Polymacromonomers: Structure and dynamics in nondilute solutions, melts, and mixtures

Polymacromonomers are viewed as a special class of well-characterized branched polymers with high density of arms and shape ranging from spherical to nonspherical, depending on the arm functionality and molecular mass. We synthesized a series of such model systems with polystyrene or poly(methyl methacrylate) backbone and varying functionality and/or molecular mass of polystyrene arms and investigated their structure and dynamics in nondilute solutions (well above the overlapping concentration c*) and in the melt. We found similarities in their soft ordering and dynamic response with other well-known model branched polymers such as multiarm stars, in that cooperative and selfdiffusion or arm relaxation and structural rearrangements control their dynamics in solution or in the melt; respectively. However, the present systems do not follow the scaling laws of stars as a consequence of their anisotropy and the larger interpenetration needed to observe the effect of ordering on the dynamic response. The use of blends consisting of different polymacromonomers essentially enhances the polydispersity, enabling the detection of the self-diffusion mode in analogy to the multiarm stars, as well as obtaining a wide range of effective intermediate molecular masses, depending on composition. The mixtures investigated were miscible at all times and exhibited a dynamics dominated by the response of the slower components. These polymers complement the generic physical picture of the dynamics of branched polymers toward the low arm molecular mass.