Poly(diallyldimethylammmonium chloride) samples were prepared in a wide range of molecular weight by radical polymerization at low degree of conversion to realize undisturbed molecular weight distributions. Determination of the molecular and thermodynamic parameters by viscometry, osmometry, light scattering, gel permeation chromatography (GPC) and analytical ultracentrifugation (AUC) give acceptable agreement. The high values of the second virial coefficient would result in a corresponding excluded volume. However, the dependencies of the radius of gyration and the second virial coefficient on molecular weight do not reflect the excluded volume effect. The discrepancy can be explained by a dominating Donnan contribution. Taking into account the polydispersities of the samples, a Kuhn segment length of 5 nm was determined for poly(diallyldimethylammonium chloride) in 0.5 M NaCl solutions. [η]‐M relations were obtained for 1 M NaNO3, 1 M NaCl and 0.5 M NaCl solutions.
Ionic liquids based on imidazolium, pyridinium, and alkylammonium salts were investigated as solvents in free radical polymerization of the model monomer n-butyl methacrylate. The properties of the ionic liquids were systematically varied by changing the length of the alkyl substituents on the cations, and by employing different anions such as tetrafluoroborate, hexafluorophosphate, tosylate, triflate, alkyl sulfates and dimethyl phosphate. Results were compared to analogous polymerizations in toluene and in bulk. The solvents have no detectable influence on polymer tacticity. However, the molar masses obtained and the degree of polymerization, respectively, are very sensitive to the choice of the solvent. The degrees of polymerization are significantly higher when polymerizations were carried out in ionic liquids compared to polymerization in toluene, and can even exceed the values obtained by bulk polymerization. Imidazolium salts unsubstituted at C-2 result in an increase in the degree of polymerization of the poly(butyl methacrylate) with increasing viscosity of these ionic liquids. Methyl substitution at C-2 of the imidazolium ion results in an increase in the viscosity of the ionic liquid and in a viscosity independent degree of polymerization of the poly(butyl methacrylate). Ionic liquids based on imidazolium salts seem preferable over pyridinium and alkylammonium salts because of the higher degree of polymerization of the poly(butyl methacrylate)s obtained in the imidazolium salts. The glass transition temperatures and thermal stabilities are higher for poly(butyl methacrylate)s synthesized in the ionic liquids compared to the polymer made in toluene.
A simple preparation method of ordered multilayer films of submicrometer- and micrometer-sized monodisperse latex particles in the broad range of 0.2−2.5 μm is reported. The films were prepared from aqueous suspensions by vertical deposition at elevated temperatures. Both hydrophobic polystyrene and hydrophilic core−shell particles allowed good array formation. Three-dimensional lattices were proved by transmission and reflectance vis−NIR−IR spectroscopy. Well-developed Bragg peaks up to 5000 nm have been registered. An observation of Fabry−Perot resonance signals in the spectra also confirms the good array quality. Optical properties of the gratings were investigated by laser diffraction and by diffraction using an optical microscope equipped with a Bertrand lens.
Ionically modified LCST polymers were synthesized by free radical copolymerization of N-isopropylacrylamide (NIPAM) with various cationic, anionic, and amphoteric comonomers, resulting in products with comparable molecular masses and charge concentrations. The temperature-dependent phase transition behavior of the copolymers was investigated in water, aqueous sodium chloride solutions, and mixtures of water with dimethylformamide (DMF) using light transmission measurements, static light scattering, viscometry, and sedimentation experiments in an analytical ultracentrifuge. The LCST of the cationic modified copolymers remains unchanged compared with the homopolymer, but it is increased as a result of an amphoteric or anionic modification. Phase transitions are accompanied by conformational changes followed by aggregation processes. These changes are enhanced in the presence of salt. The phase transition of poly-NIPAM-co-MADAMBQ ((methacryloyloxy)ethyl)dimethylbenzylammonium chloride) in 0.5 M NaCl was studied in detail investigating the temperature dependence of molecular parameters as intrinsic viscosity, particle mass, radius of gyration, second virial coefficient, and sedimentation coefficient.
Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30-35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30 A degrees C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations
The influence of various levels of succinylation on the structure of the legumin from pea seed has been studied by the techniques of sedimentation velocity, viscometry, fluorescence and circular dichroism spectroscopy, as well as dynamic light scattering. The protein dissociates gradually into the 3s subunit forming a 7s intermediate. At a level of 75 -80% succinylation, sudden unfolding of the protein occurs characterized by drastic changes in viscometric and spectroscopic properties. The fluorescence spectra point to the formation of a novel organized structure at a moderate degree of modification before the molecular unfolding takes place.The succinylated subunit was shown to have a sedimentation coefficient of 3.2S, a diffusion coefficient of 5.03 x cm2 . s p l a Stokes' radius of 4.24 nm, a partial specific volume of 0.703 ml/g, an intrinsic viscosity of 0.13 dl/g, a molar mass of 52.2 kDa and a frictional ratio of 1.74.Legumin is one of the main storage proteins in the seeds of pea (Pisum sativum L.). It belongs to the group of the socalled l l S globulins, having sedimentation coefficients between lls and 14S, and molecular masses between 300 kDa and 400 kDa [l]. These proteins possess an oligomeric structure characterized by an arrangement of six subunits (3s components) [2 -41. The molecular mass of pea legumin was reported by different authors to be in the range 330 -410 kDa [l, 5, 61. By means of small-angle X-ray scattering, a value of 359 f 25 kDa was obtained [7]. Disulphide-bonded polypeptide pairs with molecular mass 54 kDa constitute most of the 3s subunit of the legumin [8]. In addition, polypeptide pairs varying in molecular mass over 35-58 kDa have been observed which associate in various ways to give rise to different molecular forms of legumin IS].Due to very similar quaternary structures [9, lo], the 11s plant proteins show an analogous behaviour dissociating into subunits [l 11. Therefore, the decay of oligomeric structure by an increase of negative charge caused by succinylation effects similar changes in the structure of different 11s proteins. Although there are specific differences in the dissociation behaviour of the peanut [12], sunflower seed [13] and rape seed [14] 11s globulins, a step-by-step decay of the native structure, and a marked change in conformation at a critical step of succinylation, were observed in each case.The present paper deals with the effect of succinylation on the oligomeric structure of the 11s globulin (legumin) from pea. Structural changes of the protein were followed using ultracentrifugation, viscometry, circular dichroism and fluorescence spectroscopy. The physicochemical properties of the dissociation products, including molecular mass and shape, were investigated by a combination of hydrodynamic methods, including dynamic light scattering. MATERIALS AND METHODSLegumin was isolated and purified according to Gueguen et al. [15]. Lyophilized preparations containing small amounts of aggregated material were purified additionally by gel filtration on a ...
Monolayers of monodisperse colloidal particles are formed by self-assembly. Such 2-D particle arrays are interesting objects for applications as lithographic masks, optical gratings, multilens arrays, antireflecting surface, synthetic membranes, data storage media, etc. Different techniques were proposed for the fabrication of such arrays. One approach uses monolayer film formation in a thin wetting film. In the simplest modification it consists of slow drying of the particle suspension prepared as a thin film on a solid or liquid substrate. 1-7 More sophisticated modifications require special apparatus. 8-10 Another approach relies on electrophoretic deposition of particles onto an electrode. 11 Both approaches have a drawback in the difficulty to control monolayer formation, because areas thicker than a monolayer can be formed. On the other hand, it is possible to build a monolayer on the liquid-air interface. Colloidal particles apparently can be trapped at the liquid surface as a result of the electrostatic and surface tension forces. 12-15 However, application of the Langmuir-Blodgett (LB) technique to colloidal particles led to sub-monolayers with a coverage not more than 80%. 16,17 Only recently Tredgold and coworkers 18 reported on the successful Langmuir-Schaefer transfer of monolayers of silica particles modified with 3-aminopropyl groups. However, the properties of these arrays were not reported in detail. Kondo et al. 19 were able to fabricate close packed 2-D arrays of silica particles transferred from benzene/air interface by a simple technique without using a LB trough. However, this requires an additional chemical step of silica particle modification by alkoxylation. Only particles modified with dodecyl chains (thus highly hydrophobic) formed ordered close packed monolayers. The authors 19 believe that the monolayer formation involves a two-stage process with particles laterally moving on the solid substrate to form finally close packed array. Recently Aveyard et al. 20 investigated the monolayer behavior of polystyrene (PS) particles at the water/octane interface and found a formation of highly ordered arrays of large 1.5 and 2.6 µm particles. The particles were highly repulsive in contrast to the behavior at the air/water interface. In this work no attempt to the transfer of particles onto a solid substrate was reported. Thus it seems that despite many years of studies of the behavior and aggregation of colloidal particles at the water/ air interface 12-23 there is still a lack of data on the transfer of the monolayer onto the solid substrates.The recent results 18,20 led us to a new very simple and fast method of the fabrication of close packed arrays of large latex and silica particles. Large particles have also the advantage to be easily imaged by optical microscopy. We used monodisperse 0.74 and 1.2 µm polystyrene (PS) particles (obtained according to ref 24 by an emulsifierfree, aqueous radical polymerization), 0.94 µm polystyrene-2-hydroxyethyl methacrylate (PS-HEMA) particles, 1.2 and 1...
2,2,6,6-Tetramethylpiperidine-1-yloxyl derivatives substituted with either hydrogen bonding [-OH, -OSO(3)H] or ionic [-OSO(3) (-)Na(+), -OSO(3) (-)K(+), N(+)(CH(3))(3)I(-), N(+)(CH(3))(3) N(-)(SO(2)-CF(3))(2)] substituents are investigated in 1-butyl-3-methylimidazolium tetrafluoroborate over a wide temperature range covering both glassy and viscous states. The Vogel-Fulcher-Tammann equation describes the temperature dependence of the ionic liquid viscosity. Quantum chemical calculations of the spin probes at the UB3LYP/6-311(2d,p++) level are done to describe the dependence of the spin density on nitrogen on the substitution pattern of the 4-position of the probe. The results of these calculations are also used to understand the experimental results obtained by applying the Spernol-Gierer-Wirtz theory to analyze the viscosity dependence of the rotational correlation time of the spin probes. Significant differences are found between 2,2,6,6-tetramethylpiperidine-1-yloxyl and its derivatives containing substituents that are able to form hydrogen bonds with the ionic liquid. Moreover, derivatives substituted with ionic groups at the 4-position have a large effect on temperature-induced solvent viscosity, as this is particularly dependent on the nature of the substituent at the 4-position. These dependencies include the temperature region that can be used to describe interactions between the spin probes and the ionic liquid, diffusion into the free volume during non-activated (neutral spin probes) and activated (charged spin probes) processes. Additional parameters are the radii of the ionic liquid and the spin probes, which are calculated and measured approximately. In addition, the temperature dependence of the isotropic hyperfine coupling constants of the spin probes results in information about the micropolarity of the ionic liquid. At room temperature, this is comparable to that of the solvent dimethylsulfoxide.
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