Polytetrafluoroethylene Phases

A need for single-phase polymers in some applications, e.g., polytetrafluoroethylene, VHMWPE, light-sensitive polymers, etc. 

Some authors have suggested the use of fluorene polymers for this kind of chromatography. Fluorinated polymers have attracted attention due to their unique adsorption properties. Polytetrafluoroethylene (PTFE) is antiadhesive, thus adsorption of hydrophobic as well as hydrophilic molecules is low. Such adsorbents possess extremely low adsorption activity and nonspecific sorption towards many compounds [109 111]. Fluorene polymers as sorbents were first suggested by Hjerten [112] in 1978 and were tested by desalting and concentration of tRN A [113]. Recently Williams et al. [114] presented a new fluorocarbon sorbent (Poly F Column, Du Pont, USA) for reversed-phase HPLC of peptides and proteins. The sorbent has 20 pm in diameter particles (pore size 30 nm, specific surface area 5 m2/g) and withstands pressure of eluent up to 135 bar. There is no limitation of pH range, however, low specific area and capacity (1.1 mg tRNA/g) and relatively low limits of working pressure do not allow the use of this sorbent for preparative chromatography. 

Oil-wetting systems can be modeled by replacing the glass plate with a plate of polytetrafluoroethylene (PTFE), as shown in the hexadecane/water/PTFE system in Figure 4. At the hexadecane/water interface the water phase did not wet the PTFE surface, the contact angle was thus greater than 90° and the tension decreased. The peak... 

When a glass plate which is heated e.g. at 130°C is rubbed with a polytetrafluoroethylene (PTFE) briquette, a highly oriented thin film (2— 100 nm thick) of PTFE can be made on the plate such a film is termed a friction-transfer layer [24]. This method is applicable to make thin oriented layers of other polymers. Various kinds of organic compormds can be oriented on the PTFE friction-transfer layer from vapor phase, from solutions and from the melts [24]. 

V.N. Vasilets, G. Hermel, U. Konig, C. Werner, M. Muller, F. Simon, K. Grundke, Y. Ikada, H.J. Jacobasch, Microw/ave CO2 plasma-initiated vapour phase graft polymerization of acrylic acid onto polytetrafluoroethylene for immobilization of human thrombomodulin. Biomaterials 18 (1997) 1139-1145. 

The mobile phase is a solution of methanol acetonitrile water (53 23 24) containing 30 mM ammonium acetate adjusted to pH 5.6 with acetic acid this solution is filtered through polytetrafluoroethylene 0.45-pm filters. 

Polytetrafluoroethylene (PTFE) is an attractive model substance for understanding the relationships between structure and properties among crystalline polymers. The crystallinity of PTFE (based on X-ray data) can be controlled by solidification and heat treatments. The crystals are large and one is relieved of the complexity of a spherulitic superstructure because, with rare exceptions, spherulites are absent from PTFE. What is present are lamellar crystals (XL) and a noncrystalline phase (NXL) both of which have important effects on mechanical behavior. 

PTFE polytetrafluoroethylene PUFA polyunsaturated fatty acid PV peroxide value PVDF polyvinylidene difluoride PVP polyvinylpyrrolidone PVPP polyvinylpolypyrolidone RAS retronasal aroma stimulator RDA recommended dietary allowance RF radio frequency RFI relative fluorescence intensity RI retention index RNU relative nitrogen utilization ROESY rotational nuclear Overhauser enhancement spectroscopy RP-HPLC reversed-phase HPLC RPER relative protein efficiency ratio RS resistant starch RT retention time RVP relative vapor pressure S sieman (unit of conductance)... 

Esveld et a/.81,82 developed a continuous dry media reactor (CDMR) for pilot-scale applications. It consisted of a multi-modal tunnel microwave cavity operating at a frequency of 2.45 GHz with a power range from 0 to 6 kW irradiated on a surface of 0.6 m2. Temperatures of up to 250°C were achieved. A web conveyor travelling at 17 cm min-1 transported the solid-phase reaction mixture to the oven in low, open Pyrex supports closely packed on a polytetrafluoroethylene (PTFE)-coated glass fibre. An open flat bed process was employed to facilitate easy evaporation. 

Tanaka, H. and Takemura, T. Studies on the high-pressure phases of polyethylene and polytetrafluoroethylene by Raman spectroscopy. Polymer J. 12, 355 (1980)... 

Nafion (17) is a perfluorinated polymer related to teflon (polytetrafluoroethylene). An electrode is conveniently coated by allowing an ethanolic solution of the polymer to evaporate. The film produced is stable, rather more so in fact than other polymer films, e.g. polyvinylpyridine (see Section 57.3.2.2). At the microscopic level the polymer separates into two phases, the bulk polymer and the lower density ionic cluster phase. Diffusion of ions can occur quite freely for example, the diffusion coefficient of Na+ in Nafion (MW 1200) is only slightly less than in water.44... 

Marx and Dole and Miyake have presented descriptive models for the 19° C transition in terms of order-disorder theories. Studies of transitions at high pressure in polytetrafluoroethylene have been reported by Bridgman, Weir (1953), and Beecroft and Swenson. The phase diagram in Fig. 7 shows that in addition to the two crystalline phases which are separated by the 19° transition at atmospheric pressure there is a third modification at high pressures. The triple point has been... 

Fig. 7. Phase diagram for polytetrafluoroethylene. (Low temperature transitions according to Beecroft and Swenson, melting according to McGeer and Duus)...

In this paper we examine electron diffraction fiber patterns of the homopolymer polytetrafluoroethylene (-CF2 CF2-)n PTFE, in which the resolution is sufficient to yield much more accurate values of layer line heights than were available from the previous x-ray diffraction experiments (1) on the crystal structure of Phase II, the phase below the 19°C transition (2). On the basis of x-ray data, the molecule was assigned the conformation 13/6 or thirteen CF2 motifs regularly spaced along six turns of the helix. This is equivalent to a 132 screw axis. The relationship between the molecular conformation and the helical symmetry has been studied by Clark and Muus (3) and is illustrated in Figure 1. The electron diffraction data of high resolution enabled us to determine if this unusual 13-fold symmetry was exact or an approximation of the true symmetry. We have also... 

The conformation of the polytetrafluoroethylene molecule in the low temperature form (Phase II) has been determined to be 2.159 CF2 units per turn of the helix within the limits of experimental error. This conformation is slightly untwisted from the previously assigned 13/6 = 2.167 value but is substantially different from that for the 25°C form (Phase IV) in which the conformation is 15/7 = 2.143. By comparison, the planar zig-zag is 2/1 = 2.000. 

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