Investigations of the structure and conformations of star-shaped polymers with fullerene branching centers: Polystyrenes with different structures and functionalities of the C$_{60}$ centers in toluene

The structure of regular star-shaped polystyrenes in deuterated toluene with single (C$_{60}$) and double (C$_{60}$–C$_{60}$) branching centers and different numbers of arms ($f$ = 6, 12, 22) has been investigated using small-angle neutron scattering. For functionalities $f$ = 6 and 12, the thermodynamic rigidity and sizes of arms are larger than the corresponding characteristics of the linear polystyrene precursor; however, for $f$ = 22, the situation reverses: the flexibility increases, the arms are compressed, and the radius of gyration of the stars decreases. The stars transform into dense spherical aggregates, the behavior of which is inconsistent with the Benoit and Daoud–Cotton theories for structures with a high functionality and Gaussian arms. This is explained by the competition between the structuring effect of the fullerene branching center on the solvent and by the reverse effect of the arms playing the role of defects in an ordered layer of the solvent around the fullerene.