Fractionation Fluoropolymers

PVDF. This polymer can contain head-to-head and tail-to-tail sequences, as illustrated in Figure 7-25. Because the 19F nucleus has a spin number of 1/2 and its natural abundance is 100%. 19F NMR spectroscopy is a powerful tool for studying fluoropolymers like PVDF. The fluorine atoms are the little yellow balls and you ll notice that one of the units in Figure 7-25 has been put in backwards, giving a head-to-head and tail-to-tail sequence. The peaks marked A, B, C and D in the spectrum of PVDF (Figure 7-26) correspond to the fluorine atoms labeled in the same way in the figure. Of course, what you would really like to know is the number fraction of VDF monomers that are incorporated backwards into the chain. This information can be obtained from the relative intensities of the bands, but to extract it we have to revisit probability theory. (Oh no the nightmare continues )... 

SCCO2 is largely used to process food (extraction or fractionation), but other applications, such as the fluoropolymer synthesis by DuPont, hydrogenation or alkylation by Thomas Swan, coatings by Union Carbide, and polyurethane processing by Crain Industries, are still in development [111]. The application of supercritical fluids (SCFs) as reaction media with homogeneous catalysts has been mainly investigated on a laboratory scale. 

Many of these properties of C02 have been known for years,2 but aside from some small specialty applications such as the extraction of caffeine from coffee beans and the fractionation of some polymeric compounds, C02-based processes have not made major inroads in industry. Over the last decade, interest in the use of C02 as a solvent has seen a great resurgence as a result of the discovery of some unique solubility properties associated with C02 that have enabled the synthesis of fluoropolymers in carbon dioxide as well as the rational design of surface-active materials that are soluble in C02. 

Properties for several TFE/PDD copolymers and PTMSP are compared in Table IV. Density and glass transition temperatures for the TFE/PDD copolymers were obtained from Buck and Resnick (44), and the density and glass transition temperature for PTMSP are from the study of Nakagawa et al.(l). Among the fluoropolymers in this table, PTFE homopolymer exhibits 5ie lowest glass transition temperature, the lowest oxygen permeability coefficient, and the lowest fractional free volume. In the polymers in Table IV, the PALS results suggests a bimodal distribution of free... 

The mineral fluorite (Cap2), also called fluorspar, is converted to hydrofluoric acid (HF) for the synthesis of refrigerants and fluoropolymers. A large fraction of the world s supply of fluorspar is controlled by China. 

The findings described in this chapter focus on fluorous copolyoxetane soft block surface modifiers. These copolyoxetane polyurethane modifiers bring about new surface properties due to surface concentration and/or phase separation of the soft block. An important theme concerns the effectiveness of a fluorous chaperone in conferring a surface function to a commodity or base polyurethane at 2 wt% or less. Thus, from one perspective, this chapter describes literally and figuratively the interface between specialty fluoropolymers and commodity polyurethanes. A significant applications niche would result if only a small fraction of the 55 billion polyurethane market (2016) [1] employed specialty fluorous modifiers. 

Here, (pi is the volume fraction of droplets with radius i ,. The volume-averaged radius can be used instead of the distribution if the polydispersity is less than 2.3. The fit to G data for a 6.5% dispersion of poly(ethylene terephthalate) in a linear fluoropolymer at 300 °C, with an average droplet radius of 5.4 /rm, is shown in Figure 14.4, where the data are plotted as the ratio of the storage modulus of the blend to that of the matrix polymer. The peak reflects the frequency regime where the interfacial dynamical response is sensitive to interfacial tension. Interfacial tension acts like an elastic stress, so the major contribution of the interface is in G . The interfacial tension of the blend estimated from standard equations is about... 

For decades, ammonium perfluorooctanoate (APFO, or C8) was an essential processing aid in the manufacture of fluoropolymers. As a polymerization aid it played a critical role in the polymerization of TFE and fluorinated comonomers used to produce PTFE, PEA (MFA), and FEP. It acted as an intermediate for the majority of fluoropolymers and was eliminated during the finishing steps. As produced solid phase fluoropolymers contained small amounts of C8 in the order of a few parts per million. Under a fraction of a percent of APFO was present in aqueous dispersion products. 

Lots of peroxides enable the curing of VDF-based fluoropolymers, but the nature of the peroxides, and the molar amount can influence many different factors such as the curing temperature and the gel fraction. 

The plain substrate material must be hydrophobized with a Teflon fluoropolymer such as polytelrafluoroelhylene (PILE) or fluorinated ethylene propylene (FEP) copolymer to create porous volume that is nonwetting to water. This leaves that fraction of pore volume open for vapor-phase transport (Le., reactant supply and water-vjpir removal). 

The structures that have evolved for ablative-mode optical discs make use of interference effects to minimize the reflectance (R) of the disc in the absence of a hole. A typical ablative-mode optical disc has the structure shown in Figure 2.51. The substrate is an optically transparent material such as polycarbonate, poly(methyl methacrylate), poly(ethylene terephthalate), or poly(vinyl chloride), topped by a subbing layer to provide an optically smooth (to within a fraction of a nanometer) surface for the recording layer. A metal reflector (typically aluminum) is then incorporated next to a transparent dielectric medium such as spin-coated poly(a-methyl styrene) or plasma-polymerized fluoropolymers. This dielectric spacing layer serves both to satisfy the quarter-wave (A/4) antireflection conditions and to insulate thermally the A1 reflector from the top absorbing layer where the information pits are created. 

Hyflon AD is an amorphous perfluorinated copolymer of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-l,3-dioxole (TTD). Compared to the situation in the Teflon AF series, the reduced intermolecular distance due to the structural change result in moderate fractional free volume of 23%. Thus, the gas permeabilities are lower than those of Teflon AF membranes, allowing the increase of permselectivities. While this fluoropolymer has the advantage of solubility in fluorinated liquid, such as Galden FIT 55 and HFE 7100, the permeation properties are affected by the kind of residual solvents as well. 

It is noticeable that the above mechanism is based on studies of fatty acid amides while other slip agents are also used for various purposes related with reduction of coefficient of fnction. Fluoropolymer additives, for example, are used to improve film extmsion in which they act in a similar manner during process as amides act in the final film. Fluoropolymer additive is also not compatible with polymer matrix. During extrusion it migrates to the surface of metal and forms film which has pronounced effect on production parameters. It reduces melt fraction, viscosity, shear rate, and gate pressure. This makes production faster and eneigy use lower. Some of these additives are developed in such a manner that they migrate only in a molten state but are immobilized within material after material solidifies. This makes them essentially absent from the film surface which in some post process operation is an important requirement. ... 

Effect of the gas composition. When operated at a constant medium bias voltage and pressure, with an increasing CF fraction in the gas mixture (series B), the fluoropolymers films produced show a continuous decrease in CF2 (Teflon type) carbon content, at the profit of the less fluorinated CF species (peaks 5 and 6). 

---