Local Dynamics and Hydrogen Bonding in Hyperbranched Aliphatic Polyesters

We report results from fully atomistic molecular dynamics simulations of commercially available aliphatic hydroxyl-terminated hyperbranched polyesters of two different architectures/sizes in the bulk, exploring dynamic mechanisms associated with their physical behavior as it has been described by pertinent experimental techniques. Particular emphasis is given on the role of the hydrogen-bonding capabilities of the examined systems and the impact on their local dynamic response. Analysis of the simulation results reveals that certain key aspects of their unique behavior, such as the molecular weight dependence of local group reorientation as well as the more restricted motion of these moieties in low-generation polyesters, can be explained by considering the distinct hydrogen-bonding pattern, which is realized at the intra- and intermolecular levels. This interconnection is shown to be realized through a coupling mechanism of local bond relaxation with the time scale pertinent to the formed hydrogen bond network. Quantitative accounts are provided for the relative percentage of the different kinds of hydrogen bonds as well as for their corresponding lifetimes. The detail afforded by the present work provides new insight into the structure/properties relation of such molecules and offers new ground for the interpretation of relevant experimental findings.