Andrey V. Tenkovtsev

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).

The Use of Structure Analysis Methods in Combination with Semi-empirical Quantum-Chemical Calculations for the Estimation of Quadratic Nonlinear Optical Coefficients of Organic Crystals

An effective search for new organic crystals for prospective use in nonlinear optical (NLO) applications requires quantitative and fast experimental determination of their NLO properties at a molecular level. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time-consuming and sometimes impossible task. Single crystals of a considerably smaller size may be effectively used for complete structural analysis by electron diffraction combined with simulation methods. When the crystal structure of a given compound is known, its NLO properties may be estimated using quantum-chemical methods for calculation of the molecular nonlinearity tensor and the relationships between its components and the macroscopic coefficients of the crystalline nonlinearity tensor. In the present work, the semiempirical PM-3 method was employed for this aim.

Synthesis of high-molecular weight liquid crystal polyesters based on a polycondensation mesogenic monomer☆

Abstract This paper relates to the scheme proposed for the synthesis of high-molecular weight alkylene aromatic polyesters capable of forming liquid-crystal melts. This is the first time that the mesogenic dichloride, terephthaloyl-bis-(4-oxybenzoyl chloride) has been separated and characterized. Polycondensation of this diacidchloride with various aliphatic and hydroxyaliphatic diols resulted in polymers with temperatures of transition to the liquid-crystal state in the interval from 40 to 360°. The procedure and conditions of polycondensation were selected, taking as an example the synthesis of a single polymer, polydecamethyleneterephthaloyl-bis-(4-oxybenzoate). Relations between phase transition temperatures and MW have been investigated for this polymer.

Strategies for structure solution and refinement of small organic molecules from electron diffraction data and limitations of the simulation approach

In recent years, a series of non-linear optically active bis(benzylidene) ketones have been synthesized and investigated by electron crystallography. In most cases, structure refinement was possible by combining electron diffraction analysis and quantum-mechanical calculations with maximum-entropy methods. However, when the torsional angles between the phenyl rings and the C=C double bonds are strongly affected by the crystal field, this method fails because packing-energy calculations are not sufficiently sensitive. This problem can be solved by refining the approximate model with SHELXL, if the data set is sufficiently accurate and the model close to the correct structure. Here it is shown that a considerably superior data set can be obtained at 300 kV with on-line data acquisition.

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.

Comparison of electron diffraction data from non-linear optically active organic DMABC crystals obtained at 100 and 300 kV

During the recent past, we have synthesized a new class of molecules with intramolecular two-dimensional charge transfer upon excitation. The present report presents such a molecule, 2,6-bis(4-dimethylamino-benzylidene)-cyclohexanone (DMABC), with an unusually high value of the second-order non-linear optical (NLO) coefficients. In order to optimize the macroscopic NLO properties of the compounds, it is necessary to relate their first hyperpolarizability tensors at a molecular level to those at a crystal bulk level. This requires a complete structure determination and refinement. However, the growth of sufficiently large single crystals, which are needed for structural analysis and refinement by X-ray methods, is a time consuming and sometimes impossible task. We have performed a complete structural analysis by electron diffraction combined with simulation methods and with maximum entropy and log likelihood statistics. In order to improve the quantitative analysis, a 300 kV data set using an on-line CCD camera was added and the best attainable R-values were compared with those from 100 kV data using film emulsions. Details regarding the maximum attainable resolution for both data sets are discussed as well as the problems which arise from the limited dynamic range in photographic emulsions as compared to a 14 bit CCD camera. Once the crystal structure was known, quantum-chemical methods were used to calculate non-linear optical susceptibility tensor components and these were related to the macroscopic coefficients of the crystalline quadratic non-linearity tensor. In the present work, both ab initio and semi-empirical quantum-chemical calculations were employed.

Studies of structures and properties of polymeric systems containing bis-(hydroxy-arylidene)alkanones as NLO-active chromophores

Abstract NLO-properties of polymer systems containing bis-(hydroxy-arylidene)alkanone chromophores were studied experimentally and analyzed using ab initio quantum chemical calculations. A monoclinic crystal structure (space group P2111) of the polyester containing fragments of such chromophores in the backbone was simulated and a reasonable agreement between the experimental and simulated X-ray powder diffraction patterns was achieved. Ab initio quantum-mechanical estimations of the SHG-observable macroscopic second-order non-linearity tensor coefficients, obtained for the polymer crystal structure at the HF SCF level, led to the major dXZZ-coefficient of 1.9 pm/V. Films of ionic complexes of strongly basic poly-1,10-decamethylene-acetamidine with various bis-(hydroxy-arylidene)alkanone chromophores were prepared and shown to display considerable THG-efficiencies. The molecular structure of these complexes is discussed on the basis of the experimental spectroscopic data and calculated relative stabilities of different forms of the complexes. The formation of the complexes results in a considerable increase of the glass transition temperature by ≈70°C.

Behavior of thermosensitive graft copolymer with aromatic polyester backbone and poly-2-ethyl-2-oxazoline side chains in aqueous solutions

ABSTRACT Thermoresponsive graft copolymers with alkylene-aromatic polyester main chain and poly-2-ethyl-2-oxazoline side chains were synthesized. Two copolymer samples which differed in grafting density (0.5 and 0.7) were studied using dynamic and static light scattering and turbidimetry in aqueous solutions at concentration 0.0053 g cm−3. Hydrodynamic radii of scattering objects and their contribution to light scattering were obtained as a function of temperature in a wide temperature interval. Temperatures of phase separation were found out. Effect of grafting density on the copolymer behavior in aqueous solutions upon heating was determined. In particular, the phase separation temperature reduces with the decreasing grafting density.

Behavior of aqueous solutions of polymer star with block copolymer poly(2-ethyl-2-oxazoline) and poly(2-isopropyl-2-oxazoline) arms

ABSTRACT Eight-arm star-shaped poly(2-alkyl-2-oxazoline) (M ≈ 21,000 g · mol−1) was studied by turbidimetry and light scattering in aqueous solutions within concentration ranging from 0.00038 to 0.0276 g · cm−3. The arms were the block copolymers of poly(2-isopropyl-2-oxazoline) (PiPrOx) and poly(2-ethyl-2-oxazoline) (PEtOx). Calix[8]arene core was connected with poly(2-isopropyl-2-oxazoline). The behavior of investigated polymer differed from that of thermosensitive stars with poly(2-alkyl-2-oxazoline) homopolymer arms. At low temperatures, the aggregates were formed due to interaction of hydrophobic cores. The phase separation temperatures T1 and T2 of studied star were higher than those for star-shaped poly(2-isopropyl-2-oxazoline) and lower than for poly(2-ethyl-2-oxazoline). T1 and T2 increased with dilution.

Hydrodynamic, optical and conformational properties of molecules of aromatic polyesters containing 3,3′-biphenylene fragments in the main chains

Abstract The hydrodynamic, optical and conformational properties of molecules of fractions of two aromatic polyesters (APE) containing 3,3′-biphenylene fragments in their chains have been investigated by sedimentation-diffusion analysis and flow birefringence in dilute solutions. The experimental data on the translational mobility and dynamo-optical characteristics of molecules of these polymers are compared with those for previously investigated APE with similar structures but containing no biphenylene fragments. As a result of this analysis, the geometric parameters of the repeating chain unit were characterized, and the equilibrium rigidities of the molecule of the APE were estimated. It was shown that the flexibility of these molecules is determined by the character of intramolecular rotation about the biphenylene bond and that this rotation is virtually unhindered.