Polyester layered silicate nanohybrids by controlled grafting polymerization

peer reviewedPoly( epsilon-caprolactone) (PCL) layered silicate nanohybrids were synthesized by ring opening polymerization of epsilon-caprolactone according to a well-controlled coordination-insertion mechanism. Montmorillonites were surface-modified by non functional (trimethylhexadecylammonium) and hydroxy functional alkylammonium cations, i.e., (2-hydroxyethyl) dimethylhexadecylammonium. The hydroxy functions available at the clay surface were activated into tin( II or IV) or Al(III) alkoxide initiators for lactone polymerization, thus yielding surface-grafted PCL chains. The surface-grafted PCL chains were recovered by an ionic exchange reaction with lithium chloride and they were analyzed by size exclusion chromatography. The PCL molar mass was measured as a function of the hydroxy content of the clay that was modulated by exchanging the Na cations with mixtures of non-functional and hydroxy functional ammonium cations of different compositions. Nanohybrids were also characterized by small-angle X-ray diffraction, transmission electron microscopy and thermogravimetry. The PCL molar mass and the nanocomposite morphology (i.e., exfoliation and/or intercalation) were readily tuned by the content of the hydroxy groups available at the clay surface. Surface-grafted aluminium trialkoxide species proved highly efficient in initiating polymerization that leads to PCL chains of controlled molar mass and narrow molecular weight distribution with polydispersity indices as low as 1.2

Synthèse et caractérisation de poly(fumarates) encombrés

Doctorat en sciences chimiques -- UCL, 199

Impact of polymer Microstructure on theSelf-Assembly of Amphiphilic Polymers in Aqueous Solutions

International audienc

ToF SIMS depth profiling of linear and cross-linked methacrylate polymers thin films using monoatomic ion sputtering

International audienceOwing to their specific physical properties, polymeric materials are increasingly used in the field of nanotechnologies, for instance for nano-impression, lithography or organic light emitting diodes applications. These properties are largely controlled by polymer structural parameters such as molecular weight, polydispersity or crosslinking density…. It is then desirable to have characterisation technique able to provide structural information at the nanometer scale. Considering its intrinsic properties, Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) appears particularly adapted to this purpose. It is then more and more used to investigate structures and chemical composition of polymers developed for nanotechnologies applications [1]. Specifically, low energy caesium sputtering appeared to be a successful path to depth profiling of polymer, providing a reliable chemical information weakly affected by damages generated by the energetic interactions between ions and the organic samples [2]. In this work, we will examine the ToF SIMS depth profiling, using monoatomic caesium ion beam for sputtering, of methacrylate thin film polymers with diverse structural properties. Two kind of nanometric layers coated on silicon wafers are studied: on one hand several molecular weight poly(methyl methacrylate) (PMMA); on another hand a hydroxy-ethyle (HEMA) / methyl methacrylate (MMA) copolymer cross-linked at different levels. Dual beam depth profiling has been performed on a ToF-SIMS 5 instrument (from IONTOF GmbH). The analysis is performed using a 15kV Bi$_3^+$ beam while the sputtering is performed with a Cs beam, energized between 2 keV and 250 eV. The results of these interactions are examined in terms of sputtering yield Y, which is the volume sputtered by each individual primary ion. The effects of structural parameters of polymers on Y will be then discussed considering polymers properties such as glass transition temperature Tg, especially for linear PMMA whose variations of Y has been measured at different temperature around T$_g$

One-Step Fabrication of pH-Responsive Membranes and Microcapsules through Interfacial H-Bond Polymer Complexation

Biocompatible microencapsulation is of widespread interest for the targeted delivery of active species in fields such as pharmaceuticals, cosmetics and agro-chemistry. Capsules obtained by the self-assembly of polymers at interfaces enable the combination of responsiveness to stimuli, biocompatibility and scaled up production. Here, we present a one-step method to produce in situ membranes at oil-water interfaces, based on the hydrogen bond complexation of polymers between H-bond acceptor and donor in the oil and aqueous phases, respectively. This robust process is realized through different methods, to obtain capsules of various sizes, from the micrometer scale using microfluidics or rotor-stator emulsification up to the centimeter scale using drop dripping. The polymer layer exhibits unique self-healing and pH-responsive properties. The membrane is viscoelastic at pH=3, softens as pH is progressively raised, and eventually dissolves above pH=6 to release the oil phase. This one-step method of preparation paves the way to the production of large quantities of functional capsules

Simple and multiple emulsions stabilized by charged-neutral copolymers

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Formation and stabilization of multiple w/o/w emulsions encapsulating catechin, by mechanical and microfluidic methods using a single pH-sensitive copolymer: Effect of copolymer/drug interaction

International audienceMultiple w/o/w emulsions (MEs) are promising systems for protecting fragile hydrophilic drugs and controlling their release. We explore the capacity of a single pH-sensitive copolymer, PDMS60-b-PDMAEMA50, and salts, to form and stabilize MEs loaded with sucrose or catechin by a one-step mechanical process or a microfluidic method. ME cytotoxicity was evaluated in various conditions of pH. Using the mechanical process, the most stable emulsions were obtained with Miglyol®812 N and isopropyl myristate in a final pH range of 8–12 and [0.3 M−1 M] NaCl concentrations. Conversely, with the microfluidic method, isopropyl myristate at pH 3 without salt was more efficient. Catechin strongly affected the formation of droplets by the mechanical process but did not modify the conditions of stability of MEs obtained by the microfluidic method. The antioxidant power of catechin was preserved in the inner droplets, even in emulsions prepared by the mechanical method at pH 8. An incomplete release of sucrose and catechin from the emulsions was observed and attributed to the interaction of molecules with the copolymer through hydrogen bonding. This study highlights some of the barriers to break to formulate multiple emulsions stabilized by a PDMS-b-PDMAEMA copolymer or other polymers which can form hydrogen bonds interaction with encapsulated drugs

Synthesis, characterization, and modeling of ABC triblock terpolymers: the effect of block sequence

Four equimolar terpolymers comprising ten units from each of the monomers methoxy hexa(ethylene glycol) methacrylate (HEGMA), 2(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) were prepared by group transfer polymerization (GTP), and characterized by gel permeation chromatography (GPC) and proton nuclear magnetic resonance (H-1 NMR) spectroscopy to confirm size homogeneity and composition. These terpolymers were the three block sequence isomers, ABC, BAC and ACB, as well as the statistical isomer. Aqueous solutions of the terpolymers were characterized by dynamic light scattering and turbidimetry to determine the hydrodynamic sizes and cloud points. The results indicated micelle formation in the triblocks, and absence of micellization with the statistical terpolymer. in general, a strong dependence of the hydrodynamic size and cloud point on polymer architecture was observed. Monte Carlo simulations on non-aggregating isomeric terpolymers of similar structure also showed a strong dependence of the radius of gyration on polymer architecture

Can we predict emulsion nature by thermodynamics?

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