Scientific results:
As part of the implementation of the project we used controlled atom transfer radical polymerization (ATRP) on a multicenter polyimide macroinitiator to synthesize macromolecular brushes with a polyarylene backbone and side chains consisting of poly(methyl methacrylate) (PMMA), poly(tert-butyl methacrylate) (PtBMA), poly(N,N-dimethylamino-2-ethyl methacrylate) (PDMAEMA) and poly (n-butyl acrylate) (PnBA). A methodology has been developed for the analysis of the molecular-mass characteristics of the synthesized macromolecular brushes that relies on the use of the method of exclusion liquid chromatography (ELC) with the use of a refractometric and a viscosimetric detector as well as a light scattering detector (so-called «triple detection»). This technique allows to reliably determine the molecular-mass characteristics of both macromolecular brushes themselves and their constituent parts (the backbone and the side chains). The data gathered in the process correspond to data collected by absolute methods (sedimentation-diffusion analysis).
Our researchers have synthesized multicenter oligoester microinitiators with 2-(bromoethyl)phenyl groups in a monomer unit that are able to initiate the polymerization of 2-alkyl-2-oxazolines. Using these macroinitiators with the help of controlled ring-opening polymerization of 2-alkyl-2-oxazolines, we have produced macromolecular brushes with an oligoester backbone and oxazoline side chains. We have proven that the polymerization of 2-alkyl-2-oxazolines on multicenter oligoester macroiniticators proceeds in the «live chains» mode (without irreversible breakage), but is characterized by a slower initiation. It has been demonstrated that the average length of grafted oligooxazoline chains amounts to 26-29 monomer units at an initial initiator/monomer ratio of 1/30, 50-54 – at a ratio of 1/60 and 90-95 – at a ratio of 1/100. The grafting frequency in all the cases was 0.50-0.55.
We have synthesized samples of a multicenter polyfluorene macroinitiator with bromo-alkyl side groups in the monomer units that are able to initiate the polymerization of 2-alkyl-2-oxazolines. Using this macroinitiator, we have conducted the polymerization of 2-ethyl-2-oxazoline. It has been demonstrated that the polymerization of 2-ethyl-2-oxazoline involving the synthesized multicenter polyfluorene macroinitiator is accompanied by a transfer of the chain to the monomer, which leads to the presence of a poly(2-ethyl-2-oxazoline) admixture in the products of polymerization.
We have synthesized samples of macromolecular brushes (comb-like polymers) with side chains attached to a nitrogen-containing backbone via a quaternary base. We have developed methods of the production of polymer brushes by forming quaternary bases during interaction of alkyl iodides with polymers whose elementary unit includes fragments of nitrogen-containing heterocycles such as bipyridine, biquinoline, phenanthroline, antrazoline.
Samples of the characterized macromolecular brushes with a polyimide backbone and side chains comprised of poly(methyl methacrylate) (PI-graft-PMMA) or poly(butyl acrylate) (PI-graft-PBA) were used for the production of network polymer structures. For this purpose a «cross-linker», ethylene glycol methacrylates (EGMA), is introduced into the system. EGMA is able to interact with two reactive terminal groups of the side chains. It has been demonstrated that in case EGMA is introduced into the reaction mixture on the basis of preliminarily isolated samples of PI-graft-PMMA and PI-graft-PBA in comparison to the method of its introduction into a reaction mixture produced as a result of the synthesis of the brush, to form a gel it is necessary to use a higher, by about an order of magnitude, concentration of the cross-linking agent as well as more time or a higher temperature. In the first case for cross-linking it is necessary to achieve a mole ratio of 100-300 between the cross-linking agent and the terminal groups of the side chains in the second case it should be between 5 and 10.
Using methods of molecular hydrodynamics, static and dynamic light scattering, we have researched the behavior of amphiphilic cylindrical brushes near the theta point in varying temperatures. The objects of the research were grafted PI-graft-PMMA and PI-graft-PS copolymers with a polyimide (PI) backbone and side chains comprised by poly(methyl methacrylate) (PMMA) and polystyrene (PS). It has been shown that in θ conditions macromolecules of graft copolymers have an almost spherical shape, as indicated by low values of the characteristic viscosity and the hydrodynamic radii Rh of macromolecules, the absence of a correlation between [h] and the molecular mass (ММ) of samples as well as the nature of the change of the Rh radii with ММ.
The Laboratory has conducted a research of the mechanical behavior of polymer silicone elastomers of a PMMA-PDMS-PMMA composition (PMMA – polymethyl methacrylate, PDMS – polydimethylsiloxane). Samples of the PMMA-PDMS-PMMA triblock copolymer demonstrate a nonlinear nature on the strain-deformation curve. The value of the elastic modulus at the initial region (at a deformation of 20 per cent) has rather low values – 15 kPa. If the deformation increases, a gradual growth of the strain and the elastic modulus of the material is observed, and it reaches its maximum value at a strain of 20,49 kPa and a deformation of about 65 per cent. After this, a sharp drop of the load and the fracture of the sample occurs. It is worth noting that a peculiarity of this material is its strengthening under increasing strain with stretching.
Our researchers have conducted a research of cell and biological compatibility of PMMA-PDMS-PMMA samples with living tissues to determine the possibility of their use in medicine. It has been demonstrated that the studied samples support the adhesion of human dermal fibroblasts (hDF), but the spreading and proliferation of cells on it is impeded. The majority of the cells constantly «test» the mechanical properties of the substrate, which exert chronic stress effects, which is implemented in the form of rearrangements of cyto- and nucleoskeleton, changes in the mechanical properties of the cell itself. It is possible that such structural rearrangements can influence chromatin homeostasis and therefore on DNA replication and gene expression. This results in a decrease in proliferation activity, accelerated aging of cells, their transformation is also possible.
Using the method of the scaling theory of polymer solutions, we have studied the conformational structure and the elastic properties of micromolecular brushes with star-like branching in dilute solutions. It has been demonstrated that depending on the number of side chains originating from one branching point and the length of the spacer, the local conformational structure of the brush is characterized by either a spherical or a cylindrical symmetry of the distribution of the density of monomer units. It has been demonstrated that the dependence of the elastic force on the distance between the ends of the backbone has a characteristic sigmoid shape, which is caused by a conformational rearrangement in the molecular brush on a continuously decreasing scale of the lengths as the applied force increases.
Using the Scheutjens–Fleer self-consistent field method, we have conducted a modeling of the unfolding of a comb-like macromolecule (amphiphilic macromolecular brushes) with a fixed legth of the backbone (M = 101) and linear side chains (n = 10) at a varying distance between neighboring grafted side chains (m = 2...5), placed in a selective solvent (athermic for the backbone and poor for the side chains). It has been shown that the unfolding of the unimolecular micelle formed by a neutral amphiphilic molecular brush occurs through three main stages and is accompanied by a microphase separation into a «head» and a «tail»; in the case of dense grafting and a strong attraction of the side chains towards each other, the deformation curve has a complex sawtooth shape; for a moderately grafted comb-like macromolecule the deformation curve has a shape that is characteristic of a globule from a linear macromolecule, while in a good or «moderately poor» solvent, when an unimolecular micelle is not formed, the stretching of the comb-like macromolecules mostly is determined by the backbone.
Using the Scheutjens–Fleer self-consistent field method, we have researched the conformational properties of polyelectrolyte molecular brushes. The Laboratory has researched a model of comb-like polyelectrolyte consisting of L=61 segments in the backbone and side chains with a length N=30 grafted to every third (l=3) segment of the backbone (the number of side chains is n = 21) with chemically identical backbone and side chains in a poor solvent. It has been shown that the possibility of a redistribution of charged groups in рН-sensitive polyelectrolyte brushes leads to a qualitative difference of their conformations and the conformations of strong polyelectrolytes with the same overall degree of ionization. In the case of a weak polyelectrolyte the side chains are separated into two groups: one group of chains is not charged and forms a dense phase of the nuclei located along the backbone, another group forms a crown that consists of elongated charged side chains. Such two-step conformations manifest themselves in a bimodal distribution of the ends of the side chains around the main axis of the molecule. A transition between a one-step and a two-step conformation can be caused by changes of both рН and the ionic strength of the solution. The bimodality in the distribution of the ends is, in the same manner as the two-step nature of the conformations, absent in the case of a strong comb-like polyelectrolite.
Our researchers have synthesized new macromolecular PE-graft-PMMA brushes with a backbone of complex polyether (PE) and side chains of poly(methyl methacrylate) (PMMA). The structure of the macroinitiator by sulfonyl chloride side groups in each repeating units has been proven by 1Н NMR- and IR spectroscopy. It has been demonstrated that conducting classical ATRP of methylmetacrylate on the produced macroinitiator under the influence of the CuCl/4,4'-dinonyl-2,2'-bipyridyl complex in a chlorobenzene medium at a temperature of 90ºС is the most appropriate setting for the production of PE-graft-PMMA. The conversion of the monomer in 6 and 19 hours in these conditions equals to about 20 and 50 per cent respectively, while the mean degrees of PMMA side chain polymerization in these cases equals to m≈40 and 100.
It has been determined that the produced PE macroinitiators can also be used for the cationic polymerization of 2-alkyl-2-oxazolines. An analysis of kinetic data of the polymerization of 2-ethyl-2-oxazoline on the specified PE macroinitiators shows that the increase of the number of grafted chains occurs in the «living» polymerization mode.
We have conducted a synthesis of series of macromolecular brushes with a polyimide (PI) backbone and side chains of PMMA, poly(n-butyl acrylate) (PBA) and their statistical copolymer. To produce network polymers structures, the terminal units of the side chains of PMMA, PBA or PMMA-st-PBA were augmented by a bifunctional polymer (EGDMA) or poly(ethylene glycol) diacrylate (PEGDA) (Mn=700)) by means of ATRP. We have conducted a cross-linking reaction with a photochemical initiation of a small number of units of bifunctional monomers in terminal units of the side chains of PI-graft-(PMMA-block-(PMMA-stat-PEGDMA) or PI-graft-(PMMA-block-(PMMA-stat-PEGDA)) brushes with the use of benzophenone, benzoin methyl ether, 2-hydroxy-2-methylpropiophenone and phenylbis(2 4 6-trimethylbenzoyl)phosphine oxide as photoinitiators. A film produced using benzoin methyl ether as a photoinitiator had an elastic modulus of 0.93 ± 0.09 GPa, a plastic limit of 15 ± 4 MPa, and a limit deformation leading to breakage amounting to 2.8 ± 0.5 per cent.
Using controlled atom transfer radical polymerization (ATRP) reactions and ring-opening polymerization (ROP), we have synthesized pentablock copolymers (PMMA-block-PCL-block-(PI-graft-PMMA)-block-PCL-block-PMMA), copolymers with a mixed linear-brush topology with a central «brush» block. The structure of the polymers was confirmed by 1H NMR- and IR spectroscopy. The molecular masses of the synthesized samples of copolymers determined by multidetector exclusive liquid chromatography, are in good agreement with sedimentation-diffusion analysis data.
To produce triblock copolymers with a central «brush» block, we have developed a method of the synthesis of heterofunctional PI macroinitiators containing ATRP-initiator groups in every unit as well as terminal groups and that are able to participate in «click»-reactions.
On the basis of a macroinitiator which is polydimethylsiloxane with regularly grafted remnants of 11-bromoundecane (every fourth monomer unit), graft copolymers have been produced with poly(2-isopropyl-2-oxazoline) side chains. Copolymers differ in terms of the length of the grafted chains – 30 and 100 respectively. It has been demonstrated that the polymerization of oxazoline using the specified macroinitiator flows in a living chain mechanism and results in a hybrid polymer with a grafting density of about 0.5.
We have developed a methodology for the synthesis of poluymer brushes with a polyfluorene backbone and poly(2-ethyl-2-oxazoline) side chains by «grafting through», which constitutes the Suzuki polycondensation of the macromonomer with 9-dihexyl-2,7-bis-(trimethyleneborate)fluorene.
We have refined a methodology of the synthesis of copolymers of polyfluorene-graft-polycaprolactone by «grafting from» via the polymerization of caprolactone on a multicenter polyfluorene macroinitiator, poly-9,9-bis(3-hydroxypropyl)-alt-9,9-bis(dioctyl) fluorene. Polymer brushes with side chains of polycaprolactone (polyfluorene-graft-polycaprolactone) have been produced by the ring-opening polymerization of caprolactone on this macroinitiator.
We have produced new promising membrane materials based on new polyamides containing fragments of 6,6’-oxyquinoline, 1,9–anthrazoline and 1,9–anthrazoline quaternized by decyl iodide in the backbone.
Using methods of molecular hydrodynamics and optics we have researched a sample of a grafted PE-graft-PIPOZ copolymer whose backbone was an aromatic PE with an elastic –(CH2)8– spacer and side chains – thermosensitive poly (2-isopropyl-2-oxazoline (PIPOZ). It has been demonstrated that molecules of the studied copolymer have a more symmetric shape and a higher density than molecules of linear poly (2-alkyl-2-oxazoline)s. Such behavior can be explained by the fact that in selective solvents in which the backbone does not dissolve, macromolecules of sparse cylindrical brushes resemble multi-beam star-like molecules in which the core of the star is a collapsed backbone, and the beams are more or less folded side chains that should be viewed as a crown that ensures the solubility of the copolymer.
We have conducted a research of the mechanical behavior, thermophysical and structural characteristics of molecular polysiloxane-graft-PMMA brushes and a comprehensive research of the mechanical and thermal characteristics of sheet samples of ultra-soft elastomer brushes with a PBA backbone, which have statistically grafted polydimethylsiloxane side chains grafted to every 8th link. We have demonstrated a significant increase of the hardness of the material of the series with increasing content of hard polystyrene side chains if their length is constant (70 units). The introduction of polyethylene glycol into the material of the side chains leads to a significant decrease of the hardness. The observed results show the dominant role of elastic deformation in the process of deformation of the researched materials.
In a strong segregation approximation we have developed an analytical theory that allows to describe microphase separation in molten di– and triblock copolymers that contain branches or ring-. The architecture of the blocks is taken into account through their topological relationships. Knowing the value of the topological relationships for a specific architecture allows to determine the location of the block copolymer with a specified composition (the ratio of the volumes of the blocks) on the state diagram and, therefore, to determine the morphology of the microphase-stratified state. The theoretically predicted possibility of controlling the morphology of superstructures by changing the topology of the blocks but without changes in their volume ratio, allows to produce superstructures with characteristics that are unattainable for common linear-linear block copolymers. For example, increasing the extent of the branching of the matrix B block allows to produce stable spherical domains from A blocks even if the volume of an A block exceeds the volume of a B block.
The self-assembly of di- and triblock copolymers containing branching, including molecular brush, blocks in selective solvents as well as the elastic properties of the formed physical and chemically cross-linked gels with subchains made of molecular brushes and conformational transitions in molecular brush blocks caused by changes in the external conditions or applied strains, have been studied using a complex of theoretical methods, including analytical methods of scaling and self-consistent field, the numerical Scheutjens–Fleer self-consistent field method and the molecular dynamics method. It has been demonstrated that increasing the extent of branching of soluble blocks leads to a decrease in the number of block copolymer molecules in a single molecular aggregate (or a physical node of the self-organized mesh).
The extent of swelling of a chemically cross-linked mesh with subchains – molecular brushes – depends on the set of architectural parameters of molecular-brush subchains in a complex and non-monotonous manner.
Molecular brushes with side chains composed of a thermally sensitive weak polyelectrolyte demonstrate the ability to self-organize, forming intramolecular structures of the «necklace» type. The mechanical stretching of molecular brushes with hydrophobic side chains and hydrophilic backbones that form intramolecular micelles in the unperturbed state, provokes intramolecular microphase separation: a party unfolded intramolecular micelle consists of a globular part abd an evenly stretched chain of intramolecular micelles of smaller sizes.
We have developed a method of production of elastic films of network polymer structures based on PI-graft-PMMA macromolecular brushes by modifying PMMA side chains via the introduction of an insignificant number of methacryloyl or acryloyl functional groups into the terminal units. Durable heterogeneous transparent films that can be easily separated from a substrate without cracking and that are not soluble by amide solvents have been produced for compositions prepared on the basis of benzoin methyl ether (photoinitiator) and PEGDA (cross-linker) in a mixture in dioxane (with a concentration of the solution amounting to 8 per cent) with a relative content of the cross-linker ranging from 5 to 50 per cent and a duration of UV exposure amounting to 30-60 minutes.
As a result of the mechanical testing of high-quality samples of films in the single-axis stretching mode has demonstrated that they are characterized by a low firmness (the elastic modulus varies from 65 to 220 MPa) and a rather high deflection limit: at a level of 40-70 per cent at a strength of 2-7 MPa (soft materials). A high elasticity was demonstrated by films produced by exposure of compositions containing 20 to 35 mass per cent of the cross-linker to UV radiation. Films cast from dimethyl fumarate are characterized by values of the elastic modulus, the plasticity limit and the breakage strain that are about twice as high as these characteristics of a film produced using N-MP. The growing hardness of the materials can also be caused by an increasing content of brushes in the composition: the elastic modulus and the plasticity limit of the material with a a 80/20 «brushes/cross-linker» composition containing DMF is 1.55 and 1.7 times higher respectively compared to the same characteristics of a material with a higher concentration of the cross-linker: «brushes/cross-linker» = 70/30 containing DMF.
Our researchers have syntheesized new polycondensation-polymerization macromolecular brushes, namely PI-graft-PCL with a polyimide (PI) backbone and polycaprolactone (PCL) side chains. To produce such brushes, we used a combination of ROP and azide-alkyl cycloaddition (click-reaction) in two variations (1) using polymer-analogous transformations to produce multicenter PI macroinitiator with phenol side groups into a macroinitiator with an initiating hydroxyl group separated from the backbone by a triazole ring and conducting a ring-opening polymerization on it or (2) separately synthesizing macromonomers with required functional groups (polyimide with azide groups in each repeating unit and PCL with terminal alkyl groups) with a subsequent click reaction. Implementing the second approach leads to a more significant growth of the molecular mass, however, linear PCL that does not enter the readtion remains in the system.
We have been continuing work to synthesize ABA-type copolymers of a mixed linear-brush with a central «brush» B block and linear homopolymer A blocks, namely amphiphilic ABA-type triblock PMMA-block-(PI-graft-PMAA)-block-PMMA copolymers with a central B block − a molecular brush with a PI backbone and hydrophilic poly(methacrylic acid) (PMAA) side chains and peripheral hydrophobic chains (A block) of poly(methyl methacrylate) (PMMA).The introduction of PMAA hydrophilic side chains into the brush block of an ABA-type copolymer caused their solubility in ethanol and in a water-alcohol mixture. Using dynamic light scattering, we have demonstrated that at the typical distribution in terms of dimensions of particles for a mixture of amphiphilic block-grafted PMMA-block-(PI-graft-PMAA)-block-PMMA brushes in ethanol we could observe one type of particles whose average size is about Rh = 12 nn, which is typical of molecular-dispersion solutions.
The Laboratory has developed a methodology for the synthesis of new amphiphilic polymer brushes with a polyfluorene backbone and poly(methacrylic acid) side chains. The produced brushes are not soluble in water but soluble in alcohols (methyl and ethyl alcohol). The study of the spectra of the photoluminescence of solutions of macroinitiator, polymer brushes with poly(tert-butyl acrylate) and poly(methacrylic acid) side chains demonstrated that the intensity of the luminescence of polymer brushes is higher than the intensity of the macroinitiator despite the fact that the mass fraction of the luminescent polymer is higher in the macroinitiator in comparison with polymer brushes in which only the backbone luminesces. Moreover, when comparing the photoluminescence spectra of polymer brushes with various lengths of side chains it was demonstrated that increasing the lengths of side chains leads to a decrease in the intensity of both absorption and luminescence.
Our researchers have performed a synthesis of polyamide-graft-polyoxazoline brushes. It has been established that the application of noncatalytic acceptor polycondensation with the use of propylene oxide as the acceptor allows to produce polyamides containing lateral sulfonyl chloride groups. On the basis of a microinitiator that is a carbosylane dendrimer which is fully functionalized along the periphery by remnants of 11-bromoundecane we have produced a grafted copolymer with poly(2-isopropyl-2-oxazoline) side chains. An analysis of the possibility of using a number of solvents to conduct a grafting polymerization of oxazolines has shown that the reaction proceeds in the most efficient way in a sulfonate solution at a temperature of 90-110 °С. As follows from gel permeation chromatography (GPC) data, the produced polymers are characterized by rather narrow monomodal distributions and have molecular masses of Mw = 1.82×104 and Mw=1.45×104 at a polydispersity ratio of Đ=2.5 for both polymers. Water solutions of the synthesized comb-like poly(2-alkyl-2-oxazolines) at increased temperatures undergo a coil–globule transition which is accompanied by a loss of solubility of the polymer. The dependence of the phase transition temperature on the concentration is weakly expressed, however, in the case of a polymer with oligo-2-isopropyl-2-oxazoline side fragments in a wide range of concentrations (0.5 – 5 per cent) lies in the region of «physiological» temperatures.
The Laboratory has synthesized new polyamides containing 6,6’-oxydiquinoline fragments in their backbone and distinguished by the length of side ester groups. The synthesized initial compounds and polymers have been investigated using IR and NMR spectroscopy, scanning electron microscopy. We have studied the extent of swelling of polymers in various solvents and the boundary wetting angles, the thermal and deformation-strength characteristics. Membranes have been produced from all the synthesized polymers and a pervaporation separation of the mathanol-heptane mixture has been performed at room temperature. It has been demonstrated that the synthesized polyamides with aliphatic side groups are of interest as materials for membrane technologies.
We have studied the behavior of polymerization-polycondensation stimulus-sensitive grafted APE-graft-PIPOZ in solutions. The backbone of APE-graft-PIPOZ was aromatic polyester (APE) and the side chains were poly (2-isopropyl-2-oxazoline) (PIPOZ). It was shown that in a selective solvent – good for PIPOZ, while APE does not dissolve in it – macromolecules of APE-graft-PIPOZ that in their shape resemble a star due to the fact that the backbone tends to depart from the solvent, while the side chain shield APE from the solvent. For the researched molecular brush the lower critical solution temperature (LCST) is close to 20 °С, which is significantly lower than typical LCST values for linear PIPOZ. The decrease of the LCST for APE-graft-PIPOZ is caused both by the higher hydrophobicity of APE-graft-PIPOZ and the difference in the characteristics, the architecture of macromolecules of the compared polymers. For comparison, we have studied the self-organization processes in water solutions of the cylindrical brush CD1-PIPOZ with four PIPOZ beams, whose core is carboxylane dendrimer (CD1). The phase transition temperature (Tpt) of CD1-PIPOZ is almost 30°C higher than the phase transition temperature of APE-graft-PIPOZ and is close to the Tpt temperatures for linear PIPOZ. The difference in Tpt for the spherical cylindrical brush is caused by a difference in the hydrophobicity of APE-graft- PIPOZ and CD1-PIPOZ macromolecules, аs well as a higher intramolecular density of the cylindrical brush.
To determine the impact of the parameters of the architecture and the structural parameters of macromolecules on the self-organization of three-component brushes in solutions, we have studied the grafted (PI-graft-(PMAA-block-PMMA)) copolymers with a polyimide (PI) backbone and side chains made of an amphiphilic block copolymer, poly(methyl methacrylate) (PMMA) and poly(methacrylic acid) (PMAA). It has been demonstrated that the behavior of PI-graft-(PMAA-block-PMMA) samples in solutions was determined by the structural parameters of the molecular brush and the nature of the solvent. In molecular-disperse solutions (in chloroform) molecules of the synthesized graft copolymers had compact dimensions and resembled core-shell structures, whose core was a strongly compressed PI chain, while the shell is formed by PMAA-block-PMAA side chains. The aggregation of macromolecules was observed in the majority of solvents. The size of the aggregate depended on the thermodynamic quality of the solvent with respect to the component of the copolymer as well as on the parameters of the architecture of the macromolecules. In particular, in ethanol a decrease of the PMMA content leads to a decrease of the size of the aggregates, while an elongation of the outer PMMA block caused a decrease in the hydrodynamic radius. In this solvent the aggregates had a rather symmetrical shape that is close to spherical.
Our researchers have studied the conformational transitions in molecular brushes with semi-rigid backbones and side chains consisting of a thermally sensitive weak polyelectrolyte and we have demonstrated the effect of intramolecular nanostructuring when the рН of the solution of the concetration of salt changes. An analytical approach to the description of conformations of hierarchically branched macromolecules of the molecular brush type with dendrite- or comb-like-branching side chains.
Using methods of the analytical theory as well as numerical self-consistent method and computer modeling relying on Brownian dynamics, we have studied the structure of intramolecular micelles formed in a selective solvent by molecular brushes with a soluble backbone and insoluble side chains as well as intramolecular conformational transitions occurring in such brushes during stretching. We have found the dependencies of elastic force on strain and established systematic links between the architecture of molecular brushes (grafting density and side chain length) as well as the quality of the solvent and the shapes of the deformation curves. Our researchers have predicted the effect of formation of a necklace of intramolecular micelles, which is caused by the stretching of the molecular brush with densely grafted side chains. Simplified theoretical models have been proposed that allow to explain the dependency of the dimensions and the extent of aggregation of the micelles forming the necklace on the parameters of the brush.
In the scaling approximation we have developed the theory of structural and elastic properties of swelling networks formed by molecular brushes with covalently cross-linked ends of the backbones. We have identified characteristic scaling modes and obtained asymptotic power laws of the properties of the network on the set of the basic architectural characteristics – the extents of polymerization of the backbone and the side chains as well as the density of grafting of side chains. We have developed computer software for the numerical modeling of equilibrium swelling as well as the elastic behavior of gels formed by molecular brushes with cross-linked terminals of the backbones in a good solvent and observed the dependence of the elastic response on the deformation with different compositions of molecular brushes – subchains of the network.
Our researchers have produced new triblock ABA-type PMMA-block-(PI-graft-PMAA)-block-PMMA copolymers of mixed linear-brush topology using an optimized two-stage methodology.
We have developed a method for the synthesis of molecular brushes with polyimide (PI) backbones and poly(ε-caprolactone) (PCL) side chains.
In this project, cellulose macromolecules (C) were used as a backbone to produce C-graft-PMAA molecular brushes with poly(methacrylic acid) (PMAA) side chains. It has been shown that water-soluble C-graft-PMAA molecular brushes are efficient nanocontainers for the fast and selective transport of cyano porphyrazine agents for photodynamic therapy and diagnostics to tumor cells.
We have produced new PF-graft-PTBMA and PF-graft-PMAA brushes with polyfluorene backbones and side chains consisting of poly(tert-butyl methacrylate) (PtBMA) and poly(methacrylic acid) (PMAA) and studied the quantum yields of their luminescence. It has been shown that an increase of the length of the side chains leads to an increase in the quantum yield of PF-graft-PTBMA, which is probably related to a decrease of the extent of the aggregation of these brushes, and to a decrease of the outout of PF-graft-PMAA due to an increase of the extent of aggregation due to the formation of intermacromolecular hydrogen bonds between poly(methacrylic acid) chains.
The Laboratory has refined a methodology of the synthesis of polyfluorene macroinitiators that allows to variate their molecular mass, luminescence spectrum and attach the ATRP initiator groups on a longer hexyl spacer that reduces the steric hindrance to the subsequent synthesis of polyfluorene brushes. This method also allows to efficiently clean polyfluorene, while the monomer can be produced from cheaper substances.
Our researchers have studied the behavior of stimuli-sensitive graft copolymers in molecular disperse solutions of APE-graft-PAOZ graft copolymers whose backbone is rigid-chain aromatic polyester (APE) and the side chains are made of poly(2-alkyl-2-oxazoline), more precisely, poly (2-ethyl-2-oxazoline) (PEOZ) and poly(2-isopropyl-2-oxazoline) (PIPOZ).
It has been shown that in water solutions of APE-graft- PEOZ at low temperatures there exists one type of scattering objects – macromolecules of the copolymer. In the case of APE-graft-PIPOZ in solutions, we have found only aggregates that are formed by interaction of hydrophobic APE of the backbones. The difference in the behavior of APE-graft-PEOZ and APE-graft-PIPOZ is caused by various extents of shielding of the APE backbone from the solvent in which it does not dissolve. Long PEOZ chains are reasonably good at «shielding» the backbone from the solvent, and at low temperatures water solutions of APE-graft-PEOZ are molecularly disperse. The length of the PIPOZ chains are insufficient for good shielding of the backbones from the solvent, and the APE-graft-PIPOZ copolymer dissolves forming large aggregates. The hydrodynamic radius of the discussed particles Rh increased with the increase of the concentration of the polymer, which is confirmed by atomic-force microscopy.
We have synthesized molecular brushes by atom transfer radical polymerization (ATRP) of macromonomers of poly(dimethylsiloxane metacrylate) (PDMSMA) with controlled shares of poly(ethylene glycol) metacrylate (PEGMA) macromonomeres with terminal hydroxyl (OH-) or azide (N3-) groups that were cross-linked with the use of a bifunctional cross-linking agent. A study of the mechanical properties of fully cured elastomers has demonstrated that the architecture of the network of molecular brushes allows to independently adjust the softness, the stretchability of a region of the chain between the cross-links determined by a theoretical elongation at fracture demonstrates good agreement with experimental values of a macroscopic sample, which suggests a homogeneous structure of the networks, the structural Young's modulus of the elastomers corresponds with the theoretically forecasted correlation and the mechanical properties are «invariant» with regard to the chemical structure of the cross-linked groups.
Education and career development:
Ten Candidate of Science have been prepared and defended.
Collaborations:
Razuvaev Institute of Organometallic Chemistry of the Russian Academy of Sciences, Institute of Biology and Bio medicine of the N. I. Lobachevskiy Nizhniy Novgorod State University, ITMO University, N. S. Enikolopov Institute of Synthetic Polymer Materials of the Russian Academy of Sciences, Lomonosov Moscow State University, Peter the Great St.Petersburg Polytechnic University (Russia), DWI Leibniz-Institute for Interactive Materials, Institute of Physical Chemistry and Polymer Physics, Institute of Physics and Astronomy of the University of Potsdam (Germany), University of North Carolina at Chapel Hill (USA), Institute of Analytical Sciences and Physico-Chemistry for Environment and Materials (France), Wageningen University & Research (the Netherlands), Charles University, Institute of Macromolecular Chemistry of the Czech Academy of Sciences (Czech Republic), University of Toronto (Canada): joint research.
