Abstract
A comparative analysis of intramolecular dynamics of four types of isolated dendrimers from the fourth to the seventh generations belonging to the siloxane and carbosilane families, differing in spacer length, core functionality, and the type of chemical bonds, has been performed via atomic molecular dynamics simulations. The average radial and angular positions of all Si branching atoms of various topological layers within the dendrimer interior, as well as their variations, have been calculated, and the distributions of the relaxation times of their radial and angular motions have been found. It has been shown that the dendrons of all the dendrimers elongate from the center and decrease in a solid angle with an increasing generation number. The characteristic relaxation times of both angular and radial motions of Si atoms are of the order of a few nanoseconds, and they increase with an increasing generation number and decrease with temperature, with the angular relaxation times being larger than the radial ones. The relaxation times in the carbosilanes are larger than those in the siloxanes. The rotational angle dynamics of the carbosilane dendrimers show that the chain bending is mainly realized via trans-gauche transitions in the Si branching bonds.
Highlights
Dendrimers are hyperbranched molecules with a regular structure [1,2,3]
We focus on the comparative study of the dynamics realized in single siloxane and carbosilane dendrimer molecules of the fourth to the seventh generation
A full-atomic molecular dynamics simulation of the siloxane and carbosilane dendrimers from the fourth up to the seventh generation was carried out to examine the effects of the chemical nature of the bonds, the spacer lengths, and the core functionality on the intramolecular dynamics
Summary
Dendrimers are hyperbranched molecules with a regular structure [1,2,3]. Their behavior is unique due to the specific organization of their molecular structure, high monodispersity, and high functionality. It is expected that the tree-like molecular morphology of dendrimers would distinguish their behavior from that of conventional linear polymers. A number of novel unusual phenomena has recently been observed in dendrimer melts that do not have any strict fundamental description. One such phenomenon is an unprecedented jump in the viscosity of high-generation carbosilane dendrimer melts [31]. It has been found that while low-generation dendrimer melts
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