François Ganachaud

On the versatility of urethane/urea bonds: reversibility, blocked isocyanate, and non-isocyanate polyurethane.

Isocyanate, and Non-isocyanate Polyurethane Etienne Delebecq,† Jean-Pierre Pascault,‡,§ Bernard Boutevin,† and Franco̧is Ganachaud*,†,‡,§ †Institut Charles Gerhardt, UMR 5253 CNRS, Ingeńierie et Architectures Macromolećulaires, Ecole Nationale Supeŕieure de Chimie de Montpellier, 8 rue de l’ećole normale, 34296 Montpellier, Cedex 05, France ‡INSA-Lyon, IMP, UMR5223, F-69621, Villeurbanne, France Universite ́ de Lyon, F-69622, Lyon, France

New Synthetic Strategies for Structured Silicones Using B(C6F5)3

The dehydrocarbonative condensation of alkoxysilanes + hydrosilanes in the presence of the Lewis acid catalyst B(C6F5)3 (R3SiOR′ + HSiR3 ′′ → R3SiOSiR3 ′′ + R ′ H) – described throughout this review as the Piers-Rubinsztajn reaction – provides a new, mild strategy for the controlled synthesis of silicones. In this review we examine the mechanistic parameters that control the reaction, and outline the types of accessible small molecules, linear, branched, and cross-linked materials (resins and elastomers) that can be prepared using this and related reactions.

Silicon Based Polymers

Silicon Based Polymers presents highlights in advanced research and technological innovations using macromolecular organosilicon compounds and systems, as presented in the 2007 ISPO congress. Silicon-containing materials and polymers are used all over the world and in a variety of industries, domestic products and high technology applications. Among them, silicones are certainly the most well–known, however there are still new properties discovered and preparative processes developed all the time, therefore adding to their potential. Less known, but in preparation for the future, are other silicon containing-polymers which are now close to maturity and in fact some are already available like polysilsesquioxanes and polysilanes. All these silicon based materials can adopt very different structures like chains, dendrimers, hyperbranched and networks, physical and chemical gels.

Simple but precise engineering of functional nanocapsules through nanoprecipitation.

A general, rapid, and undemanding method to generate at will functional oil-filled nanocapsules through nanoprecipitation is reported. On the basis of polymer and hexadecane/water/acetone phase diagrams, the composition can be set so that polymer chains preferentially stick at the interface of the oil droplets to create nanocapsules. The nanocapsules can be decorated with biorelevant molecules (biotin, fluorescent tags, metal nanoparticles) within the shell and loaded with hydrophobic molecules in a simple one-pot procedure.

Looking over Liquid Silicone Rubbers: (2) Mechanical Properties vs Network Topology

In the previous paper of this series, eight formulations were analyzed under their uncross-linked forms to relate liquid silicone rubber (LSR) chemical compositions to material network topologies. Such topologies were confirmed by swelling measurements and hardness evaluation on vulcanized samples. In this article, characterization of cross-linked materials is further done using different mechanical measurements on final materials, including dynamic mechanical analysis, compression set, stress-strain behavior and tear resistance. It was shown that the compression set value is mainly related to the chains motion: increasing the filler-polymer interactions and/or decreasing the dangling/untethered chains content positively impact the compression resistance. Elongation at break depends on the molar mass between cross-linking points, showing an optimum value set at around 20 000 g mol(-1), i.e., the critical mass between entanglements. The distribution of elastic strands into the network has strong implications on the stress-strain curves profiles. By generating bimodal networks, the ultimate properties are enhanced. The materials cured by hydride addition on vinyl groups catalyzed by peroxide exhibit poorer compression set and tensile strength values, respectively, because of post-cross-linking reaction and broad polydispersity index of elastic network chains.

Looking over liquid silicone rubbers: (1) network topology vs chemical formulations.

This study proposes a comprehensive study on liquid silicone rubber (LSR) formulations to unravel which components (among functional polydimethylsiloxane polymers and modified silica fillers) improve the mechanical properties of the final materials. In this first part, various industrial products have been deformulated using conventional chemical analyses. The silica content and their surface chemistry were assessed by TGA. Architecture and molar mass of polymers were deduced from (29)Si NMR and SEC in toluene, respectively. Relative concentrations of hydride and vinyl reactive groups and stoichiometric imbalance (r = nSiH/nSiVi) were quantified by proton NMR. Stoichiometric imbalance is slightly higher than 1.5 for cross-linker with hydride functions well redistributed along the chain, whereas for some formulations, rs as high as 3.7 were implemented. These variations has strong implications on the cross-linking density of the final material, since the remaining hydride groups react together and decrease the molar mass between cross-links. From the comparison between formulations, it was shown that hardness adjustment is mainly performed by playing on two parameters: filler content and molar mass between cross-linking points for hardness ranging from 20 to 30 Shore A. Above this limit, it is necessary to modify the silica surface with reactive groups, such as vinyl functions. Surprisingly, two formulations were shown to use a dual cross-linking catalysis systems, peroxide and platinum, leading to efficient and full cure even at lower temperature (typically 140 °C). Network topologies were estimated from the predicted chemistry of the materials in a final discussion part.

Finest nanocomposite films from carbon nanotube-loaded poly(methyl methacrylate) nanoparticles obtained by the Ouzo effect

Composite particles, i.e. PMMA nanoparticles trapping one to a few nanotubes in their core, were prepared by a derivative process of the solvent shifting technique, also called the “Ouzo effect”. Particles were converted by simple annealing into nanocomposite films, the thermal resistance of which was evidenced by microcalorimetry and thermogravimetry.

How I met your elastomers: from network topology to mechanical behaviours of conventional silicone materials

Silicone elastomers are available in different formulations that are mainly discriminated by their crosslinking mechanisms. Different chemical networks lead to diverse mechanical behaviours. This work aims at comparing three types of conventional silicone elastomers, one Liquid Silicone Rubber (LSR), one High Consistency Rubber (HCR) and one, thermoplastic, hydrogen bonded cross-linked elastomer (TPE). Each one is studied and compared in terms of network microstructure versus mechanical behaviour.

Pulsed‐laser polymerization (PLP) of N‐isopropyl acrylamide (NIPAM) in water: a qualitative study

Pulsed-laser polymerization results are presented for N-isopropyl acrylamide (NIPAM) in water; the data show the overtones that satisfy one of the PLP consistency tests. Apparent propagation rate coefficients k(p,app) were measured; these decrease with increasing concentrations of initiator, monomer and polymer, sugeestina significant association between the various species involved. The PLP data also qualitatively show the presence of low rates of termination and transfer.

Cationic polymerization of isobutyl vinyl ether in aqueous media: physical chemistry tricks to fight against thermal runaway

Cationic polymerization of isobutyl vinyl ether (IBVE) in aqueous media (suspension, dispersion or emulsion), using mainly BF3OEt2 as a co-initiator is reported. A high exotherm was observed while carrying out the polymerization in aqueous suspension, whereas in dispersion (mixture of water and n-hexane as reaction medium) or in emulsion particularly, efficient heat transfer decreased thermal runaway. Poly(isobutyl vinyl ether)s with Mn up to 8600 g mol−1 and relatively broad molecular weight distribution (Mw/Mn = 2.5–3.5) in high yield (>85%) were synthesized in aqueous dispersion. In direct emulsion, using BRIJ®98 (7 wt% to monomer) as a surfactant, polymers of low molecular weight (Mn ≤ 2000 g mol−1) and relatively narrow molecular weight distribution (Mw/Mn = 2.0–2.5) were obtained in moderate yields (50–60%), whereas, in inverse emulsion (water–n-hexane as a reaction medium), higher yields (85–96%) and higher molecular weights (Mn = 4500–5500 g mol−1) were reached. Chain-end analyses by means of 1H NMR spectroscopy revealed that most of the chains contain acetal end groups (typically ≥80%), while aldehyde (12–16%) and alkenal (0.5–3.5%) end groups were found in minor proportions.