Polymerization granular resins

The discovery of PTFE (1) in 1938 opened the commercial field of perfluoropolymers. Initial production of PTFE was directed toward the World War II effort, and commercial production was delayed by Du Pont until 1947. Commercial PTFE is manufactured by two different polymerization techniques that result in two different types of chemically identical polymer. Suspension polymerization produces a granular resin, and emulsion polymerization produces the coagulated dispersion that is often referred to as a fine powder or PTFE dispersion. 

Suspension polymerization either little or no dispersion agent is used and vigorous agitation is maintained. A precipitated resin, commonly referred to as granular resin, is produced. 

Pure tetrafluoroethylene monomer under ambient conditions is an odorless, colorless, tasteless gas with low toxicity. It may be polymerized by either suspension or emulsion techniques. Both procedures require use of high pressures in an autoclave in order to maintain the monomer in liquid form. These techniques produce chemically identical product, the first a granular resin, and the second a fine powder (Eq. 23.7). 

PTFE is produced by free-radical polymerization mechanism in an aqueous media via addition polymerization of tetrafluoroethylene in a batch process. The initiator for the polymerization is usually a water-soluble peroxide, such as ammonium persulfate or disuccinic peroxide. A redox catalyst is used for low temperature polymerization. PTFE is produced by suspension (or slurry) polymerization without a surfactant to obtain granular resins or with a perfluori-nated surfactant emulsion polymerization) to produce fine powder and dispersion products. Polymerization temperature and pressure usually range from 0 to 100°C and 0.7 to 3.5 MPa. 

The granular resin is conveyed from the polymerization system to a bin for purging with nitrogen to remove residual hydrocarbons and then to pelleting. 

Granular Resins. Granular PTFE is made by polymerizing TFE alone or in the presence of trace amoimts of comonomers (42-44). An initiator, a small amount of dispersing agent, and other additives (45) may be present an alkaline... 

Method of synthesis granular resin, water dispersions, and powdered resins are produced by free radical polymerization in aqueous medium TFE polymerizes linearly without branching micropowders are produced by irradiation of PTFE by high energy electron beam or polymerization controlled to produce lower molecular weight Diobny, J G, Fluoroplastics, Rapra, 2006. 

The dark-colored clarified liquor is presure-filtered and concentrated to 60 percent solids in multiple-effect evaporators. The concentrated liquor is decolorized with granular carbon in columns 12 ft in diameter and 30 ft high in a countercurrent manner that is, liquor flows upward in the columns, while a portion of the carbon is removed from the bottom periodically. Carbon is used at a rate of 2.5 percent of dry solid processed, and approximately 5 percent of carbon is lost during revivification.91 In some cases, granular carbon has been replaced by synthetic polymeric adsorbents to decolorize the syrup. Low ash syrups usually are deionized with ion-exchange resins. The processed liquor is evaporated to a final solids content of 75-85 percent in a single-effect evaporator. 

Granular anion-exchange resins have been prepared from N-containing C-vinyl heterocyclics, polyvinyl compounds and one or more aliphatic vinyl compounds in an aqueous phase in presence of water-insoluble suspension stabilizers Thus, a mixture of 4-vinylpyridine, ethylacrylate, and p-DVB on polymerization using hydroxylapatite as suspension stabilizer and AIBN as the initiator gives an anion-exchange resin. 

Granular PTFE resins are produced by polymerizing tetrafluoroethylene alone or with a trace of comonomers [19,20] with initiator and sometimes in the presence of an alkaline buffer in aqueous suspension medium. The product from the autoclave can consist of a mixture of water with particles of polymer of variable size and irregular shape. After the water is removed from the mixture, the polymer is dried. 

The vast majority of modern resins are produced by the addition polymerization route and take the form of spherical beads. A few condensation polymer products remain available and these have an amorphous granular appearance. 

Commercially, PTFE is produced from the monomer tetrafluoroethylene by two different polymerization techniques, namely, suspension and emulsion polymerization. These processes give two vastly different physical forms of chemically identical PTFE. While suspension polymerization produces granular PTFE resin, emulsion polymerization produces an aqueous PTFE dispersion and PTFE fine powders (after coagulating the dispersion). 

Besides the conventional granular or bead form, ion-exchange resins are now marketed in the form of membranes, usually 1 to 2 mm thick. Homogeneous membranes have been prepared by partial polymerization of the resin to a syrup, which is then poured into a mould and finally polymerized in situ. Since these are mechanically weak, it is more usual to construct membranes from beads which are held together with a binding agent of polythene, polyvinyl chloride or polymethyl methacrylate. These may contain up to 75 per cent of resin.i... 

The molding resins compounded with fillers and reinforcement are marketed usually in granular or pellet form. They are partly polymerized for final molding under heat and pressure. The molding step completes the polymerization, making the product infusible and relatively insoluble. Phenolic resins may also come as resinous solutions. 

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