Small-angle neutron scattering of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers

Abstract

Small-angle neutron scattering was used to characterize the structure of arborescent polystyrene-graft-poly(2-vinylpyridine) copolymers dissolved in methanol-d4 (CD 3 OD). A radial density profile based on a power law functional form provided a good fit to the scattering data. While a model with homogeneous density profiles in the core and shell, respectively, and with a size distribution (a polydisperse core -shell model) also fits the data comparably well, the extra parameters required for this fit are difficult to justify on the basis of the data. In addition, unconstrained fits using the core -shell model failed to converge to values of the overall molecular size and molecular weight which agreed with values determined from independent light scattering measurements which leads to the conclusion that the power law model is a more appropriate function for describing the radial density function of these molecules. The density profile from either model showed that the polystyrene core of the molecules is not collapsed. Values of the second virial coefficient, A 2 ; have been calculated from Zimm plots and it was found that A 2 decreased as a function of generation to close to zero for the highest generation (i.e. highest molecular weight) polymers. Finally, it was found that the radius of gyration of the polymers increases with the molecular weight according to the scaling relationship, R g , M v w with v ¼ 0:24^0:04: q

Conformation of Arborescent Polymers in Solution by Small-Angle Neutron Scattering: Segment Density and Core−Shell Morphology

“…The question of the presence of a thick core-shell interfacial region rather than a well-defined core phase, due to the random distribution of branching points within arborescent polymer molecules, was also considered previously. 11 This result clearly shows that the core mostly consists of PS and the shell of PS-d. The relatively higher values of the density profile for the G3 core region as compared to G4 shown in Figure 7c indicates that the PS-d of higher SLD penetrates the core region more deeply.…”

“…The excess SLD profiles obtained by deconvolution of the PDDF agree with the polymer density profile calculated by fitting the SANS data with a form factor corresponding to a shape where F(r) is maximum at the center of a molecule and decays as a function of r (the radial distance from the center of the molecule) according to a power law function. 10,11 For arborescent polymers, branching points are uniformly distributed throughout the molecule as the branching density increases. In contrast to the random and uniform distribution of branching points of arborescent polymers, a dendrimer has the same branching functionality as the monomer units at the end of the previous generation.…”

Determination of branch fraction and minimum dimension of mass-fractal aggregates

“…where z br is the number of primary particles in an average branch. The situation can become fairly complicated if multiple generations of branching occur in a hierarchical structure such as an arborial or dendric polymer [37]. Nonetheless, the branch fraction, Eq.…”

“…A number of examples of branched aggregate and polymer scattering measurements and simulations exist in the literature for example, [10,11,21,37,39,[41][42][43][44]. However, since Eqs.…”

Monomolecular films of arborescent polystyrene–graft–poly(2-vinylpyridine) copolymers: Precursors to nanostructured carbon materials

“…The AGP used in the current investigation was a copolymer consisting in an arborescent PS core and a large number of covalently bonded P2VP chains forming a shell (arborescent PSgraftP2VP), depicted as unimolecular micelles in Figure 1a [4]. The solution properties of arborescent PSgraftP2VP copolymers have been investigated extensively [5], but structural investigations of these unimolecular micelles in films have not yet been performed.…”