Synthesis and self-organization studies of polyionic complexes of linear–dendritic copolymers based on polyethylene glycols bearing aspartic dendrons with terminal amino and carboxylic groups.

Reducing and stabilizing abilities of three poly(ethylene glycol) (PEG) samples modified with primary amino groups in one or two terminal positions of the polymer chains, as well as with dendrons based on L-aspartic acid in both terminal positions of the polymer chains, have been studied. Stable dispersions of silver nanoparticles have been formed at room temperature in aqueous solutions of AgNO3 in the presence of the modified PEGs without additional reducing agents. Spectrophotometric examinations have shown that an increase in the number of amino groups per polymer molecule results in accelerating the formation of nanoparticles and improving the stabilizing ability of the modified PEGs. Molecular hydrodynamic methods (analytical centrifugation and dynamic light scattering) have been used to determine the absolute values of the molecular mass of silver nanoparticles stabilized with dendronized PEGs and the hydrodynamic sizes of the particles. Molecular hydrodynamics and electron microscopy have yielded interconsistent estimates of silver nanoparticle sizes.

Three polymerizable surfactants (surfmers) bearing 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as polymerizable group in the counterion have been designed, synthesized, and their micelle-forming properties have been investigated in different solvents. Solutions of dodecylammonium (DDA-AMPS), cetylammonium (CA-AMPS), and cetyltrimethylammonium (CTA-AMPS) 2-acrylamido-2-methylpropanesulfonates were studied in water, water-dioxane mixtures in a whole range of components ratios, and xylene. The solutions were investigated by capillary and rotational viscometry, conductometry, and small-angle neutron scattering; aggregates adsorbed from the solutions on as-split mica were studied by atomic force microscopy (AFM). The surfmers follow general regularities of surfactant behavior in aqueous solutions. Decrease in polarity of the media with an increase in dioxane content in water-dioxane mixtures leads to disappearance of direct micelles. At low water content (below 5%) the surfmers form reverse micelles in the mixtures. The surfmers form reverse micelles in low polarity solvents, such as xylene, which should affect the polymerization results.

Various acrylic polymers in which an aspartic acid fragment with different end groups (the firstgeneration dendron) is attached to the main chain either via the amide group or the 4-aminobenzoic acid residue are studied. The synthesis of monomers and polymers with the asymmetric substitution of the aspartic fragment, in which a long hexadecyl group is situated only at the α-carboxyl group, is described. The molecular, optical, electrooptical, and conformational properties of the polymer containing the long hexadecyl group at the α-carboxyl bond and the hydrolyzed β-ester bond in the aspartic acid fragment are examined in detail. In the range M = (23−508) × 103, the Mark-Kuhn-Houwink equations [η] ∼ M 0.53 and D ∼ M −0.53 are obtained for the intrinsic viscosity and diffusion of the polymers under study in octyl alcohol. The length of the statistical Kuhn segment (120 Å), the hydrodynamic diameter of a chain (50 Å), the shear optical coefficient, and the anisotropies of the segment and monomer unit are determined. An analysis of the experimental data shows that the main optical axis of the side hexadecyl chain makes an angle of ∼54.5° with the direction of the main chain.

The molecular characteristics of cylindrical first-third generation dendrimers carrying dendrons based on L -aspartic acid are compared. It is shown that both the generation number of side dendrons and their structure determine the conformational, hydrodynamic, optical, and dipole characteristics of dendrite macromolecules. It is found that the studied class of cylindrical dendrimers is distinguished by a marked amount of intramolecular hydrogen bonds between side dendrite substituents. These bonds ensure the unusual combination of high kinetic rigidity and a compact conformation (low equilibrium rigidity) of macromolecules. The rupture of hydrogen bonds leads to an enlargement of molecular coils (an increase in equilibrium rigidity) that is accompanied by a sharp drop in kinetic rigidity.

Исследованы различные структуры акриловых полимеров, в которых фрагмент аспарагиновой кислоты с различными концевыми группами (дендрон первой генерации) присоединен к основной цепи либо через амидную группу, либо через остаток 4-аминобензойной кислоты. Описан синтез мономеров и полимеров с несимметричным замещением аспарагинового фрагмента, который только по -карбоксильной группе имеет длинную гексадецильную группу. Наиболее детально исследованы молекулярные, оптические, электрооптические и конформационные свойства полимера с длинной гексадецильной группой по -карбоксильной связи и гидролизованной -сложноэфирной связью во фрагменте аспарагиновой кислоты. В интервале М = (23–508) ? 103 для характеристической вязкости и диффузии в октиловом спирте получены уравнения Марка–Куна–Хаувинка: [ ] М 0.53 и D M-0.53. Определены длина статистического сегмента Куна (120 A), гидродинамический диаметр цепи (50 A), оптический коэффициент сдвига, анизотропии сегмента и мономерного звена. Анализ экспериментальных данных показал, что главная оптическая ось боковой гексадецильной цепочки составляет угол 54.5° относительно направления основной цепи.

Выполнен сравнительный анализ результатов систематических исследований молекулярных характеристик цилиндрических дендримеров первой–третьей генераций с дендронами на основе L-аспарагиновой кислоты. Показано, что как номер генерации боковых дендронов, так и их структура определяют конформационные, гидродинамические, оптические и дипольные характеристики дендритных макромолекул. Установлено, что специфической особенностью исследованного класса цилиндрических дендримеров является значительное количество внутримолекулярных водородных связей между боковыми дендритными заместителями. Эти связи обеспечивают необычное сочетание высокой кинетической жесткости и компактной конформации (низкая равновесная жесткость) макромолекул. Разрыв водородных связей приводит к увеличению размеров молекулярных клубков (рост равновесной жесткости), сопровождающемуся резким падением кинетической жесткости.

Acrylic polymers containing side dendrons of the third generation based on L -aspartic acid have been studied via the methods of molecular hydrodynamics, dynamic and static light-scattering, optics, and electrooptics. There are marked differences in hydrodynamic and optical properties of the macromolecules under study and previously examined polymers with side dendrons of first and second generations. In the range of degrees of polymerization from 10 to 40, these macromolecules possess an extremely low shape asymmetry. Experiments demonstrate the predominant orientation of end side dendrons along the main molecular chain. In chloroform solutions, the orientation of macromolecules in hydrodynamic and electric fields occurs according to the large-scale mechanism. In dichloroacetic acid, the hydrodynamic dimensions of macromolecules decrease, an effect that is accompanied by an increase in the kinetic flexibility of polymer chains.

Original method for synthesis of N-carboxyanhydrides of trifunctional α-amino acids containing substituents attached by amide bonds at the ω-functional group is suggested.

Linear polymers with dendrons of first and second generations based on L-aspargic acid are studied by the methods of flow birefringence and electric birefringence. Optical, dipole, dynamic, and conformational properties of the macromolecules, as well as contributions to their optical anisotropy due to macroform and microform effects, are investigated. The polymers are found to possess permanent electric dipole moments and undergo reorientation in external electric and hydrodynamic fields according to large-scale rotation mechanism. A significant growth in equilibrium rigidity, optical anisotropy, and dipole moment of monomer units is observed when rigid benzamide fragments are introduced into the dendrimers. The backbone conformation of second-generation dendrimers containing such fragments is shown to be well described by generalized wormlike chain model.

The linear dendritic polymers of the first and second generations have been investigated by the methods of flow birefringence and equilibrium and nonequilibrium electric birefringence. The side dendrons are attached to the polymer backbone through benzamide groups and contain long terminal hexyloxycarbonyl fragments. Optical, dynamic, dipolar, and conformational characteristics of the macromolecules in question have been analyzed in detail. It has been found that the macromolecules of dendritic polymers with dendrons based on L-aspartic acid possess permanent dipole moments and reorient in external electric and hydrodynamic fields according to the large-scale rotation mechanism. The introduction of rigid benzamide fragments substantially increases the equilibrium rigidity, optical anisotropy, and dipole moment of monomer units of dendritic macromolecules. The role of macro-and microform effects in the formation of optical features of the molecules under study is considered in detail.

The conformational properties of poly(acrylate) with L-aspartic acid-based side dendrons of the first and second generations with hexyloxycarbonyl end groups have been studied by the methods of molecular hydrodynamics. Regularly branched dendrons are separated from the main chain by a benzamide fragment. The degree of polymerization of the main chain varies within 30-and 50-fold intervals for the dendrons of first and second generations, respectively. Mark-Kuhn-Houwink equations have been derived for poly(acrylate) in bromoform and dichloroacetic acid containing lithium chloride additives. The experimental results are discussed in terms of the models of the wormlike chain, weakly bent cylinder, and solid ellipsoid of revolution. On the basis of translational and rotational friction data, the persistent length of poly(acrylate) in bromoform and dichloroacetic acid containing small amounts of lithium chloride has been estimated.

Методами молекулярной гидродинамики изучены конформационные свойства полиакрилата с боковыми дендронами первой и второй генераций на основе L-аспарагиновой кислоты с гексилоксикарбонильными концевыми группами. Регулярно разветвленные дендроны отделены от основной цепи бензамидным фрагментом. Значения степени полимеризации основной цепи изменялись в тридцати- и пятидесятикратном интервале для первой и второй генераций дендронов соответственно. Получены уравнения Марка–Куна–Хаувинка для полиакрилата в бромоформе и дихлоруксусной кислоте с хлористым литием. Обсуждение экспериментальных результатов выполнено в рамках моделей червеобразной цепи, слабоизогнутого цилиндра и сплошного эллипсоида вращения. На основании данных по поступательному и вращательному трению оценена персистентная длина полиакрилата в бромоформе и дихлоруксусной кислоте с хлористым литием.

Two series of new acrylic polymers carrying L -aspartic acid-based dendrons in side chains with terminal hexyloxycarbonyl groups that are both directly and indirectly, via a rigid spacer, attached to polymer chains have been synthesized by the free-radical polymerization of monomers. The polymerization ability of the monomers has been studied. The properties of new polymers are compared with the properties of polymer analogs containing terminal methoxycarbonyl groups of dendrons. Upon incorporation of the rigid spacer, the shielding of reactive centers decreases and the polymerizability of the monomers increases. The replacement of terminal methyl groups in dendrons with hexyl groups in spacer-free polymers leads to a reduction in the degree of polymerization, while in the case of polymers containing spacers, high-molecular-mass products arise. This phenomenon is facilitated by the amphiphilic nature of the polymers and the additional enhancement in the rigidity of chains. A polymer carrying a third-generation dendron has been synthesized only for the latter series.

The oligomers of a poly-7-glutamic acid with dendrons in side chain on the basis of L-aspartic acid axe obtained by polycondensation of dendronized dimers. The hydrolysis of terminal methoxycarbonyl groups of polymers with the first generation dendrons is accomplished and water soluble anionic polyelectrolyte is obtained. It is determined that such polymers take coil conformation independently of medium's pH.

Cylindrical dendrimers of first, second, and third generations with side dendrons based on L-aspartic acid which are attached to poly(styrenesulfonic acid) chains via ionic bonds are studied by molecular hydrodynamic, optical, and electrooptical measurements. Macromolecules of the said dendrimers demonstrate significant kinetic rigidity in external electric and hydrodynamic fields simultaneously with moderate equilibrium chain rigidity. The comparative analysis of the experimental data on various cylindrical dendrimers with the polyvinyl backbone and L-aspartic acid-based dendrons is performed. It has been shown that, in solvents not disturbing intramolecular hydrogen bonds between side dendrons, the conformational and dynamic properties of various cylindrical dendrimers are similar. The molecular characteristics of cylindrical dendrimers in non-dissociating solvents are insignificantly affected by the mode of dendron attachment to the backbone (covalent or ionic binding).

The conformation and physical properties in dilute solutions of macromolecules of L-aspartic acid-based cylindrical dendrimers of the second generation were studied by the methods of molecular hydrodynamics, optics, and electrooptics. Dichloroacetic acid and dichloroacetic acid containing LiCl additives were used as solvents. It was shown that the rupture of the system of intramolecular hydrogen bonds in dendrimers leads to an increase in the unperturbed dimensions of polymer coils (a rise in the equilibrium rigidity of the main chain) with a concomitant sharp drop in the kinetic rigidity of macromolecules. These unusual changes are related to the chemical structure of the cylindrical dendrimers under study which contain a great number of amide groups in side dendrons. The role of volume effects in the formation of conformational properties of polymer chains of cylindrical dendrimers in solutions was examined in detail. The comparative analysis of the experimental data obtained for cylindrical dendrimers in solutions of dichloroacetic acid and dioxane was performed.

Specimens of linear polymers with attached L-aspartic acid-based first-, second-, and third-generation conical dendrons as side groups, in which regularly branched dendrons were separated from the main chain by a benzamide spacer, were synthesized. The linear dendrimers were studied using the techniques of flow birefringence, viscometry, equilibrium and nonequilibrium electric birefringence, and dynamic light scattering. The optical, dynamic, and conformational characteristics of macromolecules of these polymers were determined. It was shown that the introduction of the benzamide spacer between the acrylic main chain and the dendrons leads to a dramatic change in the optical and electrooptical characteristics of dendronized linear polymers. The specific role of intramolecular hydrogen bonding in the formation of conformational and dynamic properties of macromolecules of cylindrical dendrimers based on L-aspartic acid was thoroughly studied and analyzed.