Dispersion of Carbon Nanotubes Through Amphiphilic Block Copolymers: Rheological and Dielectrical Characterizations of Poly(ethylene oxide) Composites

In this article, we report on some properties of polymer nanocomposites prepared from dispersions of multi-wall carbon nanotubes (CNT) in aqueous solution prepared using amphiphilic block copolymers. These nanocomposites are made of polyethylene oxide as matrix and CNT wrapped with copolymers as fillers. We investigated the rheological and electrical behavior of such composites with the objectives of underlined the effect of wrapping. Two rheological and only one electrical percolation thresholds have been observed and related to polymer-CNT and CNT-CNT networks. The low values of these percolation thresholds agree with a homogeneous dispersion of CNT in the matrix. We also demonstrated that specific wrapping may induce an increase of electrical conductivity without affecting too much the viscosity of the melt

Synthesis of polyester-polypeptide diblock and triblock copolymers using amino poly(epsilon-caprolactone) macroinitiators

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Poly(methyl methacrylate)-poly(caprolactone) AB and ABA block copolymers by combined ring-opening polymerization and atom transfer radical polymerization

Chemical modification of alpha-hydroxy,omega-isopropylestertelechelic iPrO-PCL-OH, 1, and alpha,omega-dihydroxytelechelic HO-PCL-OH, 4, poly(epsilon-caprolactone) (PCL), synthesized from ring-opening polymerization using La((OPr)-Pr-i)(3) or Sm(BH4)(3)(THF)(3), allows the synthesis of the corresponding alpha-bromoester end-funetionalized polymers iPrO-PCL-.Br, 2, and Br-PCL-Br, 5, respectively. This direct procedure consists in an esterification of the hydroxy group(s) of 1 and 4 using 2-bromoisobutyryl bromide. These bromopolyesters 2 and 5 have subsequently been used as macroinitiators to synthesize, via atom transfer radical polymerization of methyl methacrylate (MMA), the new set of di- and triblock polyester-polyacrylate copolymers PCL-b-PMMA, 3, and PMMA-b-PCL-b-PMMA, 6, respectively. All (co)polymers are well defined as characterized by NMR and size exclusion chromatography analyses. In addition, the thermal properties of copolymers 3 and 6 have been investigated by differential scanning calorimetry. The self-assembly of triblock PMMA-b-PCL-b-PMMA, 6, copolymers into nanoparticles has been investigated by dynamic light scattering, atomic force microscopy, and optical microscopy techniques

Equilibrium anionic ring-opening polymerization of a six-membered cyclosiloxazane

The anionic ring-opening polymerization of heptamethyl-1,3-dioxa-5-aza-2,4,6-trisilacyclohexane, initiated with organolithium compounds, has been investigated. With the addition of dimethylformamide (DMF), the polymerization is controlled. Backbiting reactions are limited and give a unique specific cyclic compound in low proportion. Thermodynamic and kinetic studies indicate that such polymerization is equilibrated. The apparent rate constants of propagation and depolymerization along with the thermodynamic parameters (enthalpy and entropy) of the polymerization have been calculated. The active species are ion pairs externally solvated by DMF in equilibrium with unreactive aggregated ion pairs

Synthesis and Self-Assembly Properties of Peptide-Polylactide Block Copolymers

Poly(L-lactide-b-gamma-benzyl glutamate) copolymers with various block lengths were synthesized by sequential ring-opening polymerization of L-lactide and N-carboxyanhydride of gamma-benzyl glutamate. The copolymers were characterized by SEC and NMR spectrometry. DSC and SAXS data suggested that the copolymers were phase-separated in domains containing either crystalline PLLA or liquid-crystalline columnar hexagonal morphology of PBLG. When varying the temperature, reversible local order-order transition could be observed on these diblock copolymers

Glycolipids as a source of polyols for the design of original linear and cross-linked polyurethanes

Two novel sugar-based fatty ester polyols were synthesized by selective transesterification of epoxidized methyl or ethyl oleate with unprotected methyl alpha-D-glucopyranoside and sucrose respectively, followed by hydrolysis of the epoxide moiety. The so-formed polyols were then used as polyurethane (PU) precursors in the polyaddition with isophorone diisocyanate (IPDI) in the presence of dibutyl tin dilaurate (DBTDL) as a catalyst. Interestingly, the reactivity of the hydroxyl functions attached to the sugar and to the fatty ester chain moieties respectively could be discriminated with respect to the solvent used, enabling the synthesis of either linear or cross-linked PUs. The linear PUs were studied by means of FTIR, H-1 NMR spectroscopy and size exclusion chromatography, SEC. The thermo-mechanical properties of these original PUs bearing pendant or intramolecular sugar units were also analyzed by differential scanning calorimetry, DSC

The preparation of carbon nanotube/poly(ethylene oxide) composites using amphiphilic block copolymers

Polymer/multiwall carbon nanotube (MWCNT) composites were prepared by using amphiphilic block copolymers as dispersant. First, MWCNTs were wrapped with amphiphilic block copolymers in aqueous solution. Poly(ethylene oxide) was selected as the hydrophilic block because of its strong affinity with water while one of the following polymers: poly(ethylene), poly(butadiene), poly(styrene), poly(propylene oxide), or poly(thiophene) was used as the hydrophobic block of the copolymers. The dispersions were characterized by optical microscopy and transmission electron microscopy along with UV-Visible adsorption and dynamic light scattering. Based on the results, we could assess the effect on CNT dispersion quality of both, the molar mass of copolymers, the nature of the hydrophobic block and the length of hydrophilic block. The crystallization behavior of composites prepared from these dispersions was investigated. Results were related to the dispersion of the nanoparticles in the polymer matrix