Vinylidene Fluoride Content Research Articles

Structure disorder observation of fluoropolymers composed of vinylidene fluoride and tetrafluoroethylene in supercritical CO2 using time-resolved small- and wide-angle X-ray scattering

Fluoropolymers have a growing range of applications in many industries. Neat fluoropolymers and fluorinated copolymers were prepared via the suspension polymerization method with entire mass ratio of vinylidene fluoride (VdF) and tetrafluoroethylene (TFE). Supercritical CO2 was applied as a fluid stimulus to the fluoropolymers. An increase in structural disorder was investigated using time-resolved small-angle X-ray scattering (SAXS). The SAXS change induced by the stimulus proceeded more slowly with increasing VdF ratio of the copolymer, suggesting that the higher VdF content contributes to the tolerance of microvoid formation and the corresponding onset of breakdown in the polymer material. The degree of crystallinity of the fluoropolymers was evaluated using wide-angle X-ray scattering, showing the degree of crystallinity was similar before and after the stimulus. Time-resolved and in-situ SAXS/WAXS measurements were carried out on the copolymer with a ratio of VdF:TFE = 8:2 as the copolymer having the highest VdF content studied here.

Vinylidene Fluoride-Based Polymer Network via Cross-Linking of Pendant Triethoxysilane Functionality for Potential Applications in Coatings

Vinylidene fluoride (VDF)-based copolymers bearing pendant trialkoxysilane groups for potential applications for coatings were synthesized via a free radical copolymerization of VDF with functional 2-trifluoromethyl acrylate cyclic carbonate monomer (MAF-cyCB), followed by introduction of silane pendant groups. MAF-cyCB was prepared from 2-trifluoromethacrylic acid with 70% overall yield. Radical copolymerization of VDF with MAF-cyCB initiated by tert-amyl peroxy-2-ethylhexanoate at varying [VDF]0/[MAF-cyCB]0 ratios led to several poly(VDF-co-MAF-cyCB) copolymers having different molar percentages of VDF (77–96%). The average molecular weights (Mns) reached up to 19 000 g mol–1 in fair to good yields (45–74%). Compositions and microstructures of all synthesized copolymers were achieved by 1H and 19F NMR spectroscopies. The resulting poly(VDF-co-MAF-cyCB) copolymers exhibited moderately high melting temperature (131–161 °C, with respect to the VDF content) while the degree of crystallinity, which reached u...

Poly(vinylidene fluoride) Containing Phosphonic Acid as Anticorrosion Coating for Steel.

Vinylidene fluoride (VDF)-based copolymers bearing pendant phosphonic acid function for potential application as anticorrosion coatings were synthesized via free radical copolymerization of VDF with a new phosphorus containing 2-trifluoromethacrylate monomer, (dimethoxyphosphoryl)methyl 2-(trifluoromethyl)acrylate (MAF-DMP). MAF-DMP was prepared from 2-trifluoromethacrylic acid in 60% overall yield. Radical copolymerizations of VDF with MAF-DMP initiated by tert-amyl peroxy-2-ethylhexanoate at varying ([VDF]0/[MAF-DMP]0) feed ratios led to several poly(VDF-co-MAF-DMP) copolymers having different molar percentages of VDF (79-96%) and number-average molecular weights (Mn's) up to ca. 10 000 g mol-1 in fair yields (47-53%). Determination of the composition and microstructure of all the synthesized copolymers was done by 1H and 19F NMR spectroscopies. The monomer reactivity ratios of this new VDF/MAF-DMP pair were also determined (rVDF = 0.76 ± 0.34 and rMAF-DMP = 0 at 74 °C). The resulting poly(VDF-co-MAF-DMP) copolymers exhibited high melting temperature (162-171 °C, with respect to the VDF content), and the degree of crystallinity reached up to 51%. Finally, the pendant dimethyl phosphonate ester groups of the synthesized poly(VDF-co-MAF-DMP) copolymer were quantitatively hydrolyzed, giving rise to novel phosphonic acid-functionalized PVDF (PVDF-PA). In comparison to hydrophobic poly(VDF-co-MAF-DMP) copolymers (the water contact angle, WCA, was 98°), the hydrophilic character of the PVDF-PA was found to be surprisingly rather pronounced, exhibiting low WCA (15°). Finally, steel plates coated with PVDF-PA displayed satisfactory anticorrosion properties under simulated seawater environment.

Influence of Dipolar Interactions in Ferroelectric Vinylidene Fluoride Copolymers on their Structure and Low-Temperature Molecular Mobility

Dielectric, IR spectroscopy and DSC measurements were made over a wide range of temperatures and frequencies in copolymers of vinylidene fluoride (VDF) with tetra- (TFE) and trifluoroethylene (TrFE) of different composition. Experimental results show that decrease of VDF content in VDF/TFE copolymers is accompanied by decrease of activation energy of kinetic units in the glassy state, though relaxation times of cooperative mobility in amorphous phase differ insignificantly. Substitution of TFE with TrFE in copolymers with the same VDF content increases activation energy values for the local mobility. The results of IR spectroscopy suggest that VDF/TFE copolymers with low VDF content have lower crystallinity, which may be explained by the secondary crystallization processes and absence of long isomers in planar zigzag conformation.

Synthesis and characterization of fluorinated telomers containing vinylidene fluoride and hexafluoropropene from 1,6‐diiodoperfluorohexane

AbstractThe synthesis of original fluorinated (co)telomers containing vinylidene fluoride (VDF) or VDF and hexafluoropropene (HFP) was achieved by radical telomerizations and (co)telomerizations of VDF (or VDF and HFP) in the presence of 1, 6‐diiodoperfluorohexane via a semisuspension process.tert‐Butyl peroxypivalate (TBPPi) was used as an efficient thermal initiator. The numbers of VDF and VDF/HFP base units in the (co)telomers were determined by19F and1H NMR spectroscopy. They ranged from 10 to 190 VDF base units. Fluorinated telomers of various molecular weights (1200–12,600 g/mol) were obtained by the alteration of the initial [1,6‐diiodoperfluorohexane]0/[fluoroalkenes]0and [TBPPi]0/[fluoroalkenes]0molar ratios. The thermal properties of these fluorinated (co)telomers, such as the glass‐transition temperature and melting temperature, were examined. As expected, these telomers exhibited good thermal stability. They were stable at least up to 350 °C. The compounds containing more than 30 VDF units were crystalline, whereas all those containing VDF‐co‐HFP were amorphous with elastomeric properties, whatever the number was of the fluorinated base units. The structures of I–(VDF)n–RF–(VDF)m–I and I–(HFP)x(VDF)n–RF–(VDF)m(HFP)y–I (co)telomers were obtained, and the defects of the VDF chain and the CH2CF2I and CF2CH2I functionalities were studied successfully (where RF= C6F12). The functionality in the iodine atoms was modified: the higher the VDF content in the telomers, the lower the normal end functionality (CH2CF2I) and the higher the reversed extremity (CF2CH2I). In addition, the percentage of defects increased when the number of VDF units increased. The molecular weights and molecular weight distributions of different telomers and cotelomers were also studied. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1470–1485, 2006

Original Vinylidene Fluoride-Containing Acrylic Monomers as Surface Modifiers in Photopolymerized Coatings

The syntheses of original acrylic monomers containing vinylidene fluoride (VDF) units, prepared through a four-step process starting from the telomerization of VDF with iodotrifluoromethane, are presented. By modifying the [CF3I]0/[VDF]0 initial molar ratios, different CF3(VDF)nI telomers of various molecular weights were obtained. VDF content and the microstructure of the VDF telomers were determined by 19F NMR spectroscopy, while gas chromatography confirmed the average number of VDF units in each telomer. The radical addition of these telomers onto allylic alcohol led to original oligo(VDF)-containing iodohydrins that were reduced into novel ϖ-hydroxyl-VDF telomers. These latter were acrylated, and the resulting VDF-containing macromonomers were added in low amount (0−1% w/w) into a reference telechelic hydrogenated diacrylic resin and copolymerized through the UV-curing technique. The kinetics of the photopolymerization, monitored by IR spectroscopy, and the bulk properties of the film were independent of the amount of these PVDF additives, but peculiar surface properties were shown. The low concentration of the PVDF macromonomers made the surface of the cured networks both hydrophobic and oleophobic. The surface modification, assessed by contact angles and XPS spectroscopy, concerned one side of the films. The films coated on a polar surface showed on the air side a lower surface tension than that of the substrate side, which kept the same properties as those of the pure hydrogenated resin, including a good adhesion to the substrate.

Specific heat and thermal diffusivity of vinylidene fluoride/trifluoroethylene copolymers

AbstractThe specific heat (C) and thermal diffusivity (D) of vinylidene fluoride (VDF)/trifluoroethylene copolymers with 70 and 56 mol % of VDF were measured between 200 and 390 K, and the thermal conductivity (K) was calculated from these data. C, D, and K were rather insensitive to the VDF content but varied significantly with the crystallinity. At room temperature, as the crystallinity increased from about 55 to 85%, C decreased by 17%, and D and K increased by 60 and 40%, respectively. For the copolymer with 70 mol % VDF, C exhibited a broad peak, whereas D showed an abrupt drop at the ferroelectric–paraelectric transition near 370 K on heating. The transition temperature on cooling was about 40 K below that observed in the heating run, thus revealing a large thermal hysteresis. For the copolymer with 56 mol % VDF, the transition temperature was much lower, the transition region was narrower, and the thermal hysteresis was barely observable. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3160–3166, 2003

Application of periodically modulated driving force to the transition kinetics in vinylidene fluoride/trifluoroethylene copolymers

The method of “modulated driving force” has been applied to the kinetics of ferroelectric–paraelectric transition in copolymers of vinylidene fluoride (VDF) with trifluoroethylene (TrFE). The method examines the response of transition kinetics to a periodically modulated driving force, e.g., supercooling or superheating. The response to the modulation in temperature appears in the apparent heat capacity obtained by a temperature-modulated differential scanning calorimeter. By examining the frequency dispersion and its dependence on underlying linear heating (or cooling) rate, the mean time required for the completion of transition in each crystallite and the dependence of transition rate on superheating (or supercooling) are obtainable. In VDF/TrFE copolymers, it is known that the transition behavior undergoes a drastic change from reversible transition with low VDF content to nucleation-controlled transition with higher content. Several types of compositions (VDF/TrFE=47/53, 52/48, 59/41, 65/35, 69/31 and 73/27 by mol %) have been examined experimentally with this method in terms of the crossover of transition behaviors.

Ferroelectric and antiferroelectric transitions in random copolymers of vinylidene fluoride and trifluoroethylene

Copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) containing 50–80% former undergo a ferroelectric-to-paraelectric transition and then melt. The transition entropies determined by thermal measurements are shown to be consistent with the conformational entropies of the paraelectric and molten phases that are comprised of statistical combinations of TT, TG and TG' bonds. As the VDF-content exceeds 80%, melting overtakes the transition into the paraelectric phase. TrFE-rich copolymers containing 30–50% VDF exhibit an additional phase that is shown to be antiferroelectric-like on the basis of nonlinear dielectric investigation. Ferroelectricity tends to be obscured with increasing TrFE content and disappears at PTrFE. The dependence of the transition behavior on the composition of VDF and TrFE is discussed phenomenologically. It is shown that the most essential role is played by the cohesive energy of the ferroelectric phase that decreases with increasing TrFE content due to its asymmetry and bulkiness. The resulting increase in the Gibbs energy induces appearance of the paraelectric as well as antiferroelectric phases as the VDF content is further decreased.

Computer simulation of structural changes in the ferroelectric phase transition of vinylidene fluoride–trifluoroethylene copolymers

Structural change in the ferroelectric phase transition of vinylidene fluoride (VDF)–trifluoroethylene copolymers has been simulated by using molecular dynamics (MD) technique. The force field parameters used in this simulation were those determined in the previous paper [Tashiro et al., Ferroelectrics 1995;171:281] but with some modifications to reproduce the molecular and crystal structures and the infrared/Raman spectra of PVDF crystal forms I, II, and III to a higher degree. The MD calculation was made for the crystal structures of VDF 50 and 70mol% copolymers, where the MD unit cells consisted of 16–36 chains of different monomer sequences under the three-dimensional periodic boundary condition. In the VDF 50% copolymer case, for example, the trans-to-gauche conformational change was found to occur at about 390K. The transition temperature estimated for VDF 70% copolymer was about 470K, higher than that of VDF 50% copolymer. This indicates that the copolymer with higher VDF content exhibits the transition at higher temperature, consistent with the observed results. The molecular conformation in the high-temperature phase was found to be a statistical combination of TG+, TG−, T3G+ and T3G− sequences. The population of TG+ and TG− was higher and that of T3G+ and T3G− was lower for the copolymer with higher VDF content, which was also consistent with the experimental data. The trans–gauche conformational change was done with large thermal rotation of the chains, resulting in the extinction of the electric polarization of the whole unit cell in the high-temperature phase. The ratio of the a and b axes of the basic unit cell was 1.73, characteristic of the hexagonal-type structure of the high-temperature phase.

The influence of vinylidenefluoride on the free volume of poly(chlorotrifluoroethylene)

The influence of vinylidenefluoride (three different compositions, viz. 0, 0.5 and 3.0%) on the free volume of the polymer poly(chlorotrifluoroethylene) has been investigated using the Positron Annihilation Lifetime technique. The lifetime results indicate that, with the increase in the composition of vinylidenefluoride, the average free volume size of the polymer decreases whereas their number density increases. Further, it has been observed that the glass transition temperature (Tg) of this polymer decreases with the increase in vinylidenefluoride content. The present results complement the literature report that vinylidenefluoride influences mainly the amorphous regions of poly(chlorotrifluoroethylene).

Ferroelectric Transition in Vinylidene Fluoride and Trifluoroethylene Copolymers Studied by NMR Method II. 52 and 65 mol% Vinylidene Fluoride Copolymers

NMR derivative line shapes f′(ΔH) in vinylidene fluoride (VDF)/trifluoroethylene (TrFE) copolymers with VDF contents of 52 and 65 mol% were measured as a function of the alignment angle γ between the drawn axis and magnetic field over a temperature range between 20 and 130°C. The fine structure of f′(ΔH) and the motional narrowings of the line widths in the each copolymer were investigated by comparing them with those for VDF 72 mol% copolymer. In the ferroelectric phase, f′(ΔH)’s in VDF 65 and 72 mol% copolymers consisted of three components of narrow, intermediate and broad line widths (ΔHs, ΔHm, and ΔHb), ΔHm and ΔHb which were due to the TrFE and VDF groups, respectively; f′(ΔH) in the VDF 52 mol% copolymer had two components of ΔHs, and ΔHb. The value of ΔHb was almost equal to ΔHm in 65 and 72 mol% copolymers. When VDF content decreased, the flip-flop motion of TrFE groups in the VDF 72 mol% copolymer changed into rotational motion around the chain axis. Near the Curie temperature, Tc two kinds of trans VDF group motion around the chain axis and TrFE group motion coordinate with the VDF rotational motion disappeared in the VDF 52 mol% copolymer. At the Tc, ΔHb discontinuity for each copolymer was observed, but the thermal hysteresis of ΔHb vs. temperature decreased as VDF content decreased, and was not significant in the VDF 52 mol% copolymer. These findings suggest that the ferroelectric phase transition is of the first order above VDF 65 mol%, and of the first order close to the second order for VDF 52 mol%.

Crystallization, field-induced phase transformation, thermally induced phase transition, and piezoelectric activity in P(vinylidene fluoride-TrFE) copolymers with high molar content of vinylidene fluoride

Field-induced phase transformation and thermally induced phase transition in vinylidene fluoride (VDF) and trifluoroethylene copolymers with VDF content higher than 82 mol% and their ferroelectric and piezoelectric properties have been studied by means of x-ray diffraction, DSC, D-E hysteresis, and piezoelectric resonance. It is found that copolymers with VDF content ranging from ∼82 to 90 mol% crystallize under ordinary pressure into thick lamellar single crystals composed of a mixture of α, β, and possibly γ phases. Application of a strong ac electric field transforms these mixed phase crystals into β-phase crystals completely. The β-phase crystals are ferroelectric and exhibit strong piezoelectric activity stable up to the melting temperature (160–180 °C depending on VDF content); the Curie point coincides with the melting point. Unpoled, mixed phase film has a paraelectric or rotational phase below the melting temperature, in which thick lamellar single crystals are grown extensively, whereas β-phase film prepared by mechanical drawing has no paraelectric phase below the melting point. Definite ferroelectric-to-paraelectric phase transition in P(VDF-TrFE) is inferred to occur only in thick lamellar crystals grown in the paraelectric phase. A phase diagram of P(VDF-TrFE) is described.

Effect of hydrostatic pressure on polarization reversal in copolymers of vinylidene fluoride and trifluoroethylene

Polarization reversal in copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with intermediate and higher TrFE content is characterized by two polarization current peaks at different electric field intensities. The current peaks at higher and lower field, Eh and El, correspond to polarization and depolarization processes, respectively. The temperature Tl at which El reduced to zero was related to a transition between slightly different phases. The effect of hydrostatic pressure on polarization processes was examined for the copolymers in a low pressure region of 0.1 to 100 MPa. Increasing pressure gave rise to a considerable effect on Eh and El, being similar to that in decreasing temperature. Pressure dependence of the temperature Tl was as large as about 0.3 KMPa-l. This work presents another feature of the polarization processes in these copolymers which are different from those in high VDF content copolymers.

The dielectric and piezoelectric properties of vinylidene fluoride-trifluoroethylene copolymers

The dielectric and piezoelectric properties of vinylidene fluoride (VDF) -trifluoroethylene (TrFE) copolymers with molar compositions of 56:44, 70:30 and 80:20 VDF:TrFE have been studied. Ferroelectric to paraelectric phase transitions have been observed by measurement of dielectric constant as a function of temperature. The transition temperature increases from 70°C to 121°C with increasing VDF content. Optimisation of piezoelectric coefficient with respect to poling field, on thin (30-80 μm) solvent cast films, produces d31 = d32 values of 21 pCN-1 for the 56:44 VDF:TrFE copolymer, 17 pCN-1 for the 70:30 and 10 pCN-1 for the 80:20. The effect on the piezoelectric properties of ageing the films at 70°C for periods of up to 24 hours are reported and a comparison made between the properties of solvent-cast and pressed films. The potential of VDF:TrFE copolymers for piezoelectric applications is discussed.

Curie Transition in Poled and Unpoled Copolymer of Vinylidene Fluoride and Tetrafluoroethylene

Copolymers of vinylidene fluoride (VDF) and tetrafluoroethylene (TeFE) with TeFE content ranging from 17.8 to 30.7 mol% were studied by thermal, dynamic mechanical, and thermally stimulated current measurements. Below the melting point, a small endotherm was observed in differential thermal analysis. Corresponding to the endotherm, a crystalline relaxation, designated as Tt, was observed by mechanical measurements. It was inferred that the endotherm and the Tt mechanical relaxation were due to the Curie transition. The Curie points of these copolymers were about 50 K lower than those of VDF-trifluoroethylene (TrFE) copolymers with the same VDF content. In X-ray measurements, it was confirmed that these copolymers took the all-trans crystal structure similar to that of PVDF form I of which the crystal lattice expanded in a- and b-axis directions and was disordered in the c-axis repeat in comparison with that for VDF-TrFE copolymers. The Curie temperature for poled samples increased by about 50 K. The poling procedure made the crystal lattice compact in a- and b-axis directions and the c-axis repeat regular; this seems to be related to the considerable increase in the Curie temperature.

Transition Behavior and Dielectric Properties in Trifluoroethylene and Vinylidene Fluoride Copolymers

The transition behavior and dielectric properties of trifluoroethylene (TrFE)–vinylidene fluoride (VDF) copolymers were studied. The DSC and X-ray diffraction measurements indicated that the conformation of the polymers was in a crystalline state throughout the entire polymer composition, and crystallized isomorphically. In the thermal expansion measurement of the 56:44 TrFE–VDF copolymer, two breaks were observed, indicating two glass-to-rubber transitions. These two transitions were also observed in a mechanical relaxation study with peaks at 40°C (designated as β1) and −20°C (designated as β2), measured at 35 Hz. The β1-transition was tentatively assigned to the micro-Brownian motion of the main chain in the amorphous phase rich in TrFE-units; the β2-transition was assigned to the micro-Brownian motion of the main chain in the amorphous phase, rich in VDF-units. It was also found that the dielectric constant e′ of TrFE–VDF copolymer took on a maximum at 55 mol% VDF content. The numerical value of e′ was 15 (at 1 kHz and at 22°C) and about 1.7 times larger than those of poly(trifluoroethylene) and poly(vinylidene fluoride) homopolymers.