Topological constraints, density heterogeneities and mixing play a crucial role in the dynamics of soft materials. An important consequence the ability to tailor the flow properties of different systems at molecular level, by accounting for microstructural characteristics and thermodynamics. To illustrate this point, we present 2 examples: (i) High-molar mass star polymers with changing functionality can respond as regular entangled stars or prototype soft colloids either in solution or in melt. In solution, they exhibit intriguing properties and their (ultra)softness is responsible for a variety of new metastable states and transitions at high fractions in molecular or polymeric solvents. We discuss here the rich state diagram of large stars and small hard spheres. (ii) Adding small fraction of ring polymers with low viscosity to linear polymers with higher viscosity results in a mixture with enhanced viscosity compared to both components. These examples demonstrate that polymer chemistry and thermodynamics hold the premise for exploring and understanding novel properties of soft matter.