Hydrodynamic Characteristics and Conformational Parameters of Ferrocene-Terpyridine-Based Polymers

Abstract

Nowadays, the study of metallopolymers is one of the fastest growing areas of polymer science. Metallopolymers have great potential for application in multiple technological and various biomedical processes. The macromolecules with the possibility of varying the number and type of metal ions along the entire length of the polymer chain are of particular interest. In this regard, this study presents results on two successfully synthesized homopolymers, random and block copolymers based on PMMA, containing ferrocene and terpyridine moieties in the side chain. Different architectures of copolymers may attribute interesting properties when creating complexes with various metal ions. A detailed hydrodynamic study of these structures was carried out, the consistency of hydrodynamic data was established using the concept of a hydrodynamic invariant, the absolute values of the molar masses of the studied objects were calculated, and the conformational parameters of macromolecules were determined. Using the Fixman-Stockmayer theory, the equilibrium rigidities of the studied systems were calculated and the relationship between the chemical structure and conformational characteristics was established. The studied copolymers can be attributed to the class of flexible-chain macromolecules. An increase in the equilibrium rigidity value with an increase of the side chain, which is characteristic of comb-shaped polymers, was determined.

Keywords: analytical ultracentrifugation; complexation; equilibrium rigidity; light scattering; metallopolymers; polymer chain conformation.

Figure 1

Schematic representation of the synthesis of four Fc- and/or tpy-containing polymers.

Figure 2

Normalized SEC curves of the four polymers (eluent: CHCl₃/isopropanol/NEt₃ in a 94:2:4 volume ratio).

Figure 3

(a) The normalized specific viscosity, η_sp/c, vs. concentration, c, obtained for the studied polymers in THF (open symbols) and DMF (filled symbols) at 20 °C. (b) The dependence of Δρ = ρ − ρ₀ on the polymer concentration, c, determined for poly(Fc) and (Fc)-co-(tpy) at 20 °C.

Figure 4

Normalized c(s) distributions vs. intrinsic sedimentation coefficients [s] resolved with Sedfit for the poly(Fc) sample in different solvents (a) and all of the studied polymers in THF solutions (b). The presented distributions correspond to the lowest studied concentration of the systems, and the concentration values are indicated in the figure. All AUC runs were performed at 20 °C.

Figure 5

The normalized distributions of weight component concentration, w/w_max, over hydrodynamic radii, R_h, obtained with DLS for the studied polymers (poly(Fc), poly(tpy)) and copolymers ((Fc)-co-(tpy), (Fc)-bl-(tpy)) in THF solutions. All data were obtained at 20 °C. The diffusion coefficients, D₀, at the infinite dilution limit are presented in Table 3.

Figure 6

The application of Fixman–Stockmayer theory to the hydrodynamic data based on already published PMMA data [50,79,80] (solid lines and open circles) and its comparison with the studied samples (dashed lines and open squares).