Françoise Candau

Synthesis and characterization of polystyrene-poly(ethylene oxide) graft copolymers

Abstract Amphiphilic graft copolymers have been synthesized. The grafting reaction proceeds by anionic deactivation of a ‘living’ monofunctional poly(ethylene oxide) onto a partly chloromethylated polystyrene backbone. The copolymers are well-defined compounds (molecular weight of the backbone, number and length of the grafts are known), which exhibit narrow molecular weight distribution and are shown to be homogeneous in composition. The degree of grafting is high. Light scattering, vapour pressure osmometry, ultra-violet spectroscopy, nuclear magnetic resonance, differential refractometry and gel permeation chromatography were used for an accurate characterization of the structure of these copolymers.

Effect of molecular weight on the refractive index increment of polystyrenes in solution

Abstract The variation of refractive index increment d n d c with molecular weight has been studied using solutions of monodisperse polystyrenes (2000 We have shown that the linear relationship: d n d c = d n d c m + K″ Mn where ( d n d c) m is the refractive index increment of the repeating unit and K″ a constant, holds only for low molecular weights. With the assumption of volume additivity, we have estimated quantitatively the linear portion of the curve, d n d c =f( 1 M ) , observed for molecular weights below 20 000 as a function of polymer composition. Beyond this limit, the increase of d n d c with molecular weight may be probably related to segment-segment interactions within the coil.

Effect of molecular weight on the partial specific volume of polystyrenes in solution

Abstract The partial specific volume v 2 of linear and branched polystyrenes has been measured as a function of molecular weight (1300 about 20 000), we have detected small but significant variations due to the intramolecular segment-segment contacts within the coil. We have proposed an empirical relation between v 2 and the segment density of the macromolecule; this relation has been confirmed using highly branched polystyrenes. These results relative to dissolved polystyrenes are compared to experimental data obtained by different authors on pure liquid polystyrenes at different temperatures. Starting from simple additivity rules and from the known chemical composition of liquid polymers, we have shown that the variation of specific volume with high molecular weights is due to some phenomenon different from an effect of chain-ends.

Structure of colloidal particles in water oil mixtures stabilized by polymeric emulsifiers: 1. Phase diagrams and electron microscope studies

Abstract The phase diagrams of toluene/water mixtures, stabilized by amphiphilic graft copolymers in the presence of an alcohol, show two domains in which these systems are optically clear. The composition of the continuous phase of the polymeric microemulsions was determined by dialysis experiments. The results indicate a preferential solvation of the copolymer sequences by the ternary solvent mixture. The micellar particles were observed by electron microscopy on carbon replicas of freeze-fractured samples. Depending on the copolymer composition and the location of the system in the phase diagram, the micrographs reveal either individual particles ( 50 A radius A ), well-dispersed in the continuous medium, or inter-particle clusters.

Structural properties and topological defects of swollen polymeric mesophases: Low angle X-ray diffraction and optical microscopic studies

Abstract Homogeneous mesophases encountered in water-toluene mixtures stabilized by polystyrene-poly(ethylene oxide) graft copolymers in the presence of 2-propanol are investigated. In these four-component systems, mesomorphic phases are produced for fairly high values of the copolymer/2-propanol ratio close to the transition region between cloudy and transparent systems. Low angle Xray diffraction studies show evidence of lamellar and reversed hexagonal structures, according to the composition of the systems. By addition of 2-propanol, the birefringent phases undergo a transition to isotropic systems which have either a cubic structure or consist of reversed water-swollen micelles. The existence of mesomorphic phases was further confirmed by optical microscopic investigation. These dilute polymeric mesophases exhibit a great variety of textures similar to those encountered in low molecular-weight lyotropic systems (soaps). For lamellar structures, typical textures such as classical focal conics, oily streaks, or batonnets are described and discussed. In addition, well-resolved polygonal arrays, interpreted recently in terms of a parabolic focal conic structure by Rosenblatt et al. , are also observed. The textures most commonly found for hexagonal structures include fan-shaped and striated ones. These observations have been complemented by flow birefringence measurements.

Etude des volumes specifiques partiels de polystyrenes-modeles—Influence de la masse moleculaire et de la nature des groupements terminaux

Resume Il est generalement admis que le volume specifique partiel η2 des polymeres varie lineairement avec linverse de la masse moleculaire moyenne en nombre M n : η 2 = η m + K/ M n ou ηm represente le volume specifique partiel du polymere de masse infinie et K est une constante. Nous avons verifie, en utilisant des serie homologues de polystyrenes-modele comportant des extremites de chaines differentes, que cette loi lineaire est suivie quel que soit le solvant, tant que la masse moleculaire est inferieure a 4·104. Les valeurs du coefficient K, et ses variations avec la nature des groupements terminaux et du solvant, peuvent etre prevues grâce a un modele de calcul simple que nous proposons. Nous montrons, en outre, que ηm nest pas le volume specifique du polymere de masse infinie: en effet, au dela dune masse de 4·104, la variation du volume specifique avec 1/M nest pas lineaire et nous mettons en evidence une decroissance rapide de η2 quand la masse moleculaire du polymere augmente.

Structure of colloidal particles in water-oil mixtures stabilized by polymeric emulsifiers: 2. Small angle neutron scattering investigation

Abstract Small-angle neutron coherent scattering techniques have been used to characterize the conformation of amphiphilic macromolecules in polymeric microemulsions. The radius of gyration, the molecular weight and the aggregation number of the macromolecules within the micelles have been measured using a dilution procedure in conjunction with an adjustment of the contrast factor between polymer and solvents. Additional information on the internal structure of the micelles has been obtained from the asymptotic behaviour of the scattering form factor P ( q ). From considerations of the respective affinities between the two copolymer sequences and the solvent mixture, plausible models are proposed for the micellar structure.

The effect of temperature and alcohol on the solubilization of water in nonaoueous solutions of polymeric emulsifiers

SummarySolubilization of water in nonaqueous solutions of polymeric surfactants (polystyrene-polyethyleneoxide graft copolymers) has been investigated. The effect of temperature on the formation of single-phase systems reveals the existence of an optimum solubilization temperature which depends on the hydrophilic character of the surfactant. Addition of an alcohol causes an increase in the solubilizing power of the amphiphilic copolymer. Dialysis experiments show that the one-phase homogeneous systems consists of reverse micelles with water solubilized in the interior of aggregates. The type of dispersions obtained in the diphasic region of the phase diagram is studied by N.m.r. experiments. From the results, it appears that the general features of these high molecular weight systems resemble that of classical microemulsions prepared with small nonionic detergents.ZusammenfassungWir untersuchten die Löslichkeit von Wasser in nichtwäßrigen Lösungen von Polymertensiden (Polystyrol-Polyäthylenoxid Pfropfcopolymere). Der Temperatureffekt auf die Bildung von Monophasensystemen ergibt eine optimale Solubilisierungstemperatur, die vom hydrophilen Charakter der Tenside abhängig ist. Fügt man einen Alkohol hinzu, so steigt die Solubilisierungskraft des amphiphilen Copolymerisates. Dialysierungsexperimente zeigen, daß die homogenen Monophasensysteme aus inversen Mizellen bestehen, die Wasser in der Mitte der Aggregate gelöst haben. Solche Dispersionstypen bestehen in der Zweiphasengegend des Phasendiagramms und wurden durch N.m.r.-Experimente bestätigt. Wir zeigten, daß das Verhalten dieser hochmolekularen Systeme gleich denen von klassischen Mikroemulsionen aus kleinen nicht-ionischen Tensiden ist.

Etude morphologique en solution diluee de polystyrenes-modele a structure en peigne

Resume Letude morphologique de polystyrenes en peigne formant des series homologues, a linterieur desquelles lespacement moyen ƒ le long de la chaine est different pour chaque echantillon a ete effectuee par diffusion de la lumiere en milieu cyclohexane et en solution benzenique. Les resultats experimentaux confirment et precisent labaissement de la temperature θ par rapport a celle des polystyrenes lineaires. Dautre part, les dimensions non perturbees de nos echantillons sont inferieures a celles dhomologues lineaires de meme masse et dautant plus importantes que les greffons sont longs et nombreux. Le nombre de greffons portes par le squelette des polystyrenes en peigne determine leur expansion au voisinage du point θ, alors que leur longueur ne semble pas intervenir. Les phenomenes observes peuvent etre en partie expliques par la forte densite en segments qui regne a linterieur de la macromolecule ramifiee.

Solubilization of Immiscible Liquids Into Mesophases Formed from Amphiphilic Block Copolymers

Abstract Optical microscopy and X-ray diffraction studies reveal the presence of highly swollen mesophases in four-component systems containing amphiphilic triblock copolymers. According to the composition of the system, lamellar phases or hexagonal structures are produced. The polymeric mesophases exhibit textures very similar to those encountered in low molecular weight liquid crystalline phases.