Small-angle x-ray scattering from dilute solutions of substituted phthalocyaninato-polysiloxanes

Abstract

The dilute-solution properties of alkoxy-substituted phthalocyaninato-polysiloxanes are investigated by using small-angle X-ray scattering (SAXS). The scattering of rodlike particles is studied with special emphasis on molecular parameters important in real polymeric systems such as polydispersity, overall length, finite cross-section, and chain flexibility. Polydispersity and finite flexibility show a strong interdependence with opposite influence on the particle scattering factor. It is shown that especially in the limit of high persistence lengths (rod limit) polydispersity plays a crucial role in determining molecular dimensions by scattering techniques. The exact form factor for a polydisperse, circular cylinder is compared to the approximate form factor for infinitely thin rods corrected for a finite cross-section. Good agreement is found in the angular range from h = 0.05 to 0.1 The Zimm analysis of the experimental data obtained from dilute solutions in heptane and toluene gives weight-average degrees of polycondensation typically between 50 and 160. While the fit of the radius of gyration as a function of the contour length only allows for the estimation of a lower limit of lo00 8, for the persistence length, the angular dependence of the scattered intensity agrees well with particle scattering functions of polydisperse, thick rods. Radii of gyration of the cross-section are determined to range typically between 10 and 25 8, while the polydispersity is in good agreement with a most probable distribution (M,/M,, -1 = 1). The experimental mass per unit contour length is well within the range of the theoretical values, indicating the absence of aggregation in the concentration regime investigated. Besides the conventional Zimm extrapolation, which is nonlinear for rodlike particles, several linear methods arising from the asymptotic scattering behavior of rodlike particles are discussed and applied to the experimental data after elimination of the cross-section factor. Data from both treatments show a good agreement and moreover confirm the rodlike chain conformation of the polymers.

Hexagonal-columnar mesophases in substituted phthalocyaninatopolysiloxanes

“…Of course such a feature is not expected because of the considerable polydispersity of the polymer samples, which is of the order of MJMn = 2. 4 The arrangement of monomer units along the single polymer backbone, which is the only register in the c direction, should not give rise to any intermolecular correlation. The absence of positional correlation in this direction, however, does not imply that there is a reduced dimensionality of molecular orientational distribution which is found experimentally in Langmuir-BIodgett films from C1C8PCPS.8…”

“…This is assumed to be the major reason for the fact that in this case no aggregation phenomena are observed in dilute solution. 4 It is anticipated that these differences in molecular architecture also influence the phase behavior in the bulk.…”

Polyphenylene Nanostructures

“…313,314 Interestingly, it could be shown that the same approach was successful for hairy rods as well. 26,[315][316][317][318][319][320][321][322][323] Thereby, hairy-rod PPPs were transferred in single layers by each dipping and undipping. Orientation of the rods occurs in the dipping direction, thus giving rise to anisotropic multilayers.…”

Nanocomposites of Hairy‐Rod Macromolecules: Concepts, Constructs, and Materials

“…[13][14][15][16][17][18][19][20] The synthesis of these interesting polymers was substantially improved by Caseri and Sauer; [14,16,17] and according to their work large degrees of polymerization can be reached. The close cofacial packing of the monomer units along the polysiloxane chain which is sketched in Figure 2 leads to a strong interaction between repeat units and results in a Si-O-Si bond angle of 1808.…”