Hexafluoropropylene Content Research Articles

Expanding Fluorinated‐Energetic Feedstock for Fused Deposition Modeling

To probe reaction kinetics and polymer decomposition, energetic filaments composed of aluminum (Al) and poly(vinylidene fluoride) (PVDF) with varying hexafluoropropylene (HFP) content are tested for processability and combustion characteristics. Rheological and crystallization findings indicate that the Al‐binder interfacial interactions are disrupted by HFP content. Thermal analysis shows that fuel consumption scales with Al particle size due to the diffusion‐driven Al‐fluoropolymer reaction regardless of HFP concentration. Char yield analysis shows that more solid product is retained in samples with smaller particle diameters, which further reflects the diffusive nature of both Al‐PVDF and Al‐P(VDF‐HFP) reactions. Burn rates reveal two competing mechanisms for reaction efficiency: 1) accelerated binder decomposition through Al‐PVDF interactions and 2) more energetic fluorination due to higher fluorine content in the P(VDF‐HFP) binders. Finally, powder X‐ray diffraction (PXRD) patterns show that AlF3 is the primary product from self‐propagating burns. However, in larger Al particle sizes, filaments are unable to burn completely and result in high levels of Al2O3 and Al4C3 formation, which indicates that these binders are not amenable with low surface area, metallic fuels. These findings aim to improve fluorinated feedstock selection for potential binder candidates in energetic additive manufacturing (AM).

Synthesis and characterization of poly(trifluoroethylene-co-hexafluoropropylene) and the optical properties of its thin films

Copolymers of trifluoroethylene (TrFE) and hexafluoropropylene (HFP) were synthesized and characterized by various instrumental techniques. The maximum incorporation of HFP was 19.6 mol%. It was found that the reactivity ratios of TrFE and HFP were r TrFE =4.12 and r HFP ≈0, respectively, by applying Mayo-Lewis method. It was also found that the incorporation of HFP in copolymer chain influenced thermal properties. As increasing HFP content in copolymers, the melting temperature and crystallinity of copolymers were decreased and the glass transition temperature of copolymers gradually shifted to low temperature. Reduced crystallinity of copolymers was helpful to prepare coating layers having much even surface. Compared with coating layer prepared from TrFE homopolymer, the surface roughness was decreased and light transmittance through the coating layer increased when the copolymers of TrFE and HFP were used. This tendency was more appreciable as increasing HFP content in the copolymers.

Composition heterogeneity of tetrafluoroethylene-hexafluoropropylene random copolymers characterized by successive self-nucleation and annealing

In the present work, successive self-nucleation and annealing (SSA) was applied to a series of tetrafluoroethylene-hexafluoropropylene random copolymers (FEPs). Multiple melting peaks were observed for all FEP samples after SSA thermal treatment. The lamellar crystal thicknesses were calculated from the melting temperatures, and the mass percentages of the crystals of specific thickness were obtained from the areas of the melting peaks. As a result, distributions of the lamellar thickness, which can be correlated to the composition distribution, were determined. It was found that the composition distribution of the FEP samples tended to become more heterogeneous as the content of hexafluoropropylene (HFP) comonomer increases. Samples with the same HFP content might also have different composition distributions.

비닐리덴 플루오라이드와 헥사플루오르프로필렌 공중합체의 합성

Polyvinylidene fluoride (PVDF) and its copolymer with hexafluoropropylene (HFP) were successfully prepared from free radical solution polymerizations using diisopropyl peroxidicarbonate (DIPPDC) in the presence of 1,1,2-trichlorotrifluoroethane (R-113). The reactivity ratios of VDF and HFP were estimated as and . This result indicates that HFP cannot undergo self propagation. The weight-average molecular weight and molecular weight distribution of copolymers were found to decrease with increasing HFP content. The melting temperature of copolymers linearly decreased with the increase of HFP content because of the introduction of HFP. Moreover, no melting peak was observed for the copolymers with high HFP content. The glass transition temperature of copolymers gradually increased with the increase of HFP content due to the restricted flexibility of the polymer chains.

Influence of third monomer on the crystal phase transition behavior of ethylene–tetrafluoroethylene copolymer

Crystal phase transition between the low- and high-temperature phases has been investigated for ethylene (E)–tetrafluoroethylene (TFE) alternating copolymer (ETFE) containing the third monomeric species by the temperature dependent measurements of wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) and differential scanning calorimetry. Nonafluoro-1-hexene (NFH) and hexafluoropropylene (HFP) were chosen as the third monomers, where they are different in the side-branch length, –(CF2)3CF3 and –CF3, respectively. In the case of E/TFE/NFH copolymer (ET–C4F9), the crystal phase transition temperature of the original ETFE two-components copolymer was not very much affected by the existence of NFH in the range of NFH content from 0.7 to 3mol%. Contrarily, the crystal phase transition temperature of E/TFE/HFP copolymer (ET–CF3) was found to decrease drastically with increasing HFP content. The melting temperature and the higher-order structure were also affected sensitively depending on the HFP content. This difference in phase transition behavior between ET–C4F9 and ET–CF3 copolymers is reasonably interpreted as follows: the short side groups (–CF3) of HFP monomeric unit are included in the crystal lattice of E/TFE chains and the unit cell is expanded gradually with an increment of the HFP content, resulting in the decrease in phase transition point because of easier thermal motion of the chains. On the other hand, the long side groups [–(CF2)3CF3] of NFH monomeric units are excluded out of the crystal lattice and located on the lamellar surfaces or in the amorphous region and do not affect very much the phase transition temperature even when the NFH content is increased. In association with such a change in crystal structure, the long period of stacked lamellar structure was found to decrease remarkably in the case of NFH, whereas it does not change very much for HFP, consistent with the interpretation of the above-mentioned WAXD data.

Structure formation in crystallizing ferroelectric polymers

The structure of ferroelectric copolymers of vinylidene fluoride with hexafluoropropylene is investigated using wide-angle x-ray diffraction. It is shown that the crystallization of extruded films of vinylidene fluoride-hexafluoropropylene copolymers brings about the formation of the nonpolar α modification and, possibly, the polar αp modification. An increase in the hexafluoropropylene content in the copolymer leads to a decrease in the degree of perfection of the α (αp) phase, on the one hand, and a reduction of its volume fraction, on the other hand.

High temperature stable lithium-ion polymer battery

The electrochemical performance of polymer lithium-ion batteries was studied as a function of the hexafluoro propylene (HFP) content in the PVDF–HFP copolymers used as electrode binders and separator membranes. The HFP content in electrode binders was found to have a significant impact on the cycle life performance at elevated temperatures. Best results were achieved with a 5% HFP level, where good cycle life was demonstrated at 60°C, combined with good rate capabilities and low temperature performance. In contrast to electrode binders, the HFP content in separator membranes was found to have no significant impact on cell performance.

Copolymerization of hexafluoropropylene and tetrafluoroethylene: Effect on chain conformation and crystal structure

A series of new copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) containing up to 50 mol % of the hexafluoropropylene comonomer have been investigated with respect to chain conformation and crystal structure using wide-angle X-ray diffraction (WAXD). Increasing HFP content leads to significant departures from the highly ordered crystalline structure of the homopolymer PTFE; the helical conformation of the chain relaxes and untwists to accommodate the larger CF3 pendant group in the HFP unit. Simultaneously the lateral hexagonal packing of the helices becomes less ordered and the a-dimension of the hexagonal cell increases. The above effects are progressive with increasing HFP content. At 50 mol % HFP incorporation the structure is a disordered crystalline phase. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2811–2819, 1998

Copolymerization of hexafluoropropylene and tetrafluoroethylene: Effect on chain conformation and crystal structure

A series of new copolymers of tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) containing up to 50 mol % of the hexafluoropropylene comonomer have been investigated with respect to chain conformation and crystal structure using wide-angle X-ray diffraction (WAXD). Increasing HFP content leads to significant departures from the highly ordered crystalline structure of the homopolymer PTFE; the helical conformation of the chain relaxes and untwists to accommodate the larger CF3 pendant group in the HFP unit. Simultaneously the lateral hexagonal packing of the helices becomes less ordered and the a-dimension of the hexagonal cell increases. The above effects are progressive with increasing HFP content. At 50 mol % HFP incorporation the structure is a disordered crystalline phase. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2811–2819, 1998

Supercritical Fractionation of A Perfluorinated Copolymer

A perfluorinated copolymer, poly(tetrafluoroethylene-co-19, 3 mol % hexafluoropropylene), is fractionated using supercritical SF6. The fractionations arc performed isothermally at 163°C using an increasing pressure profile to obtain gram-sized fractions that have molecular weight distributions that are narrower than that of the parent copolymer. The fractionation pressure is increased in increments of 34 bar from 276 to 683 bar. The parent material and the fractions are characterized using SEC and FTTR spectroscopy. The first seven samples, eluting between 276 and 552 bar, show a trend of increased molecular weight of the fraction with increasing fractionation pressure. Above 552 bar, the molecular weight of the remaining fractions decreases with increasing fractionation pressure. Although these last fractions do not differ in hexafluoropropylene content, they do differ in the type and concentration of their end groups. In particular, the fractions that eluted at pressures greater than 552 bar contain increasing amounts of carboxylic acid end groups. The strong hydrogen-bonding interactions of these end groups prevent oligomers with acid ends from eluting from the column at lower pressures, which was expected due to their lower molecular weight.

Ferroelectric Behavior of Thin Films of Vinylidene Fluoride/Trifluoroethylene/Hexafluoropropylene Copolymer

Ferroelectricity in vinylidene fluoride (VDF), trifluoroethylene (TrFE) and hexafluoropropylene (HFP) copolymers (P(VDF/TrFE/HFP)) with a low HFP content (lower than 11 mol%) has been investigated primarily through switching measurements using P(VDF/TrFE) as a comparison. Switching phenomena as a result of ultimately 180° rotations of individual molecular chains around their axes in crystalline regions were observed in P(VDF/TrFE/HFP) with an HFP content lower than 2.5 mol%. With increasing HFP content in P(VDF/TrFE/ HFP), the amount of reversed polarization decreases, and the dielectric permittivity at the Curie point becomes smaller. However, the switching times have very low dependence on the HFP content of P(VDF/TrFE/HFP). These results suggest that noncrystalline regions in P(VDF/TrFE/HFP) are similar to those in P(VDF/TrFE), and the disorder in crystalline regions of P(VDF/TrFE/HFP) increases compared to that in crystalline regions of P(VDF/TrFE).

Radiation‐induced emulsion polymerization of ethylene. V. Copolymerization of ethylene with hexafluoropropylene

AbstractThe emulsion copolymerization of ethylene with hexafluoropropylene was studied by using 60Co γ‐radiation as the initiator. The apparent rate of copolymerization is proportional to the 1.6 power of ethylene fugacity. The activation volume was calculated from the pressure dependence of the apparent rate constant of copolymerization and was −30 ml/mole, which is smaller than the value reported by Wada et al. for ethylene polymerization in tert‐butyl alcohol. The copolymer produced had a broad composition from ethylene‐rich to alternative. As expected, the former was a crystalline, polyethylenelike copolymer, but the latter was an amorphous and rubberlike copolymer. The glass transition temperature of the copolymers increased with an increase in hexafluoropropylene content. The thermal degradation temperature in an atmosphere of nitrogen decreased slightly with introduction of hexafluoropropylene in polyethylene, but the thermal degradation behavior in air was complicated by the introduction of hexafluoropropylene.

Relaxations in Copolymers of Tetrafluoroethylene and Hexafluoropropylene

The modulus and internal friction of copolymers of tetrafluoroethylene and hexafluoropropylene (HFP) were measured with longitudinal waves at a frequency of 12 Mc between −80° and 260°C. The dielectric dissipation factor was measured at 0.1, 1.0, 10, and 100 kc between −180° and 200°C. Samples included copolymers with compositions ranging from pure polytetrafluoroethylene to pure polyhexafluoropropylene. A relaxation at −10°C (12 Mc) in polytetrafluoroethylene shifts to higher temperatures with increasing HFP content. Data suggest that 5 to 13 main-chain carbon atoms are involved, a size consistent with assigning the relaxation to motions of a small point defect in the crystal lattice. Molecular models indicate that the effects of these defects are reduced by perfluoromethyl groups which enter the lattice as another kind of point defect. Dielectric and mechanical relaxation temperatures agree approximately and yield the same activation parameters. These parameters exhibit no significant variation with HFP content and follow a relation which applies to activated processes in inorganic solids. The relation also obtains for a relaxation at 197°C (12 Mc) in polytetrafluoroethylene. This relaxation shifts to lower temperatures and the activation enthalpy decreases with increasing HFP content. Dielectric data do not exhibit the relaxation, and heating polytetrafluoroethylene near the melting point does not introduce sufficient polar groups to alter this result. Another relaxation observed below −150°C in the dielectric but not in the ultrasonic data is independent of polymer density and HFP content.