Architecture and Conformation of Uncharged and Charged Hyperbranched Polymers: Computer Simulation and Mean-Field Theory

HBP Builder: A Tool to Generate Hyperbranched Polymers and Hyperbranched Multi-Arm Copolymers for Coarse-grained and Fully Atomistic Molecular Simulations

Computer simulation has been becoming a versatile tool that can investigate detailed information from the microscopic scale to the mesoscopic scale. However, the crucial first step of molecular simulation is model building, particularly for hyperbranched polymers (HBPs) and hyperbranched multi-arm copolymers (HBMCs) with complex and various topological structures. Unlike well-defined polymers, not only the molar weight of HBPs/HBMCs with polydispersity, but the HBPs/HBMCs with the same degree of polymerization (DP) and degree of branching (DB) also have many possible topological structures, thus making difficulties for user to build model in molecular simulation. In order to build a bridge between model building and molecular simulation of HBPs and HBMCs, we developed HBP Builder, a C language open source HBPs/HBMCs building toolkit. HBP Builder implements an automated protocol to build various coarse-grained and fully atomistic structures of HBPs/HBMCs according to user's specific requirements. Meanwhile, coarse-grained and fully atomistic output structures can be directly employed in popular simulation packages, including HOOMD, Tinker and Gromacs. Moreover, HBP Builder has an easy-to-use graphical user interface and the modular architecture, making it easy to extend and reuse it as a part of other program.

Where are the End-Groups in a Hyperbranched Polymer?

The location of the end-groups in hyperbranched polymers is modelled by considering two synthetic strategies. The first synthesis is to make linear chains, and then link these chains. The second strategy is to sequentially add multifunctional monomers. The first strategy represents hyperbranched polymers synthesized by living radical methods, whereas the second represents polycondensations at low conversion. The high-conversion case is also considered. The present analysis suggests that sequential addition of monomers places more end-groups at the polymer’s surface than synthesis by linking chains. If the end-groups are catalysts, synthesis by the addition of monomers should give fewer inaccessible catalysts.

Models for randomly hyperbranched polymers: Theory and simulation

We derive theoretical models for the structures of randomly hyperbranched polymers in solution, and test them against computer simulations. The models are based on the same basic approach: Building a structure by the random assembly of "simple units," which may be monomers, linear chains, or larger branched species. Comparisons to simulation reported here show that the conformations of hyperbranched species, i.e., their radii of gyration and full density profiles, are accurately described by this approach. These stringent tests complement previous tests against experiment. We include the effects of solvent quality at the mean-field level. Our model works best for hyperbranched structures, but also reproduces very well the simulated density profiles of dendrimers. The models reported here provide a simple, but realistic, picture of the physical influences that affect the conformations of hyperbranched species.

Structural effects in overcharging in complexes of hyperbranched polymers with linear polyelectrolytes

New insight is provided by a combined theoretical and simulational approach regarding the effects of structural characteristics of the constituents, on the overcharging phenomena in complexes formed by hyperbranched polymers with linear polyelectrolytes.

Randomly hyperbranched polymers

We describe a model for the structures of randomly hyperbranched polymers in solution, and find a logarithmic growth of radius with polymer mass. We include segmental overcrowding, which puts an upper limit on the density. The model is tested against simulations, against data on amylopectin, a major component of starch, on glycogen, and on polyglycerols. For samples of synthetic polyglycerol and glycogen, our model holds well for all the available data. The model reveals higher-level scaling structure in glycogen, related to the beta particles seen in electron microscopy.