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Attractive interactions between negatively charged bovine serum albumin (BSA) at pH 7 and 9 and poly(sodium acrylate) were obtained by substituting a small fraction of acrylic units with alkylacrylamide units. Using light scattering, equilibrium dialysis, and viscometry, we investigated, in dilute solution, the association between BSA and two sets of modified polyacrylates of mean molecular weight 5000 and 150 000, respectively. The formation of complexes was revealed by pronounced increases of the scattering depending on the hydrophobicity of the synthetic polymer. It was not observed with entirely hydrophilic polyacrylates under the same conditions. In the case of long polyacrylates, the apparent hydrodynamic radius of the complexes was slightly larger than that of the free polymer. The polydispersity in size of the complexes seemed low. In the case of short polyacrylates, the complexation can be depicted as the “adsorption” of several polymer chains per protein. In contrast, complexes with long polyacr...

Stabilization of aqueous dispersions of highly hydrophobic colloidal particleshere three integral membrane proteins of nanometric dimensionswere obtained by substituting the classical protective layer of surfactant with low molecular weight amphiphilic polymers (“amphipols”). These polymers, derived from poly(acrylic acid), adsorb onto the particle despite the presence of residual surfactant from the initial stock solutions of proteins. Unbound amphipols and surfactants can be subsequently removed without dissociation of the complex or precipitation. As a consequence of multipoint attachment between the partners, complexation appears irreversible on the time scale of a few hours to a few days. Protein/amphipol complexes contain a much lower number of alkyl groups per particle as compared with classical protein/surfactant complexes. The density of coverage (≈100−200 alkyl groups per particle) increases with the salt concentration of the medium but is not sensitive to pH.

Derivatives of poly(sodium acrylate) bearing a few mole percent of perfluoroalkyl side chains were synthesized. Their solution properties were investigated by rheology and compared to those of their hydrogenated analogues. As the hydrogenated modified polymers, these new materials display an associating behavior. In semidilute solution the modified polymer exhibits viscosities of several orders of magnitude higher than the unmodified poly(sodium acrylate). However, this viscosifying effect is more pronounced for the perfluorinated derivatives. By comparing the rheological behaviors we find that a polymer bearing C7F15CH2 side groups is as associative as a polymer containing the same fraction of C13H27 chains. This is in agreement with Ravey and Stebe's1 conclusions concerning surfactant association that a CF2 is equivalent to 1.7CH2 as regards its hydrophobicity. Mixtures of the perfluorinated polymers with their hydrogenated analogues or with hydrogenated surfactants were successively studied. For low mo...

Provided the molecular weight of the polymer is high enough (10 6 or higher), near-equilibrium bridging flocculation of silica sphere suspensions by poly(ethylene oxide) (PEO) can be observed at high pH (8 or above) and low ionic strength (10 −2 M or below). A diphasic zone, limited by a closed loop, is observed. Its boundaries are highly dependent on several parameters such as the pH, ionic strength and size of the particles. Various and often unusual rheological behaviour is encountered across the different domains of the phase diagram. This behavior is closely related to the degree of polymer adsorption and the polymer to particle size ratio.

Des derives hydrophobes du polyacrylate de sodium (HMPA) portant des greffons alkyles perfluores ont ete synthetises. Leur comportement en solution aqueuse a ete etudie et compare a celui de derives analogues portant des chainons lateraux hydrogenes. Comme escompte, les derives perfluores ont une plus forte tendance a s'auto-associer que les derives protones. Un polymere portant des groupements lateraux -CH 2 C 7 F 15 et un derive portant le meme nombre de groupements - C 13 H 27 ont des proprietes rheologiques similaires. Nous concluons ainsi qu'un CF 2 est equivalent a 1,7 CH 2 du point de vue de l'hydrophobie. Ravay et Stebe 1 ont obtenu une relation similaire en comparant des tensioactifs fluores et protones. En solution semi-diluee, l'agregation des chaines laterales hydrophobes a une tres grande influence sur la rheologie du systeme : les HMPA presentent des viscosites de plusieurs ordres de grandeur superieures a celle du PA non modifie. La correlation entre l'augmentation de viscosite et l'association hydrophobe a ete confirmee par diffusion des rayons X aux petits angles pour les derives fluores et par spectroscopie de fluorescence pour les hydrogenes.

The association of a series of hydrophobically modified poly(sodium acrylate) (HMPA) with lysozyme, a cationic globular protein, or with bovine serum albumin (BSA), an anionic globular protein, was investigated at pH=9 by rheology and to a lesser extent by steady-state fluorescence spectroscopy. Under suitable concentration conditions, this association leads to a drastic viscosity enhancement which is improved when the polymer hydrophobicity is increased. A mechanism is proposed: the hydrophobic regions of the globular proteins interact strongly with the alkyl groups of one or more polymer chains. In the later case, the macromolecules are crosslinked via the proteins, which leads to viscosity enhancement and even gelation. Analogies and differences between these systems and surfactant/HMPA systems previously studied in our laboratory are emphasized and discussed.

Adsorption and flocculation properties have been investigated for a well-characterized aqueous system of precipitated nanometric silicabeads in the presence of a high molecular-weight poly(ethylene oxide). Particular attention was given to the evolution of these properties with increasing concentration. In addition, the corresponding consequences on the rheological behavior in the homogeneous domains of the phase diagram of the systems were studied. Important rheological effects can actually be obtained with such systems, even at moderate values of the volume fraction of the dispersed phase (5·10−3≦Φ≦5·10−2). According to the adsorption level, the number of particles per macromolecular chain, and the free polymer equilibrium concentration, quite different phenomena were observed such as rheopectic shear-induced gelation, Newtonian flow or thixotropic shear-thinning.

The formation of polymer complexes was studied between poly(ethylene oxide) (PEO) and poly(N-vinylpyrrolidone) (PVP), as hydrogen-bond acceptors and copolymers of acrylic acid (AA) with vinylsulfonic acid (VS) or with 2-acrylamido-2-methylpropanesulfonic acid (AMPS) as hydrogen-bond donors. Under acidic conditions (e.g., pH≃3), the strong-acid groups (VS or AMPS) are dissociated and uncomplexable, while the carboxylic groups (COOH) can be complexed by the polybase (PEO or PVP). Potentiometric and viscometric studies showed that the properties and the structure of the complexes formed depend on the experimental parameters: molar content of sulfonated monomers, concentration of polyacid and polybase, molecular weight of polymers, and nature of polybase

Adsorption of various cationic copolymers onto clay and silica particles is investigated through microcalorimetry. On the homogeneous clay surface, the fraction p of adsorbed segments in a homopolyelectrolyte chain is calculated from comparison of the enthalpy of displacement, ΔH , of the polymer molecule with that of the monomer unit. The results are consistent with a frozen-in configuration of the macromolecules at the interface, due to the high adsorption energy of the cationic unit (4 kT). When the ionic content of the chain is decreased, the value of ΔH becomes smaller and smaller and is no longer measurable for nonionic polymers. Considering the evolution of ΔH during monomer adsorption, the silica surface appears heterogeneous. However, the ΔH values observed for the most charged polymers are again constant because only the most reactive surface sites are engaged in the polymer adsorption.

Cette mise au point resume les travaux effectues par les laboratoires membres de l'Action de Recherches Coordonnees "Floculation par les Polymeres Hydrosolubles" qui ont porte sur la floculation de colloides modeles, silices ou latex, par des polymeres hydrosolubles, le plus souvent de la famille des Polyacrylamides. On a determine les parametres pertinents relatifs a l'adsorption des polymeres sur les surfaces des colloides, aux quantites de polymeres permettant d'obtenir une floculation optimale (minimum de turbidite de la phase surnageante), et a la cinetique de floculation. Ces parametres regissent la contribution relative des deux mecanismes principaux de floculation, par neutralisation des charges et par pontage interparticulaire. La structure des agregats (ou flocs) peut, dans des cas favorables, etre observee directement par microscopie electronique apres congelation rapide. Elle peut aussi etre analysee par diffusion de neutrons aux petits angles, et assez bien interpretee lorsque l'on se trouve dans des situations pas trop eloignees des conditions d'equilibre. Les modeles d'agregation ont ete egalement utilises pour analyser la compacite des amas, traduite en termes quantitatifs par leurs dimensions fractales. Les modeles pertinents, pour chaque situation, peuvent etre selectionnes grâce a l'analyse de la distribution des tailles de flocs. Dans cette optique, l'introduction des polymeres dans les modeles d'agregation n'est pas absolument obligatoire.

The rheological behavior of mixtures containing hydrophobically modified poly(sodium acrylate) (HMPAA) and surfactants is studied. The hydrophobic groups of the polymer (octadecyl or dodecyl chains) interact with the surfactant molecules to form mixed micellar-type aggregates. In semidilute solution these mixed aggregates act as cross-linkers between the polymer chains, inducing a viscosification or gelation of the system. The strongest effect was observed with a cationic surfactant, because in this case both electrostatic attraction and hydrophobic interactions contribute to the stabilization of the mixed aggregate. However, association occurs even between HMPAA and an anionic surfactant (SDS), despite the unfavorable electrostatic repulsions, indicating that the hydrophobic interactions are the driving force for the formation of the mixed aggregates.

The behavior of dilute clay colloids/cationic copolymers systems is investigated as a function of the ionic strength I of the medium for various charge levels of the polyelectrolyte chain. Changing I not only has an inflauence on the interaction between the surface and the electrostatically bound segments but can also more or less affect the copolymer conformation according to its ionicity degree. The dependence of adsorption and flocculation processes on the ionic strength can be explained through these both effects.

The aggregation in aqueous solution of a hydrophobically modified polyelectrolyte was investigated by 19 F n.m.r. The polymer studied was a poly(sodium acrylate) of average molecular weight 5000 bearing 8 mol% of −CH 2 C 7 F 15 pendant alkyl chains. The 19 F n.m.r. spectra of the modified polymer displayed the characteristic features of slow exchange between the free and the aggregated states for the alkyl chains. It is therefore possible to determine the respective fractions of free and aggregated −CH 2 C 7 F 15 groups by direct integration of the n.m.r. signals. This behaviour is opposite to the fast exchange occurring for classical surfacants (sodium pentadecafluorooctanoate, SOF). The exchange process in the polymer case is at least three orders of magnitude slower than in the surfactant system.

What do the following have in common: fog, water-based paints, milk and mayonnaise? They are all colloidal states. It was the British physicist Thomas Graham who, in 1861, invented the generic term ‘colloid’ from the Greek word kolla for glue. He intended thereby to highlight a characteristic which he attributed to a whole class of special chemical products. At the time, Graham was studying the diffusion properties of various substances in solution, and hoped to distinguish those capable of going through a wall of parchment from those which were not. Whereas the former invariably exhibited a crystalline form in the pure state (he used sugars and mineral salts), those that could not penetrate the wall, such as albumen and gelatin, had a rather glutinous appearance which, in his view, was specific to them. His proposed classification of chemical substances into two main categories, the ‘crystalloids’ and the ‘colloids’, was based upon these diffusion criteria.

Studies of the adsorption of high molecular weight polymers on colloidal latex and silica particles and their subsequent flocculation were carried out. Neutral polyethylene oxide samples with both a narrow and a broad molecular weight distribution were used together with low charged cationic copolymers. The influence of the particle concentration and polymer dose on the flocculation were systematically investigated under quiescent conditions. Equilibrium bridging only occurred with polyelectrolyte, even in very dilute suspensions, at high particle coverage. In contrast to this, non-equilibrium bridging occurred with both neutral polymer and polyelectrolytes but only for more concentrated suspensions and small amounts of adsorbed polymer. Polymer adsorption in dilute suspensions, which did not show particle aggregation was measured an electrophoretic technique. In more concentrated suspensions, where flocculation takes place, we found that aggregation prevents further polymer adsorption and induces both an excluded volume and a surface effect. The consequences on the shape of the isotherms differ according to the aggregation mechanism. A significant decrease of the amount, Γ, of adsorbed polymer is observed with non-equilibrium bridging. When both mechanisms simultaneously contribute to the aggregation, the value of Γ depends on their relative importance. In the intermediate range of copolymer dose their respective contributions are critically sensitive to the details of the mixing step and stirring, leading to non reproducible experimental results.

Viscometry and fluorescence spectroscopy are used to study the dilute solution behavior of hydrophobically modified polyelectrolytes. Random copolymers of sodium acrylate and alkylacrylamide are used for this study. The alkylacrylamide content is low, 1–3 mol%, and the length of the alkyl group ranges from octyl to octadecyl. Upon addition of NaCl these copolymers exhibit a transition from a nonaggregated coil to an aggregated one. The transition occurs above a critical salt concentration which is dependent on the length and the content of alkyl groups. This behavior is ascribed to the formation of intrachain hydrophobic aggregates. The copolymer with the shortest alkyl chain (octyl) does not exhibit such aggregation at least in the range of salt concentrations studied, i.e. ≤ 15% NaCl.

Depending on experimental conditions, adsorbed polymer layers on particles can either increase or decrease the stability of a collidal dispersion. The aggregated formed in the latter case are called flocs. Numerous macroscopic techniques are used to clear up the factors that control their formation and it appears that flocculation of suspensions by addition of macromolecules proceeds via various mechanisms form bridging to charge neutralization according to the kind of the polymer‐particle interaction. The organization of the particles inside the aggregates is examined by small angle neutron scattering (SANS). It is mainly governed by the remaining interparticle repulsions. Different structures can be observed when these repulsions decrease: linear necklaces branched clusters, tridimensional aggregates with short range liquid like order and finally fractal objects when the surfaces can be brought to contact.

A chiral polymer easily obtained by treatment of a linear polyacrylamide with l -proline was adsorbed on a silica support treatment of a linear polyacrylamide with l -proline. After complexation with copper(II), and in spite of a rather low efficiency due to slow ligand exchange, such packings are very convenient for the resolution of amino acid enantiomers eluted in water (relative retentions, k ′ L / k ′ D , higher than 2 may be observed). Other eluents may also be used. The chiral polymer was studied in solution by potentiometry and nuclear magnetic resonance spectroscopy ( 13 C relaxation measurements). A model of the complex involved in the stereoselection is proposed which accounts for the chromatographic results obtained.

Resume Les methodes statistiques ont permis l'etude theorique de la cinetique de degradation thermique de polycondensats reticules. Les parametres introduits dans les calculs sont le degre de reticulation, la masse moleculaire des monomeres et le degre d'avancement de la reaction de synthese du polycondensat. L'accord est satisfaisant entre resultats theoriques et donnees experimentales obtenues par thermogravimetrie isotherme de macromolecules modeles contenant des noyaux s-triaziniques.

Chloride ion activity coefficients in aqueous solutions of several cationic copolymers have been determined using ion-selective electrodes in both the absence and the presence of simple univalent and divalent salts. Without added salt, the activity coefficient depends on the polymer concentration. It increases with increasing concentration of the added salt. The extent of interaction between counterions and polyions at a given polymer concentration, as estimated form chloride anion activity, is greater for bivalent than for univalent anions. Experimental data are in good agreement with theory. Selective interaction of anions with the ammonium copolymers has also been evidenced by viscometry. The selectivity follows the order For organic anions, in addition to electrostatic interactions, hydrophobic effects, which depend on the structure of the copolymer, play a significant role.

On the basis of the expected mechanism of chiral recognition in ligand exchange chromatography, a new chiral packing was prepared and tested. The optically active phase is a copolymer of acrylamide and of a vinylpyridine monomer substituted by anL-pro-line moiety. The packing is obtained by simple coating of a chro-matographic silica followed by a convenient complexation with cupric ions. The selectivity factor, α, for such a packing is high : it is between 2 and 8 for most amino acids.

Resume La degradation thermique du polybutanamide (polyamide-4) a eteetudiee par analyse thermique differentielle et par thermogravimetrie. Les influences de residus du catalyseur de polymerisation, de la nature des groupements terminaux et des oligomeres presents dans l'echantillon sur la vitesse de degradation, ont ete demontrees. La comparaison des thermogrammes realises d'une part sous vide et d'autre part sous balayage d'azote nous a conduit a admettre la formation d'oligomeres cycliques au cours de la degradation. En considerant des reactions de depolymerisation, de coupure au hasard de la chaine macromoleculaire et de formation d'oligomeres cycliques, nous avons pu indiquer le role que jouent les groupements terminaux (meme ceux formes par un traitement dit de stabilisation) des chaines macromoleculaires dans les reactions de degradation.

Samples of starch-g-polyacrylonitrile were prepared using the Ce4+ion as initiator. We discuss the influence of the origin of the starch on the polyacrylonitrile content of the copolymer, on the frequency of the grafted chains, and on the molecular weight of the graft. Relations between alkaline hydrolysis conditions and liquid absorption were also studied. The retention increases with the molecular weight of the grafted polyacrylonitrile, and this factor depends on the origin of the starch. Higher absorptions were obtained with low amylose content samples. An absorption maximum was observed that depends on the time of hydrolysis and consequently on the carboxylate group content.

Polyacids form polymer complexes with polybases (proton acceptors) through hydrogen bonds. This result is well-known for homopolymer/homopolymer mixtures but only a few studies have been devoted to homopolymer/copolymer pairs because of the complexity of such systems. In this study a very simple model is proposed to take into account the influence of uncomplexable groups in the copolymer chain on complex formation. Several polybases (polyoxyethylene, polyvinylmethylether, polyvinylpyrrolidone) are used as homopolymers, and partially neutralized poly(acrylic acid) as copolymer; the acrylate groups are uncomplexable and behave as structure defects. It was found that the degree of complexation increases continuously with the concentration ratio [polybase]/[polyacid]. There is an exponential relation between the degree of complexation and the number of structural defects on the copolymer chain.

Soluble and insoluble polymeric Schiff bases PolySalPn and PolySal-DPT* have been synthesised. The polymers and their copper(II), nickel(II) and cobalt(II) complexes have been fully characterised by their elemental analyses and by spectroscopic methods. The Co—PolySalDPT proved to be as efficient as the corresponding monomeric complex in catalysing the oxidation of 2,6-di-t-butylphenol.

In order to explain the separation mechanism of α-amino acid enantiomers by ligand exchange chromatography on chiral, metal complexed stationary phases, soluble models of this packing have been prepared by reaction of isobutyramide and polyacrylamide with L-proline. Metallic ternary complexes of these ligands with L or D-valine or proline have been investigated through potentiometry and NMR spectroscopy. The results allows us to propose the coordination complex structures involved in the stereoselection.

Resume Des echantillons d'acide polyacrylique et polymethacrylique, soigneusement purifies, ont ete pyrolyses en atmosphere non oxydante entre 160 et 240°. Le comportement thermique de ces polymeres a ete etudie par thermogravimetrie, par spectroscopie infra-rouge, par dosage protometrique du pyrolysat et surtout par une methode chromatographique qui permet d'analyser les produits de decomposition et de preciser simultanement leur cinetique de formation. Dans les deux cas, l'examen des cinetiques de formation des produits volatils de pyrolyse montre qu'il y a competition entre une reaction de deshydratation et une reaction de decarboxylation. Les deux reactions ne sont pas independantes. La deshydratation est la reaction principale et meme presque exclusive pour l'acide polymethacrylique, mais son importance decroit quand la temperature augmente. La formation de faibles quantites de monomere a ete notee dans le cas de l'acide polymethacrylique.

Resume Il existe de nombreuses methodes de determination de l'energie d'activation de la pyrolyse des polymeres effectuee par thermogravimetrie dynamique. Toutefois, la plupart d'entre elles conduisent a des resultats qui dependent sensiblement du mode de degradation de la macromolecule. Seules celles qui mettent a profit l'evolution des thermogrammes avec la vitesse de chauffage sont des methodes absolues, c'est a-dire independantes du mecanisme de pyrolyse. Ces methodes absolues sont ici etudiees et comparees d'un point de vue theorique et experimental, en ce qui concerne leur precision, leur rapidite et leur simplicite de mise en oeuvre. Cette analyse montre que les methodes integrales sont preferables a la methode differentielle.

Friedel—Crafts crosslinking of polystyrene has been performed with 9,10-dichloromethylanthracene (A(MC)2) in 1,2-dichloroethane solution. The extent of the reaction is followed by UV spectroscopy. The number of crosslinks is a strongly non-linear function of the reaction time. We found that the variation of properties of the sol molecule distribution such as weight, average molecular weight and average radius of gyration and the viscosity near the gel point depend on kinetics. We performed a computer simulation of the kinetics of the reaction which may explain this observation.

We study the formation of weak reversible gels of galactomannans induced by borate complexation. Phase diagrams observed in water and in 1M NaCl are presented. To obtain information about the crosslinking mechanism involved in the gel formation, interactions of galactomannan and glycoside models with borate are studied by 11B-NMR. Evidence of the existence of five-member ed and six-member ed ring mono-and di-complexes is given. The corresponding complexation constants and peak assignments are reported. The mono-complexation constant, K1, has been determined for guaran in 1M NaCl from dialysis experiments: K1 = 11·4 litres mol-1. This value is close to those reported for glycoside models.

Measurements were conducted on the linear viscoelastic properties of hydrophobically modified poly(sodium acrylate) reversibly cross-linked with proteins to form gels. The native structure of proteins was not markedly affected upon association with the amphiphilic polyelectrolyte. Hydrophobic interaction was shown to overcome Coulombic effects on interpolymer complexation. Because of their relative hydrophobicity, neutral papain and positively charged lysozyme were found to be less efficient cross-linking agents than negatively charged bovine serum albumin. These reversible gels exhibited similarities with chemically cross-linked macromolecules such as a plateau modulus at high frequency and characteristic scaling at the transition point between sol and gel. The sol−gel transition diagrams were determined. A semiquantitative approach, based on scaling laws, was able to capture the essential rheological properties of these mixtures, namely sol−gel transition and variations of storage modulus.