Alina I. Amirova

Thermoresponsive Star-Shaped Poly(2-isopropyl-2-oxazoline) in Aqueous Solution

Thermoresponsive star-shaped poly(2-isopropyl-2-oxazoline) with t-butylcalix[8]arene core was studied by light scattering methods in aqueous solution. The sample under investigation has Mw = 19600 g mol−1 and PDI of arms 1.41. The bimodal distribution of scattering objects was observed even at room temperature. The redistribution of these two kinds of particles takes place at T = 27°–36°C. At higher temperatures the growth of large particles, disappearance of the small component, and appearance-disappearance of “middle-size” aggregates were observed. Only the large particles with the hydrodynamic radius 95 nm exist in proximity to LCST (37.5°C).

Influence of arm length and number on star-shaped poly(2-isopropyl-2-oxazoline) aggregation in aqueous solutions near cloud point

Four-arm star-shaped poly(2-isopropyl-2-oxazolines) (PiPrOx4) are synthesized by cationic polymerization on t-butylcalix[4]arene macroinitiator. The obtained samples differ by polymerization degree of arms NPiPrOx = 9 and 25 and are characterized in chloroform. The behavior in aqueous solutions is studied by light scattering methods and compared with the results of investigation of eight-arm star with similar structure. Three types of particles are observed in solution of short-arm PiPrOx4 at room temperature, whereas only two particle types are present in long-arm star solution. Arm shortening leads to widening of the phase transition interval. The arm number decreasing reduces the phase transition temperature by 1°C.

Deuterium Isotope Effect on Solution Behavior of Thermoresponsive Star-Shaped Poly(2-isopropyl-2-oxazoline)

Thermosensitive star-shaped poly(2-isopropyl-2-oxazoline) (molar mass M≈21000 g mol−1) in D2O solution was studied by the static and dynamic light scattering methods. The behavior of the polymer investigated in deuterated water is similar qualitatively to that observed previously in undeuterated water. At the same time, the considerable quantitative changes of polymer behavior in D2O were seen. Deuterium substitution of solvent affects the phase transition temperature by decreasing its value by 1°C. The temperature interval of phase transition in D2O solution expands (by about 1°C) in comparison with that in H2O solution.

Behavior of hyperbranched polymers in solutions

Hyperbranched polycarbosilanes are investigated by the methods of molecular hydrodynamics and optics. Dependences of the hydrodynamic and conformational properties of these polymers on their molecular mass, the length of linear chains between branching points, and the chemical structure of end groups are analyzed. The hydrodynamic behavior of hyperbranched polycarbosilanes is explained by the fact that the dimensions of their macromolecules are compact and their shape is close to spherical. The convolution of chains between branching points becomes more pronounced with an increase in their length and a decrease in the molecular mass of the polymer. When end fluorinated groups are incorporated into the hyperbranched polycarbosilane, in thermodynamically good solvents and θ solvents, hydrodynamic characteristics change apparently owing to a change in the density of macromolecules in solution. In a poor solvent, the compaction of fluorinated macromolecules and a reduction in their shape asymmetry are observed. At a fixed branching degree, the hydrodynamic properties of hyperbranched polymers depend on the structural regularity of their macromolecules: In terms of hydrodynamic properties, the hyperbranched polycarbosilane with a degree of branching of 1 and a random distribution of branching points within the volume of a macro-molecule is appreciably different from a dendrimer of the same chemical nature and is close to polycarbosilanes with a degree of branching of 0.5.

Time dependence of the aggregation of star-shaped poly(2-isopropyl-2-oxazolines) in aqueous solutions

The paper concerns the analysis of time teq required to equilibrium state achievement in aqueous solutions of star-shaped poly(2-isopropyl-2-oxazolines) (PiPrOx) after changing temperature. The discussed data were obtained for PiPrOx differing in arm number and length. For all samples, high teq values, half an hour at least, were obtained because of rather high intramolecular density. The dependence teq on temperature displayed maximum near the phase separation beginning due to the aggregate growth and redistribution of scattering particles. The maximum times teq increased symbatically with arm number and length. The higher energy of the hydrogen bond formed by deuterium isotope leads to the growth of the teq values as compared to solutions in H2O.

Establishment of Equilibrium in Solutions of Thermoresponsive Polyoxazoline After Discrete Temperature Changes

Establishment of equilibrium after temperature changes of aqueous solutions of star-shaped eightarm poly(2-isopropyl-2-oxazoline) with calix[8]arene in the core was studied using light scattering. The times to establish equilibrium teq in the solution were determined as functions of temperature and concentration. It was found that teq increased several times (up to 10) compared with teq at low temperatures as the turbidity temperature was approached. It was shown that teq increased with increasing solution concentration.

Role of the deuterium isotope in the formation of the behavior of thermosensitive poly(2-isopropyl-2-oxazoline)

Thermosensitive star-shaped poly(2-isopropyl-2-oxazoline) is studied via light scattering in D2O solutions in a ten-fold concentration range at the temperatures from 21 to 60°С. The data are compared to the results of investigations on this polymer in Н2O at close concentration values. A qualitative similarity in behavior of the polymer in the compared solvents is established; the changes that occur after the change from Н2O to D2O are quantitative. After changing to the deuterated solvent, the initial temperature of phase separation decreases by 0.5–1.0°С. The lower the solution concentration, the greater the width of the phase-separation interval.

Temperature Dependence of the Hydrodynamic and Conformational Properties of Hyperbranched Polycarbosilanes

Three types of carbosilane hyperbranched polymers were studied in dilute solution in toluene. The samples had different lengths of chains between branch points and the structure of terminal groups (butyl, undecenyl, or fluorine containing). The temperature dependences of intrinsic viscosity and second virial coefficient values were determined by viscometry and static light scattering methods. It is shown that conformational characteristics of hyperbranched polycarbosilanes do not depend on the thermodynamic quality of a solution in the wide range of temperatures.

Solution properties of new “core-shell” structured polyorganosilsesquioxanes with two different types of “core-shell” surroundings

ABSTRACT Two “core-shell” structured polyorganosilsesquioxanes, differing in the arrangement of vinyl groups over the macromolecule volume, were studied in dilute solutions in toluene and ethyl acetate. It is shown that solution behavior is determined by the transposition of the functional vinyl groups in the core or shell of the macromolecule. This correlation is manifested in increasing the intrinsic viscosity values.

Solution Behavior of Hyperbranched Polymethylsilsesquioxane with Intramolecular Cycles

Samples of hyperbranched polymethylsilsesquioxanes were synthesized at various polycondensation times and intramolecular cycle amounts. The samples were studied in solutions in toluene and hexane. It is shown that increasing the polycondensation duration results in the growth of number of cycles and intramolecular density that correlates with changes of molecular, hydrodynamic, and optic properties.