New Route to Polymeric Nanoparticles by Click Chemistry Using Bifunctional Cross-Linkers

A new route to functional polymeric nanoparticles (PNPs) of different chemical nature in the 3 to 20 nm size range is reported by combining both radical addition fragmentation chain transfer (RAFT) polymerization and “click” chemistry (CC) techniques. RAFT polymerization was employed for the synthesis of well-defined statistical copolymers with pending –Cl groups along the macromolecular chain. After transformation of the –Cl groups to –N₃ groups by treatment with sodium azide, an appropriate bifunctional cross-linker is employed to obtain PNPs under CC conditions promoting intramolecular cycloaddition (cross-linking). Following this new route, polystyrene, poly(alkyl (meth)acrylate), polymethacrylic acid, poly(sodium styrenesulfonate) and poly(N-isopropyl) NPs have been synthesized and in-deep characterized.     

Levels of polycyclic aromatic hydrocarbons,polychlorinated byphenyls,methylmercury and butyltins in the natural UNESCO reserve of the biosphere of Urdaibai (Bay of Biscay,Spain)

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), methylmercury (MeHg⁺) and butyltins (mono-, di- and tri-butyltin, MBT, DBT and TBT) were monitored in oysters (Crassostrea sp.) and sediments collected in different sampling points of the UNESCO reserve of the biosphere of Urdaibai (Bay of Biscay) from March 2006 to June 2007. In the case of oyster samples, concentrations in the 290–1814 µg kg^?1 (PAHs), 70–475 µg kg^?1 (PCBs), 75–644 µg kg^?1 (MeHg⁺) and 200–1300 µg kg^?1 (as a sum of the three butyltins) ranges were obtained. In most samples TBT was the most abundant butyltin, followed by DBT and MBT. It should be highlighted that most samples exceeded the highest range (367 µg kg^?1) found in the last mussel watch programme carried out by the National Oceanic and Atmospheric Administration (NOAA) for butyltins in oyster samples. This could be due to the presence of a shipyard in the estuary. Sediment concentrations ranged as follows: total PAHs (856–3495 µg kg^?1) and total PCBs (58–220 µg kg^?1). Organometallic species were always below the limits of detection (LODs) (0.24 µg kg^?1 for MeHg⁺, 0.6 µg kg^?1 for MBT, 0.48 µg kg^?1 for DBT and 1.1 µg kg^?1 for TBT). In both sediment and oyster PAH sources were mostly combustion. In the case of PCBs, 4-6 chlorine-atom congeners were the most abundant ones. Slight differences in the profile of PAHs as well as PCBs can be detected when the matrices were compared with each other. Finally, in the case of PAHs, sediment and water column played the main role in the accumulation pathway into the organisms in all the sampling stations.     

Kinetics of Core‐Shell Nanoparticle Formation by Two‐Dimensional Nuclear Magnetic Resonance

We have studied the kinetics of polymeric nanoparticle formation for poly(styrene‐block‐4‐vinylpyridine) [P(S‐b‐4‐VPy)], chains in a non‐selective solvent using 1,4‐dibromobutane (DBB) as a cross‐linker by means of different nuclear magnetic resonance (NMR) spectroscopy techniques. The kinetic process was followed using ¹H, ¹³C, and 2‐D Heteronuclear Single Quantum Correlation (HSQC) NMR experiments. The kinetic data obtained from 2‐D HSQC and ¹H NMR experiments were in good agreement between them, proving the reliability of the 2‐D HSQC NMR technique for the in situ study of the kinetics of core‐shell nanoparticle formation. A value of 1.5 × 10⁻⁵ s⁻¹ was determined for the apparent kinetic constant of the P(S‐b‐4‐VPy)‐DBB core‐shell nanoparticle formation process.

     

Room temperature self-healing power of silicone elastomers having silver nanoparticles as crosslinkers

Thiol-functionalised silicone-oils were crosslinked with silver nanoparticles to give mechanically consistent elastomers with high self-healing power. The materials were broken into small pieces and put together in intimate contact for 24 hours at room temperature, observing a complete macroscopic healing and a quantitative recovery of compression-stress and strain.     

Phase diagram and entropic interaction parameter of athermal all‐polymer nanocomposites

An entropic model is introduced for the prediction of the χ interaction parameter and phase diagram of athermal all‐polymer nanocomposites (chemically identical polymer‐nanoparticle/linear‐polymer blends). According to this model, dilution of contact (hard sphere‐like) nanoparticle/nanoparticle interactions upon mixing plays a key role in explaining the miscibility behavior of athermal all‐polymer nanocomposites in the presence of unfavorable chain expansion (or contraction) effects. The new model is valid both for the cases of chain stretching and chain contraction and provides an appropriate capture of entropy changes accompanying the mixing of chemically identical nanoparticles and polymers. A good agreement was found between predicted χ interaction parameter (χ_cal = ?2.3 × 10^?3) and reported small angle neutron scattering (SANS) experimental data ( ～ ?2 × 10^?3) for 211 kDa cross‐linked poly(styrene) (PS)‐nanoparticles dissolved in 473 kDa deuterated linear‐PS. In addition, the miscibility boundary calculated from the model for PS‐nanoparticle/linear‐PS nanocomposites (?₁ = 0.02) compared very favorably to that experimentally found. For this system, the spinodal line in the polymer radius of gyration (R_g) versus nanoparticle radius (a) phase diagram was found to follow the simple scaling law: , being the polymer radius of gyration at which the second derivative of the free energy of mixing vanishes. Finally, the model has been employed for the prediction of the entropic χ interaction parameter, the miscibility behavior, and the melting point depression of athermal poly(ethylene) (PE)‐nanoparticle/linear‐PE nanocomposites using recent chain dimension data from Monte Carlo (MC) simulations, where chain stretching or chain contraction effects were observed depending on nanoparticle size. Copyright © 2007 John Wiley & Sons, Ltd.     

A Nanotechnology Pathway to Arresting Phase Separation in Soft Nanocomposites

Direct observation of the miscibility improving effect of ultra‐small polymeric nanoparticles (radius ≈4 nm) in model systems of soft nanocomposites is reported. We have found thermodynamically arrested phase separation in classical poly(styrene) (PS)/poly(vinyl methyl ether) blends when PS linear chains were totally replaced by ultra‐small, single chain PS nanoparticles, as determined by thermo‐optical microscopy measurements. Partial arrested phase splitting on heating was observed when only some of the PS chains were replaced by unimolecular PS nanoparticles, leading to a significant increase of the lower critical solution temperature (LCST) of the system (up to 40 °C at 15 vol.‐% nanoparticle content). Atomic force microscopy and rheological experiments supported these findings. Thermodynamic arrest of the phase separation process induced by replacement of linear polymer chains by unimolecular polymer nanoparticles could have significant implications for industrial applications requiring soft nanocomposite materials with excellent nanoparticle dispersion in a broad temperature range.