Convergent synthesis of siloxane starburst dendrons and dendrimers via hydrosilylation

New highly branched starburst dendrons and dendrimers containing siloxane linkages were convergently synthesized via hydrosilylation. Allyl cyanide and allylbis(4-(hydroxydimethylsilyl)phenyl)-methylsilane were used as the starting material and building block, respectively. The allyl group was a synthon of (N,N-diethylamino)silane, which was a suitable electrophilic silicon species. The starburst dendrons and dendrimers were constructed starting at the point which became the periphery of the molecule. The hydrosilylation of allyl cyanide with chlorodimethylsilane was carried out, followed by amination with diethylamine, and the resultant aminosilane was reacted with the building block to yield the first-generation dendron (G1) possessing two cyano groups. The next-generation dendron (G2) could be built up in a similar manner, as the hydrosilylation of the allyl group of G1 with chlorodimethylsilane, amination, and reaction with the building block. By repeating the procedure, G2, G3, and G4 dendrons possessing 4, 8, and 16 cyano groups were synthesized, respectively, which were purified by silica gel column chromatography. super(1)H and super(13)C NMR spectra were consistent with the structure of these dendrons. The molecular weights based on standard polystyrene measured by GPC were somewhat higher than those of the calculated values, and the narrow molecular weight distribution indicated the starburst polymers were reasonably pure. The Mark-Houwink constants K and alpha , calculated from the relationship between the molecular weight and the intrinsic viscosity of the polymers, were found to be 1.33x10 super(-3) and 0.45, respectively. The spherical starburst dendrimer was synthesized by the reaction of the aminosilane intermediate of G3 with tris(4-(hydroxydimethylsilyl)phenyl)-methylsilane having three reactive hydroxy groups. The glass transition temperatures (T sub(g)) of these polymers were from -61 to +36 degree C, where the larger generation molecule had higher T sub(g).