Copolymers of ethylene and butadiene were prepared using the ansa-bisfluorenyl Me2Si(C13H8)2NdR complex in combination with dialkylmagnesium as a chain transfer agent. Thorough kinetic studies and computational mechanistic investigations of this copolymerization reaction were performed. Combined with detailed analyses of the polymer microstructure and chainends, these studies demonstrate that the entitled copolymerization operates according to a living coordinative chain transfer copolymerization of ethylene and butadiene. Besides, in addition to the formation of the previously described 1,2-cyclohexane inner chain cyclic motif, the presence of bicyclic 1,5-decalin units via the formation of transient vinylcyclohexyl-methyl chain-end is discussed in the present communication. The non-accumulation of the vinylcyclohexane motif within the chains is explained by the reversibility of its formation, as interpreted with the help of DFT calculations, or by its rapid conversion into decalin motif after one ethylene insertion. Finally, this study also illustrates the ability of the fluorenyl ligand to adjust its binding mode on demand in order to avoid inhibition of catalyst.

Authors would like to thank Christine LUCAS for help in solid state NMR experiments, C2P2 (Chemistry, Catalysis, Polymer & Processes), UMR 5265 - University of Lyon 1.International audienceA new silicophosphorylated filler was generated in situ in a molten PA66 copolymer during extrusion process with the aim to improve the fire behavior of the matrix. The filler was obtained in one step via hydrolysis-condensation reactions of SiDOPO precursor (DOPO, 9,10-dihydro-9-oxa-10-phosphaphenanthrene). The synthesis of the precursor is reported and characterized by NMR. A Si-29 NMR study of SiDOPO hydrolysis-condensation reactions in N-methylacetamide (NMA) solvent was also conducted. Thermal stability of Cop-PA/SiDOPO composite and the major degradation products were studied by thermogravimetric analysis coupled with Infrared spectrometry (TGA/FTIR). The Pyrolysis Combustion Flow Calorimeter (PCFC) and cone calorimeter were used to investigate the fire behavior of the composite. Results show that the nanocomposite exhibits a little earlier ignition but with a decrease around 33% of the peak of heat release rate (PHRR). The presence at low concentration of silicon (0.65 wt.%) and phosphorus (0.75 wt.%) promotes the formation of an expanded char layer that acts as a barrier. A reduction of about 18% in effective heat of combustion (EHC) values suggests an additional flame inhibition effect of phosphorus in the gas phase

No abstract

Gold nanoclusters (AuNCs) are an emerging class of nanomaterials for bioimaging, featuring high photostability, sizedependent luminescence, large Stokes shifts, long photoluminescence lifetimes, and good biocompatibility. However, when stabilized by small ligands, AuNCs exhibit a limited colloidal stability. Here, we report the synthesis of original "hairy" AuNCs with a diameter under 2 nm and NIR photoluminescence (for both one-photon and two-photon excitation), stabilized by biocompatible end-grafted poly(N-acryloyl morpholine) (PNAM) chains prepared by RAFT polymerization. The AuNCs synthesis was carried out directly in water in the presence of thiol-terminated PNAM-SH chains. Compared with AuNCs stabilized by small ligands, our PNAM-AuNCs exhibit much better colloidal stability (unchanged for more than two months), a 2-fold increase in photoluminescence lifetimes, and significantly enhanced quantum yields. Moreover, their properties could be successfully tuned using PNAM chains with molecular weights ranging from 3000 to 11 000 g•mol −1 . These PNAM-AuNCs offer an excellent platform for the development of bioimaging probes without organic dyes.

No abstract

No abstract

Polyimides are commonly synthesized in a 2-step solution polymerization process. Such process requires long reaction times as well as specific care due to the use of potentially harmful solvents. In the present study, the total reaction time for producing polyimides has been lowered to less than 10 min by using a solvent-free continuous reactive extrusion process. The proof of concept was determined with the system based on 3,3',4,4'benzophenone-tetracarboxylic dianhydride (BTDA) and an aliphatic diamine, Jeffamine D-230 within a micro-extruder. Conversion degrees to polyimide, determined with 13 C NMR and DSC analysis, are over 90 mol% after 5 min of extrusion at 180 °C, 200 °C and 225 °C respectively. These syntheses were then transferred to a twin-screw extruder to form linear aliphatic-aromatic polyimides with two types of dianhydride: BTDA and pyromellitic dianhydride (PMDA). Comparison with a conventional solution polymerization process showed no significant differences in the polymers characteristics. The polyimides produced with this method presented glass transition temperatures ranging from 5 to 90 °C. The number average molar masses measured were between 11000 and 15000 g.mol -1 .

No abstract