Core/shell hybrid dendrimers: Controllable rigidity determines molecular behaviour

Abstract

The hybrid dendrimers (HDs) composed of flexible carbosilane interior and rigid aromatic shell were developed for the first time by Diels - Alder cycloaddition of pre-synthesized carbosilane dendrimers and aromatic cyclopentadienones to elucidate the correlation between the dendrimer structure and its thermal and phase behaviour. There was found that thermal behaviour of HDs was dramatically different from that of entirely rigid phenylene dendrimers or flexible carbosilane dendrimers. The presence of rigid blocks as a periphery layer in the carbosilane dendrimers leads to a significant increase of a glass transition temperature, indicating increased rigidity of the whole dendrimer. To gain further insights into interrelation of structure and properties of HDs, the vice versa dendrimer with a rigid core and a flexible shell was synthesized via a copper catalyzed “click” reaction of ethynyl terminated polyphenylene dendrimer and the azide focal point functionalized carbosilane dendron. Unlike the flexible core/rigid shell dendrimers, this dendrimer demonstrated a polycrystalline behaviour that was confirmed by DSC and WAXS. We believe the approaches developed may allow for controllable syntheses of dendritic core-shell structures with desired morphology and thermophysical properties.