Preparation and characterization of crosslinked PMMA latex particles stabilized by grafted copolymer

 The preparation of polymethyl methacrylate lattices stabilized by polyhydroxystearic acid and crosslinked with ethylene glycol dimethylmethacrylate (EGDM) has been studied. Crosslinking is a new development in the synthesis of PMMA latex. The particles are monodisperse when the concentration of EGDM ranges from 0.33 to 1.44%. The lattices are stable in aromatic and aliphatic solvents. Swelling occurs due to penetration of solvent molecules into the latex. The degree of swelling is calculated by viscosity and by dynamic light scattering measurements. Received: 30 January 1997 Accepted: 2 June 1997     

Preparation of the stabilized glycoenzymes by cross-linking their carbohydrate chains

Each of the three high-mannose type glycoproteins studied, acid phosphatase, invertase, and glucose oxidase, could be specifically cross-linked through its carbohydrate chains. The procedure involves periodate oxidation of carbohydrate residues followed by reaction of the generated aldehyde groups with adipic acid dihydrazide as a cross-linker. The amount and size as well as solubility of the formed polymers could be efficiently controlled by varying the reaction conditions, i.e., the oxidation degree and the concentrations of glycoproteins, cross-linker, and hydrogen ions during the cross-linking reaction. It was found that the quantity and size of polymers increased with oxidation degree and protein concentration and by lowering the pH. When the protein concentration was above and pH below certain values, depending on the glycoenzyme, insoluble polymers formed. The soluble cross-linked polymers retained a high level of original activity, and the minor decrease in specific activity noticed was shown to occur during the periodate oxidation step. The cross-linked glycoenzymes are much more resistant to denaturation by high temperature and by changes in pH, demonstrating the usefulness of this method in preparation of the stabilized glycoprotein derivatives.     

A Review of Temperature Influence on Adsorption Mechanism and Conformation of Water Soluble Polymers on the Solid Surface

The temperature effect on adsorption behavior of water soluble polymer and structure of its adsorption layer formed on the solid surface is presented. The main reasons for such problem explanation are wide application possibilities of stabilization-flocculation properties of polymers in many technological and ecological processes and very poor knowledge about temperature dependences of high-molecular compounds adsorption on the solid surface. To systematize the information about the effect of temperature on polymer chain conformation on the adsorbent surface the following aspects were considered: thermodynamic and physicochemical characteristics of polymer solutions, stabilization-flocculation properties of polymers in the dispersed systems, and presentation of respective experimental results. The theoretical and experimental evidence of the temperature effect on polymer macromolecule conformation on the solid surface presented in the article can contribute to better knowledge and understanding of the adsorption process at the metal oxide-polymer solution interface in the temperature function.     

Influence of poly(ethylene oxide) brushes on the rheological properties of MgO colloidal suspensions in water

A combined experimental and multiscale simulation study of the influence of polymer brush modification on interactions of colloidal particles and rheological properties of dense colloidal suspensions has been conducted. Our colloidal suspension is comprised of polydisperse MgO colloidal particles modified with poly(ethylene oxide) (PEO) brushes in water. The shear stress as a function of shear rate was determined experimentally and from multiscale simulations for a suspension of 0.48 volume fraction colloids at room temperature for both bare and PEO-modified MgO colloids. Bare MgO particles exhibited strong shear thinning behavior and a yield stress on the order of several Pascals in both experiments and simulations. In contrast, simulations of PEO-modified colloids revealed no significant yielding or shear thinning and viscosity only a few times larger than solvent viscosity. This behavior is inconsistent with results obtained from experiments where modification of colloids with PEO brushes formed by adsorption of PEO-based comb-branched chains resulted in relatively little change in suspension rheology compared to bare colloids over the range of concentration of comb-branch additives investigated. We attribute this discrepancy in rheological properties between simulation and experiment for PEO-modified colloidal suspensions to heterogeneous adsorption of the comb-branch polymers.     

The effect of the steric hindrance on metallic cation conduction in polymer electrolytes

2,6-Di-t-butylphenol and oligo(ethylene oxide) bound covalently to polyisocyanate were synthesized and characterized. The ionic conductivities of their Li, Na, and K phenolates were studied at various temperatures. The conductivities were in the range of 10^?7?10^?5 S/cm at 30°C. The conductivity of Na and K salts was approximately 10² greater than that of the Li salts. The t-butyl groups serve to dissociate K and Na ions from the phenoxide. The cations, therefore, are more mobile as a result increasing the conductivity. The temperature dependence of ionic conductivity suggests that the migration of ions is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Tammann–Fulchere plots. The polyisocyanate backbone is a rather stiff structure, however, a flexible oligo(ethylene oxide) side chain forms complexes with metal ion. Since the ion transport is associated with the local movement of polymer segments, the rigidity of the polymer backbone does not have much influence on the ion mobility.     

Elastic steric stabilization of polyethylene-asphalt emulsions by using low molecular weight polybutadiene and devulcanized rubber tire

Emulsions containing 3% polyethylene were stabilized against coalescence in an asphalt medium by low molecular weight virgin polybutadiene and recycled styrene-butadiene stabilizers. The recycled styrene-butadiene steric stabilizer precursor was obtained as a thermo-mechanical devulcanized ground rubber tire in asphalt. The low molecular weight butadiene and styrenebutadiene rubbers were in situ reacted with sulfur in order to increase the compatibility of the stabilizer with the asphalt phase.Because of the high molar volume of the asphalt phase and the similarity in contact energy between stabilizer and matrix phase, it is assumed that the stabilization is caused by entropic effects only. The fundamental aspects of elastic stabilization of polyethylene-asphalt emulsions are discussed. The total interaction free energy profile between the polyethylene particles shows that the efficiency of the steric stabilizer formation reaction can be improved significantly.The use of devulcanized rubber tire as a replacement for the virgin polybutadiene precursor in the in situ stabilization process can significantly reduce the cost of the technology.     

Effect of surfactants on the fluorescence spectra of water-soluble MEHPPV derivatives having grafted polyelectrolyte chains

Poly(2-methoxy-5-[2′-ethylhexyoxy]-1,4-phenylenevinylene) (MEHPPV) derivatives with polyacrylic acid (PAA) chains grafted onto their backbone were found to be water soluble, and they exhibited a dramatic increase in their fluorescence intensity in the presence of a variety of surfactants, even at concentrations far below their critical micelle concentrations (CMC). This increase was accompanied by a blue-shift in the emission maximum. These observations are rationalized based on the postulate that the backbone conformation of the conjugated polymer is modulated upon interaction of the surfactant molecules with the polyelectrolytic tethers, which in turn results in a significant depletion of intra-chain interchromophore interactions that are known to cause red-shifted emission bands with significantly lower emission yields.     

Extraction chromatographic method for the separation of actinides and lanthanides using EDHBA grafted AXAD-16 polymer

A new extraction chromatographic method has been developed by grafting chloromethylated polymer support with 4-ethoxy-N,N-dihexylbutanamide (EDHBA), for the selective extraction of U(VI), Th(IV), La(III) and Nd(III) from highly acidic matrices. The developed grafted polymer has been characterized using ¹³C-CPMAS NMR spectroscopy, FT-NIR spectroscopy and also by CHN elemental analysis. The water regaining capacity of the grafted polymer is studied by TGA measurements and the active participation of the amide moiety towards metal ion complexation has been confirmed by Far IR spectroscopy. For the quantitative extraction of metal ions to the resin phase, various physio-chemical parameters are optimized by both static and dynamic methods. The developed amide grafted polymeric matrix shows good distribution ratio values even at high acidities, with the maximum metal sorption capacity values being 0.36, 0.69, 0.32 and 0.42 mmol g⁻¹ for U(VI), Th(IV), La(III) and Nd(III), respectively, at 6 M HNO₃ medium. The kinetics of metal ion phase equilibration is found to be moderately fast, with t_1/2 values of <6 min, for all the analytes of interest. The limits of analyte quantification (LOQ) using the developed method are in the range of 15-30 μg L⁻¹. Moreover, the sequential separation of the sorbed actinides and lanthanides could be achieved by first eluting with 100 mL of distilled water (for actinides) followed by elution with 20 mL of 0.1 M EDTA (for lanthanides). The selectivity behavior and the practical applicability of the developed resin are tested using synthetic low level nuclear reprocessing mixtures and also with monazite sand. The analytical data are within 3.8% relative standard deviation, reflecting the reproducibility and reliability of the developed method.     

Synthesis and structure of the grafted layer on silicas chemically modified by aminophosphonic acids

The synthesis and properties of three representatives of a new class of chemically modified silicas containing aminophosphonic acids, namely, (N-methyl-N-propylamino)methylenephosphonic,N-propylaminodi(methylenephosphonic), andN-[2-(propylamino)ethyl]-N,N-di(methylenephosphonic acids), covalently grafted on the silica surface are reported. The modified silicas were obtained by the two-step Kabachnik-Fields reaction in high yields. The concentrations of the grafted groups were determined by elemental analysis and pH-titration. The new materials were characterized by IR and³¹P and¹³C high resolution solid state NMR spectroscopy. The hydration of the modified silicas was found to result in a significant change in the structure of the grafted layer and to increase the mobility of the grafted groups. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2340–2345, December, 1999.     

Stability of Colloidal Silica Modified by Macromolecular Polyacrylic Acid (PAA) – Application of Turbidymetry Method

The effect of anionic polyacrlic acid (PAA) adsorption on fumed silica (SiO₂) surface on suspension stability was studied. The turbidymetry method was applied to monitor the changes in the suspension stability (using apparatus Turbiscan Lab^Expert with cooling module TLAb Cooler). PAA macromolecules contain dissociable carboxyl groups, therefore, all measurements were carried out at three pH values: 3, 6 and 9. Analysis of obtained transmission and backscattering curves and Turbiscan Stability Indexes (TSI) allowed determination of the most probable mechanism of the stability of the studied systems. The PAA adsorption has the greatest impact on the silica suspension stability at pH 3 (significant improvement of its stability). On the other hand, the presence of polyacrylic acid at pH 6 causes a noticeable deterioration of system stability conditions. At pH 9, polymer minimally influences the stability of SiO₂ suspension.     

Collapse‐expansion transition of elastic shell induced by grafted polymer chains

A coarse‐grained model for an elastic shell grafted with polymer chains is investigated by molecular dynamics methods. With increasing the number of grafted polymer chains (GPCs), it is found that the conformation of the shell undergoes from expansion to collapse and back to the expansion. By varying the density of the GPCs, the phase transition of the elastic shell can be successfully controlled at moderate bending energy of the shell and at moderate binding energy between the shell and GPCs. Furthermore, the self‐assembly structures of the GPCs are also affected by the elastic shell in certain conditions. In the case of a few GPCs on the shell, the chains tend to be adsorbed on the shell surface unfolded at high value of bending energy. However, when the bending energy is small, the chains can be folded several times easily. This may be an important step toward a deeper understanding of how to control the microstructure in the production of biocomposites. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis of microspheres stabilized sterically with two-component grafted chains by dispersion copolymerizations using mixture of two macromonomers in nonaqueous media

The polymer microspheres were synthesized by dispersion copolymerization of divinylbenzene (DVB) with two vinylbenzyl-terminated poly(ethylene glycol methylether) (PEG)/poly(t-butyl methacrylate) (PBMA) macromonomer blends in methanol. In these systems of two macromonomer blends as the emulsifier, the polymer microspheres formed had a very narrow particle size distribution. Two macromonomers formed comicelles with DVB monomer and acted not only as the comonomer but also as the stabilizer. Such polymer microspheres were stabilized sterically with two-component grafted chains, such as PEG and PBMA, in methanol.     

On the collision efficiency in polymer flocculation of colloidal particles

The applicability of the conventional collision efficiency approach for the case where the collision of colloidal particles is not necessary for the rate-determining step is examined. On the basis of a dynamical treatment, we show that the fundamental assumption made in the conventional analysis may lead to a significant error. Depending upon the ratio of the number of sites on the colloidal surfaces to the number of polymer molecules, and the relative magnitudes of the desorption rate constant and the adsorption rate constant, the collision efficiency calculated by the conventional analysis may be either underestimated or overestimated. The present approach yields the temporal variation of the distribution of the fractional surface coverage. It can be shown that if the number of colloidal particles is large, using the mean fractional surface coverage instead of the exact distribution of the fractional surface coverage is sufficient for the evaluation of the collision efficiency.     

The effect of environmental conditions on the steric stabilization of casein micelles

In an attempt to characterize the steric stabilizing sheath around the casein micelles of bovine milk, photon correlation spectroscopy techniques have been used to measure the micellar radius on exposure to ethanolic buffers of varying pH, ionic strength and calcium concentration. It is shown that on exposure to alcohol, the stabilizing protein sheath undergoes dimensional collapse and that immediately prior to aggregation, a minimum or core radius is reached, characteristic of the diluting buffer conditions. Defining barrier thickness as the difference between the micellar radius in alcohol-free buffer and this minimum radius, the same linear relationship is observed between barrier thickness and the critical ethanol concentration required to reach the core radius and induce subsequent aggregation, whether those variations in barrier thickness were achieved by altering the pH, ionic strength or calcium level of the buffer. Considering the initial rate of response to added ethanol as a measure of barrier strength, it is observed that thicker barriers are weaker whereas thinner barriers are more resistant to collapse and hence intrinsically stronger. This paradox is qualitatively resolved by considering the stabilizing sheath to possess some of the characteristics of a weak or soft gel, whose rigidity or extent of cross-linking is influenced by the variations in buffer conditions.     

The effects of cis–trans configuration of cyclohexane multi-carboxylic acids on colloidal forces in dispersions: steric, hydrophobic and bridging

The effects of cis- and trans-1,2-, trans-1,4-cyclohexanedicarboxylic acid, 95% cis-1,3,5-cyclohexane tricarboxylic acid and cis-1,2,3,4,5,6-cyclohexanehexacarboxylic acid on the yield stress–pH behaviour of concentrated ZrO₂ dispersions are reported. Adsorbed cis-1,2,3,4,5,6-cyclohexanehexacarboxylic acid imparts predominantly steric interactions. It forms a steric barrier keeping the interacting particles apart. Adsorbed cis- and trans-1,2 increase the maximum yield stress and this was attributed to a hydrophobic force resulting from the part of the cyclohexane ring sticking out into the solution which is devoid of charged or hydrophilic group. Adsorbed trans-1,4 increases the maximum yield stress by at least threefold and its configuration favours strong bridging interaction with an adjacent particle. Predominantly, cis-1,3,5 also increases the maximum yield stress but only by 60% at the same additive concentration. This was attributed to a smaller degree of bridging.     

Control of thermal,mechanical, and optical properties of three‐component maleimide copolymers by steric bulkiness and hydrogen bonding

N‐substituted maleimides polymerize in the presence of a radical initiator to give polymers with excellent thermal stabilities and transparency. In this study, we synthesized various maleimide copolymers with styrenes and acrylic monomers to control their thermal and mechanical properties by the introduction of bulky substituents and intermolecular hydrogen bonding. Three‐component copolymers of N‐(2‐ethylhexyl)maleimide in combination with styrene, α‐methylstyrene (MSt), or 1‐methylenebenzocyclopentane (BC5) as the styrene derivatives, and n‐butyl acrylate, 2‐hydroxyethyl acrylate, 4‐hydroxybutyl acrylate, or acrylic acid as the acrylic monomers were prepared by radical copolymerization. These copolymers were revealed to exhibit excellent heat resistance by thermogravimetric analysis. Glass transition temperatures increased by the introduction of bulky MSt and BC5 repeating units. The mechanical properties of the copolymer films were improved by the introduction of intermolecular hydrogen bonding. Optical properties, such as transmittance, refractive index, Abbe number, and birefringence, were determined for the copolymers. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1569–1579     

Long‐term stability of an ambient self‐curable latex based on colloidal dispersions in water of two reactive polymers

An ambient self‐curable latex (ASCL) was prepared via the blending of colloidal dispersions in water of a chloromethylstyrene‐functionalized copolymer and a tertiary‐amine‐functionalized copolymer. Upon casting and drying under ambient conditions, the ASCL could generate crosslinked continuous polymer films. The crosslinking occurred via the Menschutkin reaction (quaternization) between the two types of functional groups. Because this reaction was reversible at high temperatures, the films could be decrosslinked and hence were self‐curable. The prepared ASCL exhibited excellent colloidal and chemical stability during long‐term storage: no significant changes in the colloidal properties, such as the particle size, electrophoretic mobility, and crosslinking reactivity, were observed after 48 months of storage. The electrophoretic measurements indicated that the electrostatic repulsion between the negatively charged particles of the ASCL was responsible for the excellent stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2598–2605, 2005     

Properties of star-branched and linear chains in confined space: a computer simulation study

We studied the properties of simple models of linear and star-branched polymer chains confined in a slit. The polymer chains were built of united atoms and were restricted to a simple cubic lattice. Two macromolecular architectures of the chain linear and star-branched with three branches (of equal length) were studied. The excluded volume was the only potential introduced into the model and thus, the system was athermal. The chains were put between two parallel and impenetrable surfaces. Monte Carlo simulations with a sampling algorithm based on chain’s local changes of conformation were carried out. The differences and similarities in the global size and the structure and of linear and star-branched chains were shown and discussed.