Backbone stretching of wormlike carbosilane dendrimers

Wormlike dendrimers made of flexible and noninteracting segments were synth esized. Starting from a poly(methylhydrosiloxane) G(0) and using short prop ylsilane branches, the synthesis did not go beyond the second generation, a s predicted from steric congestion. The starting polymer and the G(1) and G (2) dendrimers synthesized were studied by small-angle neutron scattering. The molecular-weight dependence of their radius of gyration (R-g proportion al to M-nu, nu growing from 0.53 for G(0) to 0.94 for G(2)) showed the back bone conformation to go from very flexible for G(0) to nearly rodlike for G (2). This was supported by the growth of the persistence length from 12 to over 200 Angstrom, as deduced from an analysis of the data according to Ben oit-Doty's law. The dendrimers being made of flexible parts, their stretchi ng was attributed to the congestion of the peripheral branches. The absence of liquid crystallinity was imputed to the dynamical flexibility of the mo lecules.