EXPERIMENTAL PART
Materials
Vinylidene fluoride (VDF), hexafluoropropene (HFP), chlorotrifluoroethylene (CTFE) and 1,1,1,3,3-pentafluorobutane were kindly offered by Solvay S.A. (Brussels, Belgium and Tavaux, France). Perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE) was supplied by Synquest (Florida, USA). 2,5-Bis(tert-butylperoxy)-2,5-dimethylhexane, tech.
90% (Luperox 101) was provided by Aldrich Chimie (38299 Saint Quentin-Fallavier, France) and tert-butylperoxypivalate was generously offered by “La Chalonnaise des Peroxydes” (Chalons sur Marne, France). They were used as received. Pentane, acetonitrile, dimethylformamide, dimethylsulfoxyde and KOH were supplied by SDS (Peypin, France) whereas perfluorohexane provided by F2 Chemical (Preston, U.K.).
Analysis
The compositions of the co- and terpolymers (the molar contents of VDF, HFP, CTFE and PFSVE) were determined by 19F NMR spectroscopy. The 1H and 19F NMR spectra were recorded on Bruker AC 200 and AC 250 instruments, using deuterated acetone as the solvent and TMS (or CFCl3) as the references for 1H (or 19F) nuclei. Coupling constants and chemical shifts are given in Hz and ppm, respectively. The experimental conditions for 1H (or 19F) NMR spectra were the following: flip angle 90° (or 30°) , acquisition time 4.5 s (or 0.7 s) , pulse delay 2 s (or 5 s) , number of scans 16 (or 64), and a pulse width of 5 µs for 19F NMR.
Infrared spectra were recorded by a Nicolet 510P Fourrier Transformed spectrometer from KBr pellets and the intensities of the absorption bands were noted as s = strong, m = medium and w = weak, given in cm-1 (accuracy ± 2 cm-1).
Differential scanning calorimetry (DSC) measurements were conducted using a Perkin-Elmer Pyris 1 instrument connected to a micro-computer. The apparatus was calibrated with indium and n-decane. After its insertion into the DSC apparatus, the sample was initially cooled to -105 °C for 15 min. Then, the first scan was made at a heating rate of 40 °C.min-1 up to 80 °C, where it remained for 2 min. It was then cooled to -105 °C at a rate of 320 °C.min-1 and left for 10 min at that temperature before a second scan was started at a heating rate of 20 °C.min-1. Finally, another cycle was performed and a third scan at a
heating rate of 20 °C.min-1 was initiated, giving the values of Tg reported herein, taken at the half-height of the heat capacity jump of the glass transition.
Thermogravimetric analyses were performed with a Texas Instrument TGA 51-133 apparatus in air at a heating rate of 10 °C.min-1 from room temperature up to a maximum of 600 °C.
Characterization of PFSVE
PFSVE was used as received and its purity was controlled by 19F NMR spectroscopy.
19F NMR (200 MHz, acetone d6, Figure 1) δ: 45.3 (m, -SO2F, 1F, Fi) ; -79.1 (m, -OCF2CF(CF3)OCF2CF2SO2F, 2F, Fd) ; -79.8 (m, -OCF2CF(CF3)OCF2CF2SO2F, 3F, Fe) ;
-84.4 (m, -OCF2CF(CF3)OCF2CF2SO2F, 2F, Fg) ; -111.9 (m, -OCF2CF(CF3)OCF2CF2SO2F, 2F, Fh) ; -112.8 (dd, 3Jba=84.9 Hz, 3Jbc=65.8 Hz, 1F, Fb); -121.3 (ddt, 2Jac=111.6 Hz, 3Jab=84.9 Hz, 5Jad=5.7 Hz, 1F, Fa) ; -136.6 (ddt, 2Jca=111.6 Hz, 3Jcb=65.8 Hz, 4Jcd=5.7 Hz, 1F, Fc) ; -144.3 (m, -OCF2CF(CF3)OCF2CF2SO2F, 1F, Ff).
Homopolymerization and attempts of copolymerization
The batch homopolymerizations and the kinetics of copolymerizations of PFSVE were performed in thick borosilicate Carius tubes (length 130 mm, internal diameter 10 mm, thickness 2.5 mm, total volume 8 cm3). After introducing the initiator, PFSVE and the solvent under inert atmosphere, the tube was connected to a vacuum line and purged several times by evacuating and flushing with helium. After five freeze – thaw cycles, the adequate gases quantities were trapped in the tube cooled in liquid nitrogen under 20 mm Hg. To introduce the targeted gaseous monomer quantities, beforehand calibrations were made to link the gas pressure (bars) to the introduced weight (grams) (for example, a difference of pressure of 0.66 bar represents 1.00 g of VDF and for HFP a difference of pressure of 0.27 bar gives 1.00g).
The tube was sealed while immersed in liquid nitrogen and placed into a shaking oven heated to the chosen temperature for the time required. After the reaction, the tube was cooled in liquid nitrogen, opened, and their content was precipitated and analyzed by 19F and 1H NMR spectroscopy.
Copolymerization and terpolymerization in autoclave
The batch co- or terpolymerizations of VDF, HFP, or CTFE with PFSVE were performed in a 160mL Hastelloy autoclave Parr System, equipped with a manometer, a
stirring and the heating of the autoclave. The autoclave was left closed for 20 minutes and purged with 30 bars of nitrogen pressure to prevent any leakage, and degassed afterwards.
Then, a 2 mm Hg vacuum was operated for 15 min and the initiator (generally 2,5-Bis(tert- butylperoxy)-2,5-dimethylhexane, DHBP, tech. 90% ; or tertbutylperoxypivalate), PFSVE and 1,1,1,3,3-pentafluorobutane were introduced via a funnel tightly connected to the introduction valve. Next, HFP or CTFE, and VDF were respectively introduced by double weighing. The autoclave was then heated up to 134 °C for 7 hours. After reaction, the autoclave was cooled to room temperature and then put into an ice bath. After degasing the unreacted monomers, the autoclave was opened. 1,1,1,3,3-Pentafluorobutane was evaporated, the polymer was solubilized (generally in acetone) and precipitated from cold pentane. The polymer was filtrated, washed, dried over P2O5 agent at room temperature under a 20 mm Hg vacuum for 24 hours and characterized by 1H and 19F NMR spectroscopy.