A. S. Gubarev

Conformations of sodium poly(styrene-4-sulfonate) macromolecules in solutions with different ionic strengths

Translational friction and viscosity of dilute solutions of sodium poly(styrene-4-sulfonate) with molecular masses of M = (5 × 104)−(85 × 104) are studied at different concentrations of low-molecular-mass salts. Molecular masses of the polymer are determined from the sedimentation-diffusion data. The study of the correlation between molecular masses and hydrodynamic characteristics resulted in ascertainment of the Kuhn-Mark-Houwink-Sakurada relationships for salt-free aqueous solutions of the polymer and solutions of the polymer in 0.2 M NaCl, 4.17 M NaCl, and 1.0 M KCl. It is shown that, as the ionic strengths of solutions are varied from minimum (H2O) to maximum (4.17 M), macromolecules of the strong polyelectrolyte sodium poly(styrene-4-sulfonate) change their conformations from rigid rods to coils and, then, approach a globular conformation. In terms of the Gray-Bloomfield-Hearst and Yamakawa-Fujii theories and within the framework of the weakly bent cylinder model, the statistical Kuhn segment length and the hydrodynamic diameter of sodium poly(styrene sulfonate) chains are estimated in 0.2 and 4.17 M NaCl, 1.0 M KCl, and salt-free aqueous solutions. The electrostatic component of the equilibrium rigidity is taken into account within the framework of the Odijk-Fixman-Skolnick and Dobrynin theories.

Additive poly[3-(trimethylsilyl)tricyclononene-7]: Molecular properties and chain rigidity

With the use of the methods of hydrodynamics, the Kerr electrooptical effect, and dielectric polarization in solution, the molecular properties of a homologous series of poly[3-(trimethylsilyl)tricyclononene-7] samples synthesized via additive polymerization have been studied. Scaling relationships that describe how the intrinsic viscosities, diffusion coefficients, and sedimentation coefficients of macromolecules depend on their molecular masses in toluene at 298 K have been obtained. It has been shown that the additive poly[3-(trimethylsilyl)tricyclononene-7] has enhanced kinetic chain rigidity. According to hydrodynamic data, the length of the Kuhn segment for this polymer does not exceed 6.0 ± 0.6 nm, while the kinetic fragment estimated from electrooptical data is 4.3 nm. In terms of kinetic properties, the studied polymer is similar to wellknown poly[1-(trimethylsilyl)-1-propyne], with the specific morphology of its highly permeable films being determined by the large-scale mechanism of chain orientation.

Influence of the length of side substituents on optical and electro-optical properties of polydialkoxyphosphazenes

The electro-optical and dynamo-optical properties of dilute solutions of polydialkoxyphosphazenes with different lengths of side substituents are studied. Sign inversion of the specific Kerr constant and of the reduced flow birefringence for the number of carbon atoms in side aliphatic chains, m, varying from 3 to 7 is ascertained. The anisotropy of optical polarizability of a monomer unit changes in the studied series of polydialkoxyphosphazenes. It attains the minimum values and changes its sign from positive to negative at m = 5–6. The resulting data provide an explanation for the mesomorphism of these polydialkoxyphosphazenes, which is connected with the possibility of alternative orientation of monomer units.

Diffusion-viscometric analysis and conformational characteristics of sodium polystyrenesulfonate molecules

Samples of sodium polystyrenesulfonate of molecular weights varying in a 20-fold range were synthesized. The hydrodynamic behavior of the samples was studied in a 0.2 M NaCl solution in which the initial polyelectrolyte effects are suppressed. Relationships between the molecular weight and the translational friction coefficient and intrinsic viscosity were obtained. The theory describing the hydrodynamic behavior of wormlike chains with taking into account both the percolation effects and the excluded-volume effects was applied to estimation of the length of the statistical segment and the cross section of the sodium polystyrenesulfonate molecules in 0.2 M NaCl solution.

Linear poly(ethylene imine)s: true molar masses, solution properties and conformation

In-depth characterization of pharmaceutically relevant polymers plays a pivotal role in many areas, including nanoscience, gene therapy, analytical and polymer chemistry etc. Notwithstanding substantial efforts spent in this area, there are still unresolved challenges and one of the most demanding problems is the determination of absolute molar masses of a broad range of biocompatible cationic polymers. Hereby, we present a combined analytical approach for a distinct and self-consistent characterization of a series of linear poly(ethylene imine)s (PEIs) consisting of six in-house prepared PEIs (0.9 kDa < Mtheor < 250 kDa) and three commercially available linear PEIs (Polyscience labeled as 2.5 kDa, 25 kDa, and 250 kDa). The polymers were studied, in 0.2 M NaBr methanol, by the methods of molecular hydrodynamics: analytical ultracentrifugation, intrinsic viscosity and translational diffusion measurements. Absolute values of the molar masses were evaluated by the classical sedimentation-diffusion analysis resulting in the following range: 1.1 kDa < M < 13.9 kDa. It was demonstrated that the molar masses reported by the manufacturer, as well as theoretical and/or molar masses evaluated by common SEC analysis, are significantly overestimated. The complete set of Kuhn–Mark–Houwink–Sakurada scaling relations shows linear trends over the whole range of the molar masses, whilst the determined scaling indices virtually correspond to the homologous series characterized by a coil conformation ([η] = 0.255 × M0.56; s0 = 0.015 × M0.48; D0 = 994 × M−0.52). The conformational characteristics of LPEI, i.e. equilibrium rigidity (the Kuhn segment length) and the diameter of the PEI chains, were evaluated for the first time and constitute A = 1.9 ± 0.6 nm and d = 0.4 ± 0.2 nm, respectively. The presented self-sufficient analytical approach covers an important area of thorough polymer characterization by nowadays alternative but fundamental hydrodynamic methods allowing for complete structural and molecular analysis of almost any macromolecules in solution.

Conformational properties of biocompatible poly(2-ethyl-2-oxazoline)s in phosphate buffered saline

Inspired by the increasing popularity of poly(2-ethyl-2-oxazoline) (PEtOx) for biomedical applications, this study reports the complete and thorough solution analysis of the homologous series of biocompatible PEtOx samples in a very broad range of molecular weights ranging from 11.2 × 103 g mol−1 up to 260 × 103 g mol−1. The main focus of the research was on the determination of the conformational properties of PEtOx macromolecules at a temperature of 37 °C in phosphate buffered saline (PBS) simulating the parameters of physiological media. The polymers were studied in PBS solutions by analytical ultracentrifugation, dynamic light scattering (DLS), translational diffusion, and intrinsic viscosity measurements in a temperature range from 15 °C up to 72 °C. The complete set of Kuhn–Mark–Houwink–Sakurada scaling relationships revealed linear trends over the whole range of the studied molar masses, while the determined scaling indices at 37 °C correspond to the coil conformation in a thermodynamically good solvent ([η] = 0.045 × M0.62, s0 = 0.010 × M0.46 and D0 = 1750 × M−0.54). Based on the intrinsic viscosity values (most sensitive characteristic to the size variations of polymer coils, [η] ∼ r3), it was demonstrated that PEtOx macromolecules in PBS solutions undergo a transition from swollen polymer coils with gradual deterioration of thermodynamic quality of solutions within the temperature range of 15–45 °C, reaching θ-conditions at 55 °C with further precipitation at 62–72 °C. Also, to the best of our knowledge, the conformational parameters (equilibrium rigidity/the Kuhn segment length and the diameter of the polymer chain) of PEtOx macromolecules were evaluated under physiological conditions for the first time and constitute A = 1.8 ± 0.3 nm and d = 0.7 ± 0.4 nm. These equilibrium rigidity values classify PEtOx as a flexible macromolecule with rigidity similar to that of poly(ethylene glycol). For the first time, we were able to demonstrate a direct influence of thermosensitivity on the rigidity of the biocompatible polymer: PEtOx. The Kuhn segment length is undoubtedly decreasing when approaching the LCST.

Amphiphilic star-shaped brushes based on block copolymers-molecular micelles for the delivery of drugs: Hydrodynamic studies

Brush-shaped molecular stars of poly(ɛ-caprolactone)-block-poly(oligo(ethylene glycol) methacrylate) are synthesized, their hydrodynamic properties are studied, and their molecular characteristics are measured. For dilute solutions of the copolymers in acetone, viscous flow, velocity sedimentation, and translational diffusion of the macromolecules are investigated. The molecular masses of the copolymers are determined via the Svedberg relation. Correlations between hydrodynamic characteristics and molecular masses in the range 46 < M × 10−3 g mol−1 < 266 are obtained. The existence of scaling relationships makes it possible to infer that the resulting copolymers belong to a hydro-dynamically similar series of macromolecules: hydrodynamic homologs. It is shown that copolymer macromolecules have a denser organization in space than that of both linear macromolecules and conventional molecular stars. A model of macromolecules of poly(ɛ-caprolactone)-block-poly(oligo(ethylene glycol) methacrylate) copolymers that is based on their hydrodynamic characteristics is discussed.

Conformational and hydrodynamic properties of the homopolymer of 2-deoxy-2-methacrylamido-D-glucose and its copolymers with acrylic acid and methacrylic acid

Hydrodynamic properties of the homologous series of the homopolymer 2-deoxy-2-methacryla-mido-D-glucose and the copolymers of 2-deoxy-2-methacrylamido-D-glucose with unsaturated acids in 0.2 M NaCl are studied via static and dynamic light scattering, viscometry, refractometry, and translational diffusion. The copolymers synthesized via the free-radical copolymerization of 2-deoxy-2-methacrylamido-D-glucose with acrylic acid or methacrylic acid contain ∼20 mol % acid units. At this amount of acid units, the equilibrium rigidity of copolymer chains corresponds to that of homopolymer chains. The copolymers are distinguished by the hydrodynamic characteristics of molecules. The copolymer with methacrylic acid is similar to the homopolymer, whereas the copolymer with acrylic acid features substantially different parameters of relationships relating the hydrodynamic characteristics of homologs to their molecular masses.

The electro-optic properties of fluorinated polydialkoxyphosphazenes with different lengths of side substituents

Polydialkoxyphosphazenes with partially fluorinated side substituents of different lengths in dioxane and ethyl acetate are studied via the methods of the equilibrium electro-optic Kerr effect, isothermal translational diffusion, and viscosimetry. It is experimentally found that the magnitude and sign of the Kerr constant depend on the length of the side substituents. The observed dependence is explained by the changes in the optical polarizability tensor and the angle between the direction of the permanent dipole moment and the primary axis of optical polarizability of the monomer unit of these macromolecules with an increase in the number of carbon atoms in the chains of alkoxy substituents attached to phosphorus. It is shown that fluorinated polydialkoxyphosphazenes are comblike polymers with high equilibrium skeletal rigidity and non-coincident principal directions of the optical polarizability and dielectric polarizability of the monomer unit.

Formation of interpolyelectrolyte complexes with controlled hydrodynamic radii in solutions

Interpolyelectrolyte complexes (IPEC) of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and comb-like amphiphilic polyelectrolyte poly(11-acryloyloxyundecyltrimethyl-ammonium) cation (PAUTA) were synthesized via polymerization of AUTA ionically bound to a PAMPS macromolecule. Nanoparticle dispersions with controlled hydrodynamic radii were prepared by varying molecular weight of the initial PAMPS. The morphology and sizes of IPEC dispersions were studied by atomic force microscopy (AFM). Nanoparticles dispersions stability under different salt conditions was assessed.