Morphology and organization of poly(propylene imine) dendrimers in the melt from molecular dynamics simulation

Molecular dynamics simulations are performed on generations 2 (G2) through 5 (G5) of poly(propylene imine) dendrimers at 400 K in order to investigate characteristics of molecular structure and morphology in the melt. As the generation increases, the dendrimers assume a more spherical shape, and the degree of dendron overlap increases, albeit at a decaying rate. The distribution of end groups within the molecule widens with G and separates at G5 into inner (back-folded), intermediate, and outer rims. Back-folded branches are accommodated by the increased extension of the initial spacers. Furthermore, the radius of gyration scales approximately with the cubic root of the number of monomers. Finally, interpenetration of individual dendrimer molecules decreases with generation. Simulation results are in good agreement with the limited experimental data available.