Ethylene-tetrafluoroethylene, crystalline

Finally, in this section, the simple Hartmann-Hahn cross polarization experiment, and in particular, the JH-19F CP build up curve was used to determine the residual JH-19F dipolar coupling constant due to motion in an ethylene/tetrafluoroethylene co-polymer.31 This curve for the crystalline... 

Poly(Ethylene-Tetrafluoroethylene) n (PE-TFE) A crystalline resin in which the proportion of ethylene to tetrafluoroethylene (E/TFE) may range, for the best combination of properties, between 2 3 and 3 2, modified with a vinyl copolymer for better toughness. It is stronger than either low-density polyethylene or polytetrafluoroethylene, has good electrical properties, high Izod-impact strength, and plastic memory that makes it useful for heat-shrinkable packaging. 

The highly crystalline fluoropolymers include fluorinated ethylene polyethylene, perfluoroalkoxyethylene, polychlorotrifluoroethylene and ethylene-tetrafluoroethylene co-polymer but PTFE is perhaps the most widely used and certainly best known as Teflon in non-stick cookware. 

The equimolar copolymer of ethylene and tetrafluoroethylene is isomeric with poly(vinyhdene fluoride) but has a higher melting point (16,17) and a lower dielectric loss (18,19) (see Fluorine compounds, organic-poly(VINYLIDENE fluoride)). A copolymer with the degree of alternation of about 0.88 was used to study the stmcture (20). Its unit cell was determined by x-ray diffraction. Despite irregularities in the chain stmcture and low crystallinity, a unit cell and stmcture was derived that gave a calculated crystalline density of 1.9 g/cm. The unit cell is befleved to be orthorhombic or monoclinic (a = 0.96 nm, b = 0.925 nm, c = 0.50 nm 7 = 96%. 

Because of the geometric regularity present, gutta-percha (/ra/w-polyi-soprene) and stretched NR from Hevea brasitiensis (c/s-polyisoprene) are crystalline. Random copolymers are usually amorphous, but some may be crystalline if the comonomers, such as ethylene and tetrafluoroethylene, are similar in size. Block copolymers may have crystalline domains if either of the com-... 

Poly(ethylene-co-tetrafluoroethylene) does not reveal a crystalline transition and could not be extruded in the solid state ... 

Copolymers of tetrafluoroethylene and ethylene are highly crystalline and fragile at elevated temperatures and are modified by a third monomer. Production of ETFE terpolymers having improved high temperature mechanical (especially tensile) properties has been demonstrated. They comprise of 40-60 mol% ethylene, 40-60 mol% tetrafluoroethylene, and a small amount of a polymerizable vinyl termonomer, such as perfluoroisobutylene, perfluoropropyl vinyl ether, and hexafluoropropylene. 

Bursts of pulses with a predefined number down to N= 1 were selected with a pulse picker. The focusing conditions were already described in connection with Fig. 10. Various polymer foils (250 pm thick) like polyimide (PI), polycarbonate (PC), poly(ethylene terephthalate) (PET, amorphous and crystalline), poly(tetrafluoroethylene) (PTFE), and poly(methyl methacrylate) (PMMA) were investigated (all from Goodfellow Cambridge Ltd, Huntington). These are listed together with relevant physicochemical properties in Table 1. 

The irradiation of poly(vinyhdene fluoride) (PVDF) brings about Httle enhancement in the crystallinity for irradiation doses of about 100 kGy similar to poly(ethylene-a/f-tetrafluoroethylene) (ETFE). However, beyond 100 kGy, ETFE shows significant loss in the crystallinity but PVDF remains almost unchanged [34]. 

Hexafluoropropylene is produced by the pyrolysis of tetrafluoro-ethylene. The copolymer of hexafluoropropylene with tetrafluoroethylene is a medium-grade thermoplast with a crystallinity of 40-50% (drawn) to 50-70 % (annealed). The copolymer has similar mechanical and chemical properties to poly(tetrafluoroethylene), but can be molded and extruded. 

Acrylonitrile Butadiene Styrene Acrylonitrile Styrene Acrylate Cyclic Olefin Copolymer Polyethylene Chlorotrifluoroethylene Polyethylene Tetrafluoroethylene Ethylene Vinyl Acetate Fluorinated Ethylene Propylene High Density Polyethylene High Performance Polyamide Liquid Crystalline Polymer Low Density Polyethylene Linear Low Density Polyethylene Medium Density Polyethylene Polyamide (Nylon)... 

The relaxation behavior of partially crystalline systems is complex and different from amorphous polymers. Observations give the general impression that, in comparison to amorphous systems, partially crystalline samples are much less uniform in behavior. Many of the systems exhibit peculiarities and these can dominate the viscoelastic properties. This is not the place to explore this large field in the necessary depth, which would mean we would have to discuss separately the mechanical behavior of polyethylene, poly(ethylene terephtha-late), polypropylene, it-polystyrene, poly(tetrafluoroethylene) etc. What can be done for illustration is to pick out one instructive example and we select polyethylene. 

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