Modern methods for studying polymer complexes in aqueous and organic solutions

This review summarizes published data concerning modern physicochemical methods used to study complexation processes of polymers in solutions. Some of them—dynamic light scattering, nanoparticle tracking analysis, transmission electron microscopy, cryotransmission electron microscopy, atomic force microscopy, small-angle neutron scattering, analytical-velocity sedimentation, and luminescence methods—make it possible to gain insight into the structure of polymer complexes, while the other methods, such as isothermal titration calorimetry and surface plasmon resonance, provide an opportunity to assess the intensity of specific interactions between complex components

Density Functional Theory Study on the Aggregation and Dissociation Behavior of Lithium Chloride in THF and Its Interaction with the Active Centers of the Anionic Polymerization of Methyl Methacrylate and Styrene

ABSTRACT: The structure of LiCl in tetrahydrofuran (THF) solution and its effect on the structure and stability of active sites of the anionic polymerization of methyl methacrylate (MMA) and styrene (St) was studied using the quantum-chemical density functional theory (DFT) approach. In the case of MMA anionic polymerization, it was found that LiCl forms stable mixed aggregates with ester enolates which model the PMMA living chain ends, thus preventing them from self-aggregation. They may even stabilize more reactive zwitterionic structures of these chain ends. The dissociation of solvated LiCl dimers to form Li + (THF)4 cations is slightly endothermic in THF, while scavenging of Li + (THF)4 by LiCl dimers to produce more stable quintuple cations [(THF)3Li-Cl-Li(THF)2-Cl-Li(THF)3] + is even exothermic. Therefore, if the concentration of LiCl exceeds a certain threshold value, Li + (THF)4 cations should effectively be scavenged by LiCl dimers. Thus, increasing LiCl concentration below the threshold concentration should lead to an increase in the concentration of free Li + (THF)4 cations. In the anionic polymerization of styrene in the presence of LiCl this results in the suppression of PSt-Li chain end dissociation due to the common ion effect, slowing down the polymerization. Further addition of LiCl above the threshold concentration should decrease the concentration of free Li + (THF)4 cations, leading to enhanced PSt-Li chain end dissociation, thus increasing the polymerization rate, in agreement with kinetic data reported in the literature

Molecular mobility in comb-like copolymethacrylates with chalcone-containing side-chains

[EN] The molecular mobility of comb-like copolymers of amyl methacrylate with N-methacryloyl-(4-amino-4'-bromochalcone) with various concentrations (20, 30, 40, 50 and 60 mol%) of chalcone-containing comonomer was studied using dielectric spectroscopy. It was found that chalcone chromophores participate in two forms of molecular mobility: cooperative motion in the rubbery state (delta-relaxation) and local motion in the glassy state (beta-relaxation). In addition, alpha-, beta(1)- and gamma-processes, being related to cooperative segmental mobility, to local motion of ester groups adjacent to the backbone and to local motion of terminal side-groups, respectively, were evident. The molecular mobility of the beta(1)-, beta-and gamma-processes changed slightly with the concentration of chromophore groups. For the delta- and alpha-processes, the glass transition temperatures, T(delta) and T(g), increased with the molar fraction of chalcone groups, the difference between them remaining nearly constant (ca 55 degrees C). The Td values obtained should be considered as optimal temperatures for the corona-poling of the chromophore-containing polymers for the preparation of second-order nonlinear optical polymer films with non-centrosymmetric arrangement of chromophore groups. (C) 2011 Society of Chemical IndustryThis research was supported by a grant of the Polytechnic University of Valencia (resolution of UPV from 13.05.08) and a grant of CICYT (MAt2008-06725-C03-03).Nikonorova, NA.; Díaz Calleja, R.; Yakimansky, AV. (2011). Molecular mobility in comb-like copolymethacrylates with chalcone-containing side-chains. Polymer International. 60(8):1215-1221. https://doi.org/10.1002/pi.3065S1215122160

Agricultural Applications of Superabsorbent Polymer Hydrogels

This review presents data from the past five years on the use of polymeric superabsorbent hydrogels in agriculture as water and nutrient storage and retention materials, as well as additives that improve soil properties. The use of synthetic and natural polymeric hydrogels for these purposes is considered. Although natural polymers, such as various polysaccharides, have undoubted advantages related to their biocompatibility, biodegradability, and low cost, they are inferior to synthetic polymers in terms of water absorption and water retention properties. In this regard, the most promising are semi-synthetic polymeric superabsorbents based on natural polymers modified with additives or grafted chains of synthetic polymers, which can combine the advantages of natural and synthetic polymeric hydrogels without their disadvantages. Such semi-synthetic polymers are of great interest for agricultural applications, especially in dry regions, also because they can be used to create systems for the slow release of nutrients into the soil, which are necessary to increase crop yields using environmentally friendly technologies

Self-Assembly of Molecular Brushes with Polyimide Backbone and Amphiphilic Block Copolymer Side Chains in Selective Solvents

Three-component molecular brushes with a polyimide backbone and amphiphilic block copolymer side chains with different contents of the “inner” hydrophilic (poly(methacrylic acid)) and “outer” hydrophobic (poly(methyl methacrylate)) blocks were synthesized and characterized by molecular hydrodynamics and optics methods in solutions of chloroform, dimethylformamide, tetrahydrofuran and ethanol. The peculiarity of the studied polymers is the amphiphilic structure of the grafted chains. The molar masses of the molecular brushes were determined by static and dynamic light scattering in chloroform in which polymers form molecularly disperse solutions. Spontaneous self-assembly of macromolecules was detected in dimethylformamide, tetrahydrofuran and ethanol. The aggregates size depended on the thermodynamic quality of the solvent as well as on the macromolecular architectural parameters. In dimethylformamide and tetrahydrofuran, the distribution of hydrodynamic radii of aggregates was bimodal, while in ethanol, it was unimodal. Moreover, in ethanol, an increase in the poly(methyl methacrylate) content caused a decrease in the hydrodynamic radius of aggregates. A significant difference in the nature of the blocks included in the brushes determines the selectivity of the used solvents, since their thermodynamic quality with respect to the blocks is different. The macromolecules of the studied graft copolymers tend to self-organization in selective solvents with formation of a core–shell structure with an insoluble solvophobic core surrounded by the solvophilic shell of side chains

Novel Amphiphilic Polyfluorene-Graft-(Polymethacrylic Acid) Brushes: Synthesis, Conformation, and Self-Assembly

Novel polyfluorene polymer brushes with polymethacrylic acid side chains were obtained by atom transfer radical polymerization (ATRP) and activator generated by electron transfer (AGET) ATRP of tert-butyl methacrylate on polyfluorene multifunctional macroinitiator, followed by protonolysis of the tert-butyl groups of the side chains. Kinetics of polymerization and molecular weights were fully characterized. These polymer brushes luminesce in the blue region of the spectrum with high quantum yields (0.64–0.77). It was shown that the luminescence intensity of polymer brushes is higher than the luminescence intensity of the macroinitiator (0.61). Moreover, due to their amphiphilic nature, they can form unimolecular micelles when an alcohol solution of the polymer brush is injected into water. These properties can potentially be used in drug delivery and bioimaging

Quantum Dot–Polyfluorene Composites for White-Light-Emitting Quantum Dot-Based LEDs

International audienceColloidal quantum dots (QDs) are a promising luminescent material for the development of next generation hybrid light-emitting diodes (QDLEDs). In particular, QDs are of great interest in terms of the development of solid-state light sources with an emission spectrum that mimics daylight. In this study, we used CdSe(core)/ZnS/CdS/ZnS(shell) QDs with organic ligands mimicking polyfluorene and its modified derivatives to obtain QD-polymer composites emitting white light. We found that the emission of the composites obtained by spin-coating, being strongly dependent on the chemical structure of the polymer matrix and the QD-to-polymer mass ratio, can be accurately controlled and adjusted to bring its emission spectrum close to the spectrum of daylight (CIE coordinates: 1931 0.307; 0.376). Moreover, the light emission of these composites has been found to be temporally stable, which is due to the minimal structural instability and volume-uniform charge and energy transfer properties. Thus, the use of the synthesized polyfluorene-based organic ligands with controllable chemical structures adaptable to the structure of the polymer matrix can significantly increase the stability of white light emission from QD composites, which can be considered promising electroluminescent materials for fabrication of white QDLEDs