Hybrid Polycarbosilane-Siloxane Dendrimers: Synthesis and Properties

Sergey A Milenin,Viktor G Vasil’Ev,Sergey N Chvalun,Eleonora V Shtykova,Nikolay K Balabaev,Aziz M Muzafarov,Lev A Feigin,Maxim V Petoukhov,Elizaveta V Selezneva,Pavel A Tikhonov,Andrey O Kurbatov,Elena A Tatarinova,Elena Yu Kramarenko,Alexander I Buzin

doi:10.3390/polym13040606

Abstract

A series of carbosilane dendrimers of the 4th, 6th, and 7th generations with a terminal trimethylsilylsiloxane layer was synthesized. Theoretical models of these dendrimers were developed, and equilibrium dendrimer conformations obtained via molecular dynamics simulations were in a good agreement with experimental small-angle X-ray scattering (SAXS) data demonstrating molecule monodispersity and an almost spherical shape. It was confirmed that the glass transition temperature is independent of the dendrimer generation, but is greatly affected by the chemical nature of the dendrimer terminal groups. A sharp increase in the zero-shear viscosity of dendrimer melts was found between the 5th and the 7th dendrimer generations, which was qualitatively identical to that previously reported for polycarbosilane dendrimers with butyl terminal groups. The viscoelastic properties of high-generation dendrimers seem to follow some general trends with an increase in the generation number, which are determined by the regular branching structure of dendrimers.

Highlights

Dendrimers as a new form of a polymeric substance continue to attract the considerable attention of researchers due to a unique set of chemical and physical properties resulting from their regular tree-like architecture [1,2,3,4,5]
A comparative analysis of a number of physical properties of these dendrimers with the properties of pure carbosilane dendrimers, as well as dendrimers with some other end groups, made it possible to deepen our understanding of the influence of peripheral layers and the generation numbers on the conformational behavior and intermolecular interactions of carbosilane dendrimers
It was confirmed that Tg of highgeneration dendrimers hardly depends on the generation number, but it is strongly affected by the chemical nature of the peripheral layer

Summary

Introduction

Dendrimers as a new form of a polymeric substance continue to attract the considerable attention of researchers due to a unique set of chemical and physical properties resulting from their regular tree-like architecture [1,2,3,4,5]. Intensive experimental and theoretical research has demonstrated that the dualism of the dendrimer nature, expressed in its definition as a macromolecule-particle [6,7], has objective grounds. The term particle is associated with the early visualization of the dendrimer shape being close to spherical [8,9], but mainly with the viscosity of their dilute solutions that obeys Einstein’s equation, depending only on the volume fraction of the solute, but not on its molecular weight [5], as well as SAXS data, which are best described by models of monodisperse spherical objects [10,11,12]. Computer simulations have confirmed the soft molecular nature of dendrimers, demonstrating their internal “life” in dynamics [10,19,20,21,22,23]

Methods

Discussion

Conclusion