Manipulation of Hyperbranched Polymers' Conformation

The hydrodynamic volume for a series of hyperbranched polymers was studied to determine the volume change in a variety of solvents. The chemically different interior core and branching units were found to readily expand and contract by a factor of 2 creating large or small free volume, respectively. Furthermore, a solvent that maximally swells the polymer created a viscosimetric (hydrodynamic) radius which changed linearly with molecular mass. This is contrary to what is expected for dendrimers where the radius has been shown to scale with ln( M ). A model was developed to account for the effect of molecular mass polydispersity on the intrinsic viscosity (viscosimetric volume), since hyperbranched polymers are polydisperse in nature, and it was found that this did not affect the observation. Solvents that contracted the hyperbranched polymers showed a complicated hydrodynamic radius scaling with mass. It was generally concluded that these polymers readily change volume with solvent effects important in influencing the change. Further results with a similar hyperbranched polymer having alkane rather than hydrogen end groups revealed a polymer that did not swell or contract as much (10% variation) for a wide range of solvents. In addition, this polymer had lower overall free volume and was found to behave in a manner that was quite similar to sterically stabilized particles. Thus, the core−shell molecular morphology, as well as its utility, depends quite strongly on the end groups and rational design of hyperbranched molecules must consider thermodynamic interactions with the solvent and within the molecule itself.