A Versatile Strategy to Synthesize Perfluoropolyether-Based Thermoplastic Fluoropolymers by Alkyne-Azide Step-Growth Polymerization.

Perfluoropolyether (PFPE)-based thermoplastic fluoropolymers are synthesized by A2 + B2 step-growth polymerization between PFPE-diyne and fluorinated diazides. This versatile method allows synthesizing PFPE-based materials with tunable physicochemical properties depending on the exact nature of the fluorinated segment of the diazide precursor. Semicrystalline or amorphous materials endowed with high thermostability (≈300 °C under air) and low glass transition temperature (≈-100 °C) are obtained, as confirmed by differential scanning calorimetry, thermogravimetry, and rheometry. Step-growth polymerizations can be copper-catalyzed but also thermally activated in some cases, thus avoiding the presence of copper residues in the final materials. This strategy opens up new opportunities to easily access PFPE-based materials on an industrial scale. Furthermore, a plethora of developments can be envisioned (e.g., by adding a third trifunctional component to the formulations for the synthesis of PFPE-based elastomers).

Multi-Scale Study of a Phase Change Material on a Tropical Island for Evaluating Its Impact on Human Comfort in the Building Sector.

Our study explores the utilization of a phase change material (PCM) to optimize energy efficiency and thermal comfort in buildings in tropical climates. Employing a comprehensive multi-scale approach, this research encompasses both microscopic and macroscopic analyses to rigorously evaluate the PCM's performance under various environmental conditions. It evaluates the effect of PCMs on ambient conditions in the face of temperature variations and high humidity, utilizing experimental methods at different scales (microscopic and macroscopic). Microscopic analyses reveal the composite structure of the PCM, consisting of microencapsulated paraffin within a cellulose fiber matrix. At a macroscopic scale, experiments using two real-scale test cells evaluated thermal performance and its influence on thermal comfort. Temperature and humidity data were meticulously collected over an extended period to assess the PCM's impact on indoor regulation. We employed type T thermocouples and flux meters to monitor thermal dynamics and energy flux across the building walls. This setup facilitated a detailed comparison of temperature variations and thermal comfort metrics between the PCM-equipped test cell and a control cell. The results indicate a seasonal duality of the PCM: beneficial in winter for thermal regulation but problematic in summer due to excessive heat retention. The conclusions highlight the importance of carefully selecting and adapting PCMs for tropical climates, thus providing valuable insights for designing sustainable buildings in regions facing similar climatic challenges.

Investigation of the Reaction between a Homemade PEEK Oligomer and an Epoxy Prepolymer: Optimisation of Critical Parameters Using Physico-Chemical Methods.

Several researchers have examined the interest in using a thermoplastic to increase thermoset polymers' shock resistance. However, fewer studies have examined the nature of the mechanisms involved between both kinds of polymers. This was the objective of our work, which was carried out using a gradual approach. First, we describe the synthesis of a poly(ether ether ketone) oligomer (oPEEK) with hydroxyl terminations from the reaction of hydroquinone and 4,4'-difluorobenzophenone in N-methyl-2-pyrrolidone. Then, the main physicochemical properties of this oligomer were determined using different thermal analyses (i.e., differential scanning calorimetry (DSC), thermogravimetric (ATG), and thermomechanical analyses) to isolate its response alone. The chemical characterisation of this compound using conventional analytical chemistry techniques was more complex due to its insolubility. To this end, it was sulfonated, according to a well-known process, to make it soluble and enable nuclear magnetic resonance (NMR) and size exclusion chromatography (SEC) experiments. Additional information about the structural and chemical characteristics of the oligomer and its average molecular weight could thus be obtained. The synthesis of an oligoPEEK with α,ω-hydroxyl end-groups and a molecular weight of around 5070 g/mol was thus confirmed by NMR. This value was in accordance with that determined by SEC analysis. Next, the reaction of oPEEK with an epoxy prepolymer was demonstrated using DSC and dynamic rheometry. To this end, uncured mixtures of epoxy prepolymer (DGEBA) with different proportions of oPEEK (3, 5, 10 and 25%) were prepared and characterised by both techniques. Ultimately, the epoxy-oPEEK mixture was cured with isophorone diamine. Finally, topological analyses were performed by atomic force microscopy (AFM) in tapping mode to investigate the interface quality between the epoxy matrix and the oPEEK particles indirectly. No defects, such as decohesion areas, microvoids, or cracks, were observed between both systems.

Synthesis and characterization of a small library of bisglucosides: Influence of the nature of the diol/diphenol used in O-glucosylation.

In this paper, the synthesis of different bisglucosides is investigated through the reaction of two acetylated glucose units with a diol (or diphenol) in order to develop a versatile molecular platform for the future development of bio-based polymers. A panel of five diols and one diphenol is initially used in order to examine the influence of their chemical skeleton on the reaction yield and both nature and proportion of formed species. Reaction products are identified using 1H and 13C NMR spectroscopies completed by MALDI-TOF MS technique. The nucleophilicity of these dihydroxy compounds is identified as being the main factor that governs the reaction characteristics. In particular, the best selectivity is obtained with the use of hydroquinone. Inversely, by-products (oligomers, deacetylated compounds) are observed with the diols defined by higher nucleophilicity despite the choice of stereoselective pathway using acyl protecting groups.

Optimized Synthesis According to One-Step Process of a Biobased Thermoplastic Polyacetal Derived from Isosorbide.

This paper describes both the synthesis and characterization of a biobased and non-aromatic polyacetal produced from the reaction between isosorbide and methylene chloride. The reaction was conducted in an aprotic dipolar and harmless solvent using a one-step, fast and economical procedure. The chemical composition of this polymer was investigated using Nuclear Magnetic Resonance and Fourier Transform Infra-Red spectroscopies. The molecular weights were examined by size exclusion chromatography and MALDI-TOF spectrometry. The synthesis conditions (concentration, mixing speed, solvent nature, stoichiometry, addition mode of one reactan) were found to strongly influence both polymer architecture and reaction yield. Under moderated stirring conditions, the polyacetal was characterized by a larger amount of macro-cycles. Inversely, under higher intensity mixing and with an excess of methylene chloride, it was mainly composed of linear chains. In this latter case, the polymeric material presented an amorphous morphology with a glass transition temperature (Tg) close to 55 °C. Its degradation temperature was evaluated to be close to 215 °C using thermogravimetry according to multi-ramp methodology. The chemical approach and the physicochemical properties are valuable in comparison with that characteristic of other isosorbide-based polyacetals.

High Temperature Epoxy Foam: Optimization of Process Parameters.

For many years, reduction of fuel consumption has been a major aim in terms of both costs and environmental concerns. One option is to reduce the weight of fuel consumers. For this purpose, the use of a lightweight material based on rigid foams is a relevant choice. This paper deals with a new high temperature epoxy expanded material as substitution of phenolic resin, classified as potentially mutagenic by European directive Reach. The optimization of thermoset foam depends on two major parameters, the reticulation process and the expansion of the foaming agent. Controlling these two phenomena can lead to a fully expanded and cured material. The rheological behavior of epoxy resin is studied and gel time is determined at various temperatures. The expansion of foaming agent is investigated by thermomechanical analysis. Results are correlated and compared with samples foamed in the same temperature conditions. The ideal foaming/gelation temperature is then determined. The second part of this research concerns the optimization of curing cycle of a high temperature trifunctional epoxy resin. A two-step curing cycle was defined by considering the influence of different curing schedules on the glass transition temperature of the material. The final foamed material has a glass transition temperature of 270 °C.

Determination of the structure of the organized phase of the block copolymer PEO-PPO-PEO in aqueous solutions under flow by small-angle neutron scattering.

The organization of Tetronic 908 (T908), a star copolymer of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) blocks, has been examined. Above critical conditions of temperature and concentration, the micelles formed by the aggregation of PPO units self-organize into particular structures. While small-angle neutron scattering (SANS) characterizations performed with static conditions demonstrate the organization of the medium, the experimental results do not allow us to make a distinction between simple cubic and body-centered-cubic structures. However, SANS measurements realized under shear produce characteristic diffraction diagrams. In this paper, an accurate methodology is proposed to identify, without ambiguity, the exact nature of the organized phase. Applied to our system, indexing of the diffraction pattern spots reveals that the organization of T908 is of bcc type oriented with the [111] direction parallel to the direction of flow, but the crystals can present any orientation about this direction. The lattice size has been estimated and compared to previous published results.

Nanostructure in block copolymer solutions: rheology and small-angle neutron scattering.

Triblock copolymers composed of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) present an amphiphilic character in aqueous solutions. Since PPO is less hydrophilic than PEO and since their solubilities decrease when the temperature increases, the copolymers self-assemble spontaneously, forming micelles at moderate temperatures. For higher temperatures or concentrations, the copolymers or the micelles are ordered because of repulsive interactions and form lyotropic liquid crystalline phases. These are phases of very great viscosity with the aspect of gels, and transitions between different crystalline phases can occur at fixed concentration during an increase of temperature. We studied solutions of three different copolymers. The first two have a star structure. They are both composed of four branches (EO)x (PO)y fixed on an ethylene diamine, but differ by the values of x and y . Their commercial name is Tetronic 908 (x=114, y=21) and Tetronic 704 (x=16, y=18) . The third copolymer (EO)37(PO)56(EO)37 is linear and is known under the name of Pluronic P105 . The measurements of the shear complex elastic modulus according to the temperature is used to determine the temperatures of the different transitions. Then, small-angle neutron scattering on samples under flow and true crystallographic arguments make it possible to identify the nature of the crystalline phases. For the systems studied, we show that the branched copolymers form only one type of liquid crystalline phase, which is bcc for the T908 and lamellar for the T704 . For the linear copolymer, it is possible to identify three transitions: micellar solution to hexagonal phase, hexagonal phase to body-centered cubic phase, and finally body-centered cubic phase to lamellar phase.

Influence of both cation and alginate nature on the rheological behavior of transition metal alginate gels.

The rheological properties of several ionotropic alginate hydrogels were investigated according to the nature of the divalent cation (Mn(2+), Co(2+), Cu(2+)) and the guluronic fraction of the alginate (HG and LG for "high G-content" and "low G-content"). Six hydrogels (Mn-LG, Mn-HG, Co-LG, Co-HG, Cu-LG and Cu-HG) were synthesized and studied by spectromechanical analyses. On one hand, Cu-HG, Cu-LG and Co-HG behaved as viscoelastic solids: the elastic contribution was higher than the dissipative component in all the frequency range studied (G'>G"). No flow zone (G">G') was detected even at very low values of the shearing frequency. On the other, Mn-HG, Mn-LG and Co-LG presented a spectromechanical behavior that resembled that observed classically for entangled polymers. Indeed, at high frequency, these latter materials could be compared to a viscoelastic solid but at low frequency, the flow zone was described and the viscous character became prevalent with finite relaxation time. Very good correlations with the microscopic structurations of the network were evidenced (rubbery vs. flow zone and fibrillar vs. complex morphology respectively).