Bénédicte Lepoittevin

Vapor barrier properties of polycaprolactone montmorillonite nanocomposites: effect of clay dispersion

Different compositions of poly(e-caprolactone) (PCL) and (organo-modified) montmorillonite were prepared by melt blending or catalyzed ring opening polymerization of e-caprolactone. Microphase composites were obtained by direct melt blending of PCL and sodium montmorillonite (MMT-Na+). Exfoliated nanocomposites were obtained by in situ ring opening polymerization of e-caprolactone with an organo-modified montmorillonite (MMT-(OH)2) by using dibutyltin dimethoxide as an initiator/catalyst. Intercalated nanocomposites were formed either by melt blending with organo-modified montmorillonite or in situ polymerization within sodium montmorillonite. The barrier properties were studied for water vapor and dichloromethane as an organic solvent. The sorption (S) and the zero concentration diffusion coefficient (D0) were evaluated for both vapors. The water sorption increases with increasing the MMT content, particularly for the microcomposites containing the unmodified MMT-Na+. The thermodynamic diffusion parameters, D0, were compared to the value of the parent PCL: both microcomposites and intercalated nanocomposites show diffusion parameters very near to PCL. At variance exfoliated nanocomposites show much lower values, even for small montmorillonite content. In the case of the organic vapor, the value of sorption at low relative pressure is mainly dominated by the amorphous fraction present in the samples, not showing any preferential adsorption on the inorganic component. At high relative pressure the isotherms showed an exponential increase of sorption, due to plasticization of the polyester matrix. The D0 parameters were also compared to those of the unfilled PCL; in this case, both the exfoliated and the intercalated samples showed lower values, due to a more tortuous path for the penetrant molecules.

Polymer/layered silicate nanocomposites by combined intercalative polymerization and melt intercalation: a masterbatch process

Abstract Poly(e-caprolactone) (PCL) and poly(vinyl chloride) (PVC) layered silicate nanocomposites were prepared by combination of intercalative polymerization and melt intercalation. In a first step, high clay content PCL nanocomposites were prepared by in situ polymerization of e-caprolactone intercalated between selected organo-modified silicate layers. The polymerization was catalyzed with dibutyltin dimethoxide in the presence of montmorillonites, the surface of which were previously exchanged with (functionalized) long alkyl chains ammonium cations. Then, these highly filled PCL nanocomposites were added as masterbatches in commercial PCL and PVC by melt blending. The intercalation of PCL chains within the silicate layers by in situ polymerization proved to be very efficient, leading to the formation of intercalated and/or exfoliated structures depending on the organo-clay. These masterbatches were readily dispersed into the molten PCL and PVC matrices yielding intercalated/exfoliated layered silicate nanocomposites which could not be obtained by melt blending the matrix directly with the same organo-modified clays. The formation of nanocomposites was assessed both by X-ray diffraction and transmission electronic microscopy. Interestingly, this so-called ‘masterbatch’ two-step process allowed for preparing PCL nanocomposites even with non-modified natural clay, i.e. sodium montmorillonite, which showed a material stiffness much higher than the corresponding microcomposites recovered by direct melt intercalation. The thermal stability of PCL nanocomposites as a function of clay content was investigated by thermogravimetry (TGA).

Poly(ionic liquid) and macrocyclic polyoxometalate ionic self-assemblies: new water-insoluble and visible light photosensitive catalysts

Several poly(ionic liquid)s (PILs) were synthesized and assembled with a multielectronic-process sustaining polyoxometalate (POM) into new green and water-insoluble nanomaterials (POM@PILs). They are visible light photosensitive, unlike their two components. A synergic effect was highlighted for the first time. POM@PILs achieve complete photodegradation of AO7 in aerobic media. The photocatalysts were recoverable and recyclable.

Layered silicate/polyester nanohybrids by controlled ring-opening polymerization

In this study, layered silicate/aliphatic polyester nanohybrids were synthesized by ring-opening polymerization of e-caprolactone as promoted by the so-called coordination-insertion mechanism. These nanocomposites were formed in presence of montmorillonite surface-modified by ammonium cations bearing hydroxyl group(s), such as bis(2-hydroxyethyl)methyl (hydrogenated tallow alkyl) ammonium. The lactone polymerization could be initiated by all the hydroxyl functions available at the clay surface, after activation into either tin(II) or Al(III) alkoxide active species. Hybrid nanocomposites were accordingly generated through the covalent grafting of every polyester chain onto the filler surface. Surface-grafted polycaprolactone (PCL) chains were untied and isolated by ionic exchange reaction with LiCI in THF solution and molar masses were measured by size exclusion chromatography. The PCL molar masses could be controlled and readily tuned by the content of hydroxyl groups available at the clay surface. Interestingly, initiation reaction by aluminum trialkoxide active species yielded grafted PCL chains characterized by very narrow molecular weight distribution (M w /M n ∼1.2). These polyester-grafted layered silicate nanohybrids displayed complete exfoliation of silicate sheets as shown by X-ray diffraction (XRD) and transmission electron microscopy (TEM).

Surface initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine on poly(ethylene terephthalate)

Poly(ethylene terephthalate) (PET) substrates were modified by means of surface-initiated supplemental activator and reducing agent atom transfer radical polymerization (SI-SARA-ATRP) of 4-vinylpyridine (4VP). Substrates were pretreated in order to graft chloromethylbenzene (CMB) units capable of initiating the radical polymerization reaction of 4VP units. Surface characterization techniques, including Water Contact Angle (WCA), Attenuated Total Reflection (ATR), X-ray photoelectron spectroscopy (XPS), Atomic Force Microscopy (AFM) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) showed a successful grafting of a stable, smooth and homogenous layer of p4VP. This process offers the advantages of a rapid, simplified and low cost strategy to chemically modify polymer substrates with covalently bonded layer of the pH responsive p4VP for different applications. Moreover, by using TOF-SIMS profiling, we were able to track a density gradient along the z-axis generated by the interpenetrating phases of the different layers of the final modified surface. Fact that we correlated to the various positions of initiation sites within the polyethylenimine (PEI) used for PET aminolysis prior to CMB grafting. Our strategy will be used in future work to graft other polymers for different applications where industrial scale viable options are needed.

Synthesis and characterization of glycosylated nano particles

Abstract Functionalized polymer nanoparticles have been synthesized by emulsifier-free emulsion polymerization of styrene with amino-functionalized monomers. Two monomers were used: the well-known 2- aminoethylmethacrylate and a new monomer with a styrenic polymerizable function, 4-(2-aminoethylthio)methylstyrene. The latexes were characterized by gravimetry, dynamic light scattering and colorimetric titration in order to obtain the styrene conversion, the hydrodynamic diameter, the particle size distribution and the concentration of surface amino groups, respectively. Then, glycosydic molecules such as maltose, lactose, maltotriose and galactopyranosylethanal were covalently grafted to the nanoparticles by amidation or reductive amination.

Hydrophobization of chitosan films by surface grafting with fluorinated polymer brushes

Chitosan with its surface-properties and biodegradability is a promising biomaterial for green packaging applications. Till now, this application is still limited due to chitosan high sensitivity to water. Some existing studies deal with the incorporation of hydrophobic additives to enhance water-proof performances of chitosan films. As these additives may impair the film properties, our study focuses on chitosan efficient hydrophobization by means of simple and successful surface grafting reactions. Chitosan films prepared by solvent casting were modified by means of surface-initiated activators regenerated by electron transfer atom radical polymerization (SI-ARGET-ATRP) of 2-hydroxyethyl methacrylate (HEMA) followed by esterification reaction with fluorinated acyl compound. X-ray photoelectron spectroscopy (XPS), attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and Time-of-Flight Secondary Ion Mass Spectroscopy (ToF-SIMS) highlighted the surface chemical changes after each step. Surface properties were investigated by contact angle measurements and surface energy calculations. Hydrophobic surfaces with low surface energy and good water-repellent properties were obtained using a simple handling polymerization procedure. This is the first study in applying ARGET ATRP to prepare hydrophobic biopolymer films offering potential applications in packaging.