backbone and the branches can also contribute to the global morphology of the PMs. In this work we describe the dynamical behavior of several poly(ω-norbornenyl polystyrene) differing by their backbone and their side chain lengths, in dilute and nondilute ranges of concentration, using dynamic light scattering and viscosity experiments. The results obtained, using both techniques, suggest dense and nonentangled particles as revealed by the low viscosity values and the scaling laws observed for the variation of the diffusion coefficient as a function of the molar mass and the concentration c. The transition from dilute to nondilute regime is characterized by an abrupt increase of the diffusion coefficient with the concentration, as opposed to the case of linear and flexible polymer coils. Above this concentration, the diffusion coefficient is independent of the molar mass and hardly varies with the concentration. It is identified as reflecting the overall collective motion of the branches. This transition is also observed in the variation of the reduced viscosity n_sp/c as a function of c. Similar studies have been carried out on star polymers of roughly same molar mass where no such an abrupt transition was observed.