Monomer polymerized into powder

Chemically, THV Fluoroplastic (hereafter referred to as THV) is a terpolymer of tetrafluoroethylene (TFE), hexafluoropropylene (HFP), and vinylidene fluoride (VDF) produced by emulsion polymerization. The resulting dispersion is either processed into powders and pellets or concentrated with emulsifier and supplied in that form to the market.91 Currently, the manufacturer is Dyneon LLC and there are essentially nine commercial grades (five dry and four aqueous dispersions) available that differ in the monomer ratios and consequently in melting points, chemical resistance, and flexibility. 

Ethylene, hydrogen, co-monomer and a super-high activity catalyst are fed into the reactors (1). Polymerization reaction occurs under a slurry state. The automatic polymer property control system plays a very effective role in product-quality control. Slurry from the reactors is pumped to the separation system (2). The wetcake is dried into powder in the dryer system (3). As much as 90% of the solvent is separated from the slurry and is directly recycled to the reactors without any treatment. The dry powder is pelletized in the pelletizing system (4) along with required stabilizers. 

In 1972, Liepins and Sakaoku [7] reported that polymeric powders were formed nearly exclusively in the radio frequency reactors shown in Figures 8.12 and 8.13, in which an organic vapor was introduced into the glow discharge of a carrier gas. The monomers that formed powders nearly exclusively and the yield of powder formation are summarized in Table 8.1. Monomers that did not form powders exclusively (i.e., formed plasma polymer in the form of a film or a film with powders) are shown in Table 8.2. The significant points about these experiments are as follows ... 

For clinical applications in dentistry, it is convenient to work with mixtures made from a polymeric powder and a liquid monomer. The mixture attains a doughy consistency, and it can then be formed into intricate shapes. Subsequently, as a result of the combination of reactants in the powder and liquid, the monomer polymerizes to provide a rigid load-bearing material. This is usually a two-phase material in which the dispersed phase is attributable to particles originally present in the powder. Many proprietary materials comprise two phases of poly (methyl methacrylate), although other ingredients may be included to modify appearance and properties. 

Acrylics. Acetone is converted via the intermediate acetone cyanohydrin to the monomer methyl methacrylate (MMA) [80-62-6]. The MMA is polymerized to poly(methyl methacrylate) (PMMA) to make the familiar clear acryUc sheet. PMMA is also used in mol ding and extmsion powders. Hydrolysis of acetone cyanohydrin gives methacrylic acid (MAA), a monomer which goes direcdy into acryUc latexes, carboxylated styrene—butadiene polymers, or ethylene—MAA ionomers. As part of the methacrylic stmcture, acetone is found in the following major end use products acryUc sheet mol ding resins, impact modifiers and processing aids, acryUc film, ABS and polyester resin modifiers, surface coatings, acryUc lacquers, emulsion polymers, petroleum chemicals, and various copolymers (see METHACRYLIC ACID AND DERIVATIVES METHACRYLIC POLYMERS). 

The addition—reaction product of bisphenol A [80-05-07] and glycidyl methacrylate [106-91-2] is a compromise between epoxy and methacrylate resins (245). This BSI—GMA resin polymerizes through a free-radical induced covalent bonding of methacrylate rather than the epoxide reaction of epoxy resins (246). Mineral fillers coated with a silane coupling agent, which bond the powdered inorganic fillers chemically to the resin matrix, are incorporated into BSI—GMA monomer diluted with other methacrylate monomers to make it less viscous (245). A second monomer commonly used to make composites is urethane dimethacrylate [69766-88-7]. 

For NMR spectroscopic experiments, a thin film of pTrMPTrA was prepared by reacting a quantity of monomer and photoinitiator confined between glass plates with 1 mm separation. The polymerization conditions were the same as those for the photocalorimetry experiments. After 1 hour of UV exposure, the film was removed from the plates and ground to a fine powder using a mortar and pestle. A solid-state 13C NMR spectrum of the powder was obtained immediately, as described below. The remaining polymer powder was divided into two portions, one of which was stored under atmospheric conditions. The other portion was stored under N2. After one week, 13c spectra were again obtained for each of these polymer samples. Both samples were then heated to 280 °C in a vacuum oven and analyzed once more by 13C NMR spectroscopy. 

Charge Exchange on the Surface of Discharge Electrode. In general, the polymerization process in plasma may be divided into three processes, i. e. the ionization of monomer, the transportation of active particles and polymerization. In a certain discharge condition, the polymerization was supposed to occur in gas phase and powder like polymers were obtained. In our experimental condition, no powder was obtained. Therefore, the polymerization must be initiated on the substrate. 

One of the most successful petrochemical applications is illustrated in Figure 8.14 treatment of resin-degassing vent gas in a polyolefin plant [28]. In these plants, olefin monomer, catalyst, solvents, and other coreactants are fed at high pressure into a polymerization reactor. The polymer product (resin) is removed from the reactor and separated from excess monomer in a flash-separation step. The recovered monomer is recycled to the reactor. Residual monomer is removed from the resin powder by... 

Diacrylate monomers have been prepared that are photocurable in visible light and that have small polymerization shrinkage and high X-ray contrast properties. When polymerized with 0.01 to 0.04 pm glass powder, these dental composites were easily machined into artificial teeth. 

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