Polyethylene fluorination

The volatility of stabilizers from polymers is affected by both the properties and structures of the stabilizer and polymer and the external physical conditions of the experiment. Moreover, volatility is governed by diffusion of stabilizer in the polymer since volatilization causes a concentration gradient near the surface and subsequent additive loss from the surface must be replaced by diffusion from the bulk. It was found, for example, that the rate of evaporation of phenyl-2-naphthyl-amine from polymers decreases in the series polyethylene > fluorinated rubber > polybutadiene > butadiene styrene rubber > butadiene acrylonitrile rubber and this parallels the solubility of the naphthylamine in these polymers. The polarity of these polymers increases in the same order which is reflected in a decrease in diffusion coefficient and increasing intermolecular interaction in the polymer-stabilizer system. 

Carbon-fluorine bonds are quite strong (slightly stronger than C—H bonds) and like polyethylene Teflon is a very stable inert material We are all familiar with the most characteristic property of Teflon its nonstick surface This can be understood by com paring Teflon and polyethylene The high electronegativity of fluorine makes C—P bonds less polarizable than C—H bonds causing the dispersion forces m Teflon to be less than those m polyethylene Thus the surface of Teflon is even less sticky than the already slick surface of polyethylene... 

An important newer use of fluorine is in the preparation of a polymer surface for adhesives (qv) or coatings (qv). In this apphcation the surfaces of a variety of polymers, eg, EPDM mbber, polyethylene—vinyl acetate foams, and mbber tine scrap, that are difficult or impossible to prepare by other methods are easily and quickly treated. Fluorine surface preparation, unlike wet-chemical surface treatment, does not generate large amounts of hazardous wastes and has been demonstrated to be much more effective than plasma or corona surface treatments. Figure 5 details the commercially available equipment for surface treating plastic components. Equipment to continuously treat fabrics, films, sheet foams, and other web materials is also available. 

Titanium tetrafluoride may be prepared by the action of elemental fluorine on titanium metal at 250°C (5) or on Ti02 at 350°C. The most economical and convenient method is the action of Hquid anhydrous HF on commercially available titanium tetrachloride in Teflon or Kynar containers. Polyethylene reacts with TiCl and turns dark upon prolonged exposure. The excess of HF used is boiled off to remove residual chloride present in the intermediates. 

In 1954 the surface fluorination of polyethylene sheets by using a soHd CO2 cooled heat sink was patented (44). Later patents covered the fluorination of PVC (45) and polyethylene bottles (46). Studies of surface fluorination of polymer films have been reported (47). The fluorination of polyethylene powder was described (48) as a fiery intense reaction, which was finally controlled by dilution with an inert gas at reduced pressures. Direct fluorination of polymers was achieved in 1970 (8,49). More recently, surface fluorinations of poly(vinyl fluoride), polycarbonates, polystyrene, and poly(methyl methacrylate), and the surface fluorination of containers have been described (50,51). Partially fluorinated poly(ethylene terephthalate) and polyamides such as nylon have excellent soil release properties as well as high wettabiUty (52,53). The most advanced direct fluorination technology in the area of single-compound synthesis and synthesis of high performance fluids is currently practiced by 3M Co. of St. Paul, Minnesota, and by Exfluor Research Corp. of Austin, Texas. 

Chemical Hazards. Chemical manufacturers and employees contend with various ha2ards inherent ia productioa of evea commonplace materials. For example, some catalysts used ia the manufacture of polyethylene (see Olefin polymers) ignite when exposed to air or explode if allowed to become too warm the basic ingredient ia fluorocarboa polymers, eg, Tefloa (see Fluorine compounds, organic), can become violently self-reactive if overheated or contaminated with caustic substances (45,46) one of the raw materials for the manufacture of acryflc fibers (see Fibers, acrylic) is the highly toxic hydrogen cyanide (see Cyanides). 

The size of the group attached to the main chain carbon atom can influence the glass transition point. For example, in polytetrafluoroethylene, which differs from polyethylene in having fluorine instead of hydrogen atoms attached to the backbone, the size of the fluorine atoms requires the molecule to take up a twisted zigzag configuration with the fluorine atoms packed tightly around the chain. In this case steric factors affect the inherent flexibility of the chain. 

Chlorinated polyether used in temperatures up to 120°C in forms of coatings, extruded pipe and sheet linings is an intermediate between the low-cost commodity polymers such as PVC and polyethylene, and fluorinated polymers [61 ]. 

Deep fluonnation using the La-Mar technique was carried out on polymers such as polyethylene and polypropylene [M], on polyethers [19, 20, 21], and on polyesters subsequently treated with sulfur Cetrafluoride [22] Deep fluorinations carried out under conditions producing limited fragmentation produced oligomeric perlluoropolyethers from powdered polyethylene oxide [23] Deep fluorinations earned out in the limited presence of molecular oxygen result in the conversion of... 

Polyethylene glycol (molecular weight, 300-6(W) can aid in the displacement of activated halogen by fluorine. Propionyl chloride is converted to propionyl fluoride with potassium fluoride and polyethylene glycol in acetonitrile [63] Treatment of benzyl chloride with a mixture of potassium fluoride and potassium iodide for 5 h in acetonitrile containing polyethylene glycol 200 gives benzyl fluoride in 62% yield [64],... 

Tetrasubstituted phosphonium halides are just as effective as their ammonium counterparts. A combination of tetraphenylphosphonium bromide and either 18-crown-6 or polyethylene glycol dimethyl ether with spray-dried potassium fluoride converts 4-chlorobenzaldehyde to 4-fluorobenzaldehyde in 74% yield [67] In addition, the halogen of a primary alkyl chloride or bromide is easily displaced by fluorine in aqueous saturated potassium fluoride and a catalytic amount of hexadecyltributylphosphonium bromide [68] (Table 7 Procedure 4, p 194)... 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

Tetrafluoromethane plasma modified polyethylenes indicate two mechanisms degradation and fluorination. These reactions are competitive and parallel [42]. 

By permission, Norton Chemical Process Products Corp., Bull. SI-72 and Bull. PTP-1 other manufacturer s data are equivalent, f Also available in polypropylene (including glass reinforced) high density polyethylene, rigid PVC, fluorinated vinyls. 

A large range of man-made polymeric materials is available, from polyethylene, which is attacked by most organic chemicals, to fluorinated products such as polytetrafluoro-ethylene and polyethyletherketones, which have exceptional resistance to virtually all chemicals. All polymers have their own adhesive, welding and fabrication limitations which must be taken into account in the design of the coated item. These materials can also be used in solid form. 

Thermogravimetric data indicate that the structure of a polymer affects stability in a neutral environment (HI). A polymer such as Teflon, with carbon-carbon bonds which are (by comparison) easily broken, and with strong carbon-fluorine bonds, is quite stable thermally. However, polyethylene, also with carbon-carbon bonds but containing carbon-hydrogen bonds which are broken relatively easily in comparison with the carbon-fluorine bond, is less stable than Teflon. In turn, polyethylene is more stable than polypropylene. This difference in stability is probably caused by tertiary carbon-hydrogen bonds in polypropylene. Polypropylene is more stable than polyisobutylene or polystyrene, which decompose principally by unzipping mechanism. 

Dynamar Polymer Processing Additive Technical Information, Parr Bomb Analytical Method for Determining Total Organic Fluorine Concentration in Polyethylene, Dyneon, Oakdale, MN (n.d.). 

Many polymer items are designed specifically to make contact with other materials. Where surface contact is concerned, two key properties are coefficient of friction and abrasion resistance. Polymers used in such applications include ultra high molecular weight polyethylene, polyacctal, fluorinated polymers, and natural and synthetic rubbers. Examples that we routinely come across include furniture upholstery, bushings and gears in office equipment, and bicycle tires. Industrial uses include the outer cover of electrical cables, and pipes that convey abrasive liquids such as slurries and powders. 

Various polymeric materials were tested statically with both gaseous and liquefied mixtures of fluorine and oxygen containing from 50 to 100% of the former. The materials which burned or reacted violently were phenol-formaldehyde resins (Bakelite) polyacrylonitrile-butadiene (Buna N) polyamides (Nylon) polychloroprene (Neoprene) polyethylene polytriflu-oropropylmethylsiloxane (LS63) polyvinyl chloride-vinyl acetate (Tygan) polyvinylidene fluoride-hexafluoropropylene (Viton) polyurethane foam. Under dynamic conditions of flow and pressure, the more resistant materials which binned were chlorinated polyethylenes, polymethyl methacrylate (Perspex) polytetraflu-oroethylene (Teflon). 

These moment studies have been performed on polymer systems such as polyethylene (or on penetrants in polymer systems) in which the interacting spins (protons or fluorines) reside on the same or on adjacent atoms. This allows essentially no freedom of variation in the internuclear vectors upon deformation of the network. The primary informational content therefore relates to independent segmental orientation distributions. By placing single spins on alternate segments, there should be much greater sensitivity to changes in the chain extension upon bulk deformation. 

Sulfur tetrafluoride provides an inexpensive method for selectively converting a carbonyl to a difluoromethyl group. However, the reactions involving sulfur tetrafluoride, in general, require pressure equipment constructed of fluorine-resistant material such as Hastelloy-C bombs.8 Phenylsulfur trifluoride may be used to advantage for the same reaction, where small amounts are involved, since the reaction may be run at atmospheric pressure in glass, polyethylene, or metal containers. 

Functional perfluoropolyethers11 (Figure 14.7) can also be prepared by direct fluorination in high yields. Difunctional perfluoropolyethers based on fluorinated polyethylene glycol) are of particular interest as possible precursors for elastomers, which should have outstanding high-temperature and low-temperature properties. 

The best known aspect, and the first one to find commercialization in the direct fluorination area, was the fluorination of polymer surfaces. This Lagow-Margrave invention, trademarked Fluorokote, involved many types of polymeric materials in various forms e.g., polyethylene bottles, polypropylene objects, and rubber gloves. Polyethylene bottles are easily given fluorocarbon surfaces (>0.1 mm), and this has been commercialized. Air Products has at least 20 licenses for what is known as their Aeropak process and Union Carbide has a Linde Fluorination process as well. Applications in chemical, pharmaceutical, and cosmetic storage are widespread. 

Direct fluorination of polymer or polymer membrane surfaces creates a thin layer of partially fluorinated material on the polymer surface. This procedure dramatically changes the permeation rate of gas molecules through polymers. Several publications in collaboration with Professor D. R. Paul62-66 have investigated the gas permeabilities of surface fluorination of low-density polyethylene, polysulfone, poly(4-methyl-1 -pentene), and poly(phenylene oxide) membranes. 

Surface fluorination changes the polymer surface drastically, the most commercially significant use of polymer surface direct fluorination is the creation of barriers against hydrocarbon permeation. The effectiveness of such barriers is enormous, with reductions in permeation rates of two orders of magnitude. Applications that exploit the enhanced barrier properties of surface-fluorinated polymers include (1) Polymer containers, e.g., gas tanks in cars and trucks, which are produced mostly from high-density polyethylene, where surface fluorination is used to decrease the permeation of fuel to the atmosphere and perfume bottles. (2) Polymeric membranes, to improve selectivity commercial production of surface-fluorinated membranes has already started.13... 

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