Molecular weight distributions from size separation data for hyperbranched polymers

Size-separation characterization techniques such as size-exclusion chromatography separate polymers by hydrodynamic volume, not molecular weight; this makes it impossible to directly obtain the true molecular weight distribution, because each elution slice at a given hydrodynamic volume contains a range of molecular weights (“local polydispersity”). Simulations are used to show that, for randomly hyperbranched polymers, this spread of molecular weights is narrow for all except very low molecular weights. To a good approximation, size-exclusion techniques give the actual molecular weight distribution for hyperbranched polymers. This applies to synthetic polymers such as polyglycerol, the natural polymer glycogen, and others.