The melt viscosity of dendritic poly(benzyl ether) macromolecules

The zero shear melt viscosity, η₀, for a variety of dendritic poly(benzyl ether) macromolecules has been measured. The viscosity of low generation dendrimers exhibits a strong molecular mass, M, dependence, yet, direct proportionality between η₀ and M is observed at higher generations. The viscosity scales with M for mono- and tridendrons rather than generation number. Hypercore dendrimers continue this scaling although the viscosity is slightly greater. A large deviation from the master curve for the mono- and tridendrons is found for an end-substituted monodendron. The viscosity for the end-substituted monodendron is also much more temperature dependent than virgin dendrimers, and it is concluded that end groups have a much larger effect on the viscosity than the core. Reexamination of literature data for intrinsic viscosity and glass transition temperature is performed, and these quantities also scale with molecular mass. Comparison with free volume theory indicates that the theory is extremely robust although some question of its validity is made when applied to dendrimers.