M. E. Mikhailova

Molecular properties of conjugates formed by synthetic hydrophilic polymers and sterically hindered phenols

Water-soluble conjugates are prepared via the chemical modification of poly(vinyl alcohol) and poly(ethylene glycol) by antioxidants taken from the family of sterically hindered phenols. The effects of the degree of substitution of conjugates on the dimensions of molecules and their aggregates are studied by viscometry and light scattering in dilute solutions. It is shown that an increase in the amount of antioxidant groups incorporated into the poly(vinyl alcohol) chain leads to a decrease in the dimensions of single conjugate molecules owing to attraction of hydrophobic groups. Poly(ethylene glycol) molecules carrying end groups of sterically hindered phenols form micellar aggregates that are absent in the solution of the initial polymer. The mean number of molecules involved in such an aggregate is 83. It is found that the presence of hydrophobic end groups in poly(ethylene glycol) molecules causes a sharp reduction in the lower critical solution temperature of a solution relative to that of the initial polymer.

Conformational, optical, electro-optical, and dynamic characteristics of cross-linked poly(N-acryloyl-11-aminoundecanoic acid)

Polymerizable surfactants now attract a great interest due to high potential of their practical application as components of pseudostationary phase in micellar chromatography, drug carriers, and “building blocks” for molecular design of nanoparticles and nanostructured polymer materials, for encapsulation of various biological preparations. In the present work, we have studied poly(N-acryloyl-11-aminoundecanoic acid) (cross-linked comb-like polymer). Cross-linked polymers were obtained via copolymerization of the surfactant bearing double bond in hydrophobic tail with hydrophobic bifunctional cross-linker in micellar solution. Of special interest was the comparison between cross-linked and non-cross-linked polymers and influence of alkaline medium on characteristics of these samples. Non-cross-linked polymers were obtained by hydrolysis of the cross-linked product (treating with NaOH). The mixture of cyclohexanol and dioxane (1:1 volume ratio) was used as a solvent. Detailed studies of the obtained polymers by viscometry, dynamic light scattering, flow birefringence, and equilibrium and non-equilibrium electric birefringence were performed. It was established that during cross-linking process, two types of bonds are formed (the ones inside individual molecules and between several polymer chains). It was shown that cross-linked macromolecular nanoparticles can be transformed into comb-like polymers.

Molecular characteristics and antioxidant activity of polyethylene glycols modified by sterically hindered phenols

Chemical modification of polyethylene glycols by antioxidants belonging to the class of sterically hindered phenols is used to obtain water-soluble conjugates differing in the structure of the joined antioxidant and molecular weight. The inclusion of hydrophobic end groups in polyethylene glycol molecules leads to a decrease in the lower critical mixing point of the solution as compared to the original polymer. Dilute solution viscometry and light scattering are used to determine the molecular-mass characteristics of the polymers and the hydrodynamic radii of single conjugate molecules. The mass fraction of single molecules in aqueous solutions of the conjugates is greater than 95%. The aggregates are micellar-type particles whose core is formed by the hydrophobic moieties of sterically hindered phenols. It is shown that the antiradical activity of the antioxidants 3-(3-tert-butyl-4-hydroxy-5-methylphenyl)-propionic acid and 3- (3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid, which are used for the modification, differs only slightly, whereas the activity of the relevant conjugates increases significantly.

Hydrodynamic and conformational properties of dendron-modified polystyrene molecules

The molecular characteristics of polystyrene modified by the Frechet type dendrons of 1–4 generations were studied in tetrahydrofuran by viscometry, isothermal diffusion, electric birefringence, and dynamic and static light scattering. It was shown that dendronized polystyrene molecules whose polymerization degree changes from 1640 to 930 with an increase in the generation number of dendrons occur in the coillike conformation. The equilibrium rigidity of macromolecules tends to increase with increasing the generation number of dendrons. The Kuhn segment length grows from 3.9 nm for polystyrene molecules modified by dendrons of the first generation to 23.3 nm for polystyrene molecules carrying dendrons of the fourth generation.

Electrical and dynamooptical properties of Frechet dendron-modified polystyrene molecules in solutions

The electrooptical, dynamic, and dielectric characteristics of polystyrene modified by the Frechet dendrons of 1–4 generations have been studied in benzene, chloroform, and THF solutions. It has been shown that the Kerr constant and the shear optical coefficient for all the studied polymers coincide in sign and their absolute values increase with the dendron generation number. The intrinsic optical anisotropy of the repeating unit of dendronized polystyrene molecules is negative in sign, and its absolute value tends to grow with an increase in the generation number of dendrons. The frequency dispersions of the Kerr constand and of the dielectric polarization have been discovered for solutions of the modified polymer. The ratio between the times of relaxation characterizing the dispersion of dielectric permittivity and of the Kerr constant of solutions and the times of a rise and decay of electric birefringence measured on the onset and termination of the rectangular-pulsed field does not obey the longitudinal relaxation theory for polar macromolecules. The relaxation times of dielectric polarization and of electric birefringence tend to increase with the dendron generation number.

Electroptical and dynamic properties of sulfonated polystyrene molecules and their associates in chloroform

The behavior of sulfonated PS containing 0.5, 1.35, 2.6, and 5.8 mol % of sodium sulfonate groups in chloroform solutions has been studied by static and dynamic light scattering, viscometry, and electric birefringence. The molecular mass of ionomers is measured, and their translational diffusion coefficient, intrinsic viscosity, and free relaxation times are estimated. It has been shown that association in solutions of ionomers containing more than 1.35 mol % of sodium sulfonate groups proceeds according to the open association model. Analysis of autocorrelation functions of scattered light intensity and electric birefringence decay makes it possible to determine translational diffusion coefficients and relaxation times for individual ionomer molecules, their pair associates, and higher multiplicity associates. With an increase in the fraction of sodium sulfonate groups, the hydrodynamic radius of individual ionomer molecules decreases from 8 to 5.8 nm, while the ratio between the hydrodynamic radius of pair associates and individual sulfonated PS molecules increases.

Molecular and conformational properties of comb-like polymers with ionically bound side chains studied in organic solvent

ABSTRACT Conformational and dynamo-optical properties of a homologous series of poly(cetyltrimethylammonium 2-acrylamido-2-methylpropane sulfonates) with molecular masses ranging from 80 to 700 kDa were studied in chloroform solutions by viscometry, dynamic light scattering, sedimentation, and flow birefringence. The Mark–Kuhn–Houwink Equations for this polymer in chloroform were obtained; the values of hydrodynamic diameter and the Kuhn segment length as well as the value of intrinsic anisotropy of polarizability of the monomer unit were defined.

Molecular and Conformational Properties of Dendronized Polymethacrylate in Organic Solvent

The conformational and dynamo-optical properties of a homologous series of polymethacrylate modified by first-generation Fréchet-type dendrons in the molecular mass range of 70–8800 kDa in organic solvents were studied by viscometry, isothermal diffusion, dynamic light scattering, and flow birefringence. The Mark-Kuhn-Houwink equations for this dendronized polymer in toluene and chloroform together with hydrodynamic diameter and Kuhn segment length in toluene are defined as well as the value of intrinsic anisotropy of polarizability for the monomer unit.

Indicator properties of oligoethylene glycol hybrids with sterically hindered phenols

Aqueous solutions of hybrid compounds (conjugates) formed by polyethylene glycols modified at the terminal hydroxy groups with sterically hindered phenol lose their phase stability at a certain temperature which depends on the molecular weight of polyethylene glycol, structure of sterically hindered phenol, conjugate concentration, and composition of the medium. This property may be used to estimate the effect of structural factors on the hydrophobic-hydrophilic balance in the conjugate-water system.