Gérald Lopez

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).

Synthesis and microstructural characterization of poly(chlorotrifluoroethylene-co-vinylidene chloride) copolymers

The radical copolymerization of chlorotrifluoroethylene (CTFE) with vinylidene chloride (VDC) was investigated. A surfactant-free emulsion polymerization process was used to obtain poly(CTFE-co-VDC) copolymers of high molecular weight in up to 75 wt% yield. In parallel, a solution polymerization process afforded a range of poly(CTFE-co-VDC) copolymers of lower molecular weight and soluble enough to allow a meticulous characterization by NMR spectroscopy. Various statistical poly(CTFE-co-VDC) copolymers were synthesized, containing from 3 to 38 mol% of VDC. A triple resonance (1H/13C/19F) 2D-NMR 1H{13C}-HSQC (heteronuclear single quantum coherence) experiment was used to aid with resonance assignments and provided crucial information about monomer sequences. Quantitative 19F and 1H 1D-NMR enabled the determination of the composition of the copolymers. In all cases, CTFE is the less reactive of both comonomers. Decomposition temperature at 10% weight loss (T10%d values), ranged from 333 up to 400 °C under air, and a decreasing trend of the thermal stability was observed when increasing the VDC amount in the copolymer. These variations of the thermal properties were attributed to an increase in the number of C–H bonds broken in polymers with higher VDC molar percentages in the copolymer. Moreover, glass transition (Tg) and melting (Tm) temperatures ranged from 12 to 47 °C, and 162 to 220 °C, respectively.

Radical telomerization of fluorinated alkenes with dialkyl hydrogenophosphonates

This review summarizes various surveys on the synthesis of fluoroalkyl phosphonate derivatives by radical telomerization of fluorinated olefins with dialkyl H-phosphonates. For the past fifty years, numerous authors have reported such reactions involving a wide range of fluorinated olefins. Each class of fluorinated olefins is discussed in a dedicated paragraph, along with the influence that different parameters may have on the telomerization reactions: the nature of the solvent, the initial molar ratio of the reactants, the effect of the alkyl chain length of the H-phosphonates, and the nature of the initiator. Special attention has been given to the reported NMR data related to the adducts resulting from such reactions. The work discussed here opens up opportunities for further investigations that could deepen the knowledge on fluorinated derivatives of phosphonic acid.

Investigation of a novel fluorinated surfactant-based system for the design of spherical wormhole-like mesoporous silica

In contrast to hydrogenated based systems that led to many studies, fluorinated surfactants have been little reported. Thanks to their high chemical and thermal stability, these compounds are considered as suitable candidates for the synthesis of porous materials with an enhanced hydrothermal stability. This study reports the synthesis of a new fluorinated surfactant, 2-trifluoromethyl-7,7,8,8,9,9,10,10,11,11,12,12,12-tridecafluoro-4-thia-1-dodecanoic acid (FSC) obtained from the thiol-ene radical addition of 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluoro-1-octanethiol onto 2-trifluoromethyl acrylic acid in 85% yield. In the aim of achieving micelles in water to design mesoporous materials according to the cooperative templating mechanism, FSC was modified with water-soluble telechelic diamine (Jeffamine) ED-600. The modified surfactant was deeply characterized by spectroscopic methods and the FSC-Jeffamine ED-600 micellar system was used as porogen to prepare mesoporous materials via the cooperative templating mechanism. Spherical wormhole-like mesostructured silica materials of high specific surface area (850m2/g) and homogeneous pore size distribution (ca. 3.4nm) were obtained by conveniently adjusting the porogen/silica molar ratio and the hydrothermal conditions.

Radical copolymerisation of chlorotrifluoroethylene with isobutyl vinyl ether initiated by the persistent perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical

Results of the radical copolymerisation of chlorotrifluoroethylene (CTFE) with isobutyl vinyl ether (iBuVE) initiated by ˙CF3 radicals generated by β-scission of perfluoro-3-ethyl-2,4-dimethyl-3-pentyl radical (PPFR) at 90 °C in a batch reactor are reported. 19F NMR spectroscopy enabled the assessment of the molecular weights of the poly(CTFE-alt-iBuVE) copolymer by end-group analysis. It was found that, at low initiator concentrations (≤10 mol%), the ˙CF3 radicals preferably attack the vinyl ether monomer to initiate chain propagation and produce alternating poly(CTFE-alt-iBuVE) copolymers. At initiator ratios of 20 mol%, 19F NMR signals in the CF3 region other than the expected CH2–CF3 are observed and are attributed to ˙CF3 addition patterns due to kinetic effects brought on by monomer solubility. The molecular weights for the copolymer produced from 1%, 5%, and 10% PPFR were found to be 340 000, 237 000 and 122 000 g mol−1, respectively. The copolymer produced from 20% PPFR was oligomeric in nature with a molecular weight of 18 000 g mol−1.

19F DOSY diffusion-NMR spectroscopy of fluoropolymers

A new pulse sequence for obtaining 19F detected DOSY (diffusion ordered spectroscopy) spectra of fluorinated molecules is presented and used to study fluoropolymers based on vinylidene fluoride and chlorotrifluoroethylene. The performance of 19F DOSY NMR experiments (and in general any type of NMR experiment) on fluoropolymers creates some unique complications that very often prevent detection of important signals. Factors that create these complications include: (1) the presence of many scalar couplings among 1H, 19F and 13C; (2) the large magnitudes of many 19F homonuclear couplings (especially 2JFF); (3) the large 19F chemical shift range; and (4) the low solubility of these materials (which requires that experiments be performed at high temperatures). A systematic study of the various methods for collecting DOSY NMR data, and the adaptation of these methods to obtain 19F detected DOSY data, has been performed using a mixture of low molecular weight, fluorinated model compounds. The best pulse sequences and optimal experimental conditions have been determined for obtaining 19F DOSY spectra. The optimum pulse sequences for acquiring 19F DOSY NMR data have been determined for various circumstances taking into account the spectral dispersion, number and magnitude of couplings present, and experimental temperature. Pulse sequences and experimental parameters for optimizing these experiments for the study of fluoropolymers have been studied. Copyright

Synthesis of Fluorinated Telechelic Diols Based on 3,3,3-Trifluoropropene as Precursors of Well-Defined Fluoropolymers

Original fluorinated α,ω-diols containing 3,3,3-trifluoropropene (TFP) units were synthesized. The first step dealt with the radical telomerization of TFP with 1,6-diiodoperfluorohexane. Isolated I(TFP)RF(TFP)I diadduct was subsequently reacted with ethylene, and then a two-step hydrolysis gave rise to α,ω-diols in 25% overall yield. The other strategies dealing with the radical addition of I(TFP)RF(TFP)I onto allyl alcohol or allyl acetate led to α,ω-diols in 13% overall yield. These diols display satisfactory thermal stabilities and low Tg (ca. -60 °C).