Cédric Calberg

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).

Electrical and dielectric properties of carbon black filled co-continuous two-phase polymer blends

The electrical and dielectric properties of co-continuous polystyrene (PS)/poly(methylmethacrylate)(PMMA) blends loaded with carbon black (CB) of a special grade (BP 1000) have been studied. They strongly depend on the selective localization of the CB particles at the blend interface quite consistently with the double percolation concept. The interfacial localization of CB contributes to the stabilization of the phase morphology against thermal post treatment. Nevertheless, the sample annealing has a very favourable effect on the percolation threshold that decreases. The composition range in which phases are co-continuous is also increased by the addition of the filler. Dispersion of the conductance and the dielectric constant has been measured in the wide frequency range 10-4-108 Hz for blends containing 0-5 wt% CB. On the basis of these results, the mechanism of electrical transport (trapping, hopping, tunnelling, percolation) has been discussed in relation to the CB loading and the optimum loading has been identified for the electrical and dielectric properties to be stable and reproducible.

Poly(e-caprolactone) layered silicate nanocomposites: effect of clay surface modifiers on the melt intercalation process

Abstract Nanocomposites based on biodegradable poly(e-caprolactone) (PCL) and layered silicates (montmorillonite) modified by various alkylammonium cations were prepared by melt intercalation. Depending on whether the ammonium cations contain non-functional alkyl chains or chains terminated by carboxylic acid or hydroxyl functions, microcomposites or nanocomposites were recovered as shown by X-ray diffraction and transmission electron microscopy. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. The layered silicate PCL nanocomposites exhibited some improvement of the mechanical properties (higher Young’s modulus) and increased thermal stability as well as enhanced flame retardant characteristics as result of a charring effect. This communication aims at reporting that the formation of PCL-based nanocomposites strictly depends on the nature of the ammonium cation and its functionality, but also on the selected synthetic route, i.e. melt intercalation vs. in situ intercalative polymerization. Typically, protonated w-aminododecanoic acid exchanged montmorillonite allowed to intercalate ε -caprolactone monomer and yielded nanocomposites upon in situ polymerization, whereas they exclusively formed microcomposites when blended with preformed PCL chains. In other words, it is shown that the formation of polymer layered silicate nanocomposites is not straightforward and cannot be predicted since it strongly depends on parameters such as ammonium cation type and functionality together with the production procedure, i.e., melt intercalation, solvent evaporation or in situ polymerization.

Copper bromide complexed by fluorinated macroligands: towards microspheres by ATRP of vinyl monomers in scCO2

We report the successful synthesis of poly(methyl methacrylate) (PMMA) by atom transfer radical polymerization using a catalyst ligated to a polymeric ligand having a dual role, i.e., the complexation of the copper salt and the stabilization of the growing PMMA particles; at the end of the polymerization, the catalyst is removed by supercritical fluid extraction leading to PMMA microspheres with low residual catalyst content.

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).

Synthesis of Biodegradable Poly-ε-caprolactone Microspheres by Dispersion Ring-Opening Polymerization in Supercritical Carbon Dioxide

A series of fluorinated diblock and triblock copolymers of poly(epsilon-caprolactone) and poly(heptadecafluorodecylacrylate) were prepared by combining ring-opening polymerization of epsilon-CL and atom transfer radical polymerization of the acrylate. These copolymers with well-controlled molecular weight and composition were characterized by (1)H NMR spectroscopy and used as stabilizers for the dispersion ring-opening polymerization of epsilon-CL in supercritical carbon dioxide. The effect of composition and architecture of the polymeric stabilizers on the stabilization of PCL microspheres was investigated. Finally, purification of PCL was successfully implemented by reactive supercritical fluid extraction of the tin catalyst.

Supported ATRP of fluorinated methacrylates in supercritical carbon dioxide: preparation of scCO2 soluble polymers with low catalytic residues

Synthesis of poly(2,2,2-trifluoroethyl methacrylate) by supported ATRP was investigated in supercritical carbon dioxide using a copper salt ligated to a polymeric ligand immobilised onto silica; after polymerisation, fluorinated polymers with well defined molecular weight and low polydispersity were obtained.

Solvent effect on the electrografting of acrylonitrile on nickel

Abstract The effect of solvent on the reductive electrografting of acrylonitrile (AN) onto nickel cathodes has been studied in dimethylformamide (DMF), a solvent for polyacrylonitrile (PAN), and in non-solvents that include acetonitrile (ACN), propylene carbonate (PC) and pyridine (PY). Electrografting responsible for the cathode inhibition has been observed for the first time in PC and PY. Not only the polymer—solvent interactions but also the intrinsic polarity of the solvent have an effect on the intensity of the inhibition peak which is the signature of the electrografting reaction. Concentration of the monomer in the electrode double layer appears to decrease as the solvent polarity is increased, consistently with a more efficient displacement of the monomer by a more polar compound. That such a competition occurs is also supported by the effect of the nature and concentration of the conducting salt. The best quality films are formed in DMF, which is a solvent for PAN. Quartz microbalance experiments have emphasized the crucial importance of the potential range used for the AN electroreduction, particularly in a solvent of the polymer.

Characterization of polyacrylonitrile films grafted onto nickel by ellipsometry, atomic force microscopy and X-ray reflectivity

The thickness and roughness of polyacrylonitrile films electrografted on a nickel surface have been measured by ellipsometry atomic force microscopy and X-ray reflectivity. From combined ellipsometry and X-ray reflectivity measurements, accurate values for the refractive indices of polyacrylonitrile and nickel have been derived at a 6328-Angstrom wavelength. Dependence of the film thickness on the monomer concentration has been quantified for the first time. Furthermore, the thickness of the polyacrylonitrile (PAN) film is related to the nature of the solvent, depending on whether it is a good solvent for PAN (dimethylformamide; DMF) or not (acetonitrile; ACN)

Electrochemistry of N-vinyl-2-pyrrolidone and a non polymerizable analogue

Abstract According to previous studies, the electropolymerization of N-vinyl-2-pyrrolidone fits a cationic mechanism with grafting of the polymer onto the platinum anode. However, this article shows that the pyrrolidone substituent of N-VP is also involved in the anodic reaction in addition to the polymerizable vinyl double bond. This additional reaction in the potential range of interest was confirmed by the electrochemical oxidation of a non polymerizable analogue of N-VP, i.e. N-methylpyrrolidone. Therefore, at least two mechanisms can contribute to the electrodeposition of a polymer film in a solvent of poly N-VP: electrografting and polymer branching and/or crosslinking by species stemming from the electrooxidation of the pyrrolidone rings.