Effects of PEGylation on the Size and Internal Structure of Dendrimers: Self-Penetration of Long PEG Chains into the Dendrimer Core

G4 PAMAM dendrimers grafted with poly(ethylene glycol) (PEG) of different sizes (Mw = 550 and 5000) and grafting densities (12−94% of surface terminals) were simulated using the coarse-grained (CG) force fields previously developed and reparametrized in this work. Simulations are carried out for G4, G5, and G7 un-PEGylated dendrimers that are either unprotonated, terminally protonated, or protonated on both terminals and interior sites, corresponding to pH values of >10, 7, and <5, respectively. As protonation increases, simulations show only a small (∼6% for G4 and G5) change of dendrimer radius of gyration Rg and show a structural transition from dense-core to dense-shell structure, both of which are in agreement with recent scattering experiments and all-atom simulations. For the PEGylated dendrimers, the Rg of the fully PEG(Mw = 5000)-grafted dendrimer also agrees well with experiment. Longer PEG chains with higher grafting density yield PEG−PEG crowding, which stretches dendrimer terminals toward wat...