Polymer-forming gas

The structure dependency of the etching rate is enhanced in chemically reactive luminous gas, but the nature of dependence remains the same. Plasma-sensitive structures such as -O- in the backbone of a polymer- and oxygen-containing pendant group play a dominant role. It is important to note that LCVT, chemical etching of polymers by non-polymer-forming gas plasma, can be well described by the same discharge power parameter for LCVD, which is WjFM. 

The internal stress of plasma polymers is dependent not only on the chemical nature of monomer but also on the conditions of plasma polymerization. In the plasma polymerizations of acetylene and acrylonitrile, apparent correlations are found between and the rate at which the plasma polymer is deposited on the substrate [2], as depicted in Figure 11.3. The effect of copolymerization of N2 and water with acetylene on the internal stress is shown in Figures 11.4 and 11.5. The copolymerization with a non-polymer-forming gas decreases the deposition rate. These figures merely indicate that the internal stress in plasma polymers prepared by radio frequency discharge varies with many factors. The apparent correlation to the parameter plotted could be misleading because these parameters do not necessarily represent the key operational parameter. 

Without addition of the second gas or vapor, i.e., jet of excited argon neutrals With addition of the second gas that does not form the deposition of material (non-polymer-forming gas), i.e., jet of excited neutral species of the second gas, and... 

The creation of chemically reactive species from polymer-forming gas (monomer) in plasma jet of LPCAT follows the same principle described for non-polymer-forming gases, but the major reaction is molecular dissociation of monomer by energy transfer mechanism. Upon addition of monomers to the argon luminous gas jet, the emissions of argon luminous gas are highly quenched. The dominant features... 

The creation of chemically reactive species from polymer-forming gas (monomer) follows the same... 

Since doping affects the etch rate of polysilicon, we investigated the etch rate characteristics of each gas used in the etch process (Table 1). We discovered that, the polysilicon etch rate with SF6 was independent of doping effects. To minimize the isotropic etch characteristics of SF6 in the B.T step(3), we used HBr, which is a well known polymer forming gas, with a SF6 HBr ratio of 1 0.75. With this new process, vertical profiles were obtained after the B.T step, in both types of polysilicon. At the end of the B.T step, the remaining polysilicon thickness in the n-type was comparable to the p-type and was less than the amount of polysilicon after the B.T step In the conventional process (Fig. 2-a 2-b). Also, the later the EP in the M.E step, the thinner was the remaining polysilicon in the p-type, thus... 

Polypropylene. One of the most important appHcations of propylene is as a monomer for the production of polypropylene. Propylene is polymerized by Ziegler-Natta coordination catalysts (92,93). Polymerization is carried out either in the Hquid phase where the polymer forms a slurry of particles, or in the gas phase where the polymer forms dry soHd particles. Propylene polymerization is an exothermic reaction (94). 

Direct Oxidation of Propylene to Propylene Oxide. Comparison of ethylene (qv) and propylene gas-phase oxidation on supported silver and silver—gold catalysts shows propylene oxide formation to be 17 times slower than ethylene oxide (qv) formation and the CO2 formation in the propylene system to be six times faster, accounting for the lower selectivity to propylene oxide than for ethylene oxide. Increasing gold content in the catalyst results in increasing acrolein selectivity (198). In propylene oxidation a polymer forms on the catalyst surface that is oxidized to CO2 (199—201). Studies of propylene oxide oxidation to CO2 on a silver catalyst showed a rate oscillation, presumably owing to polymerization on the catalyst surface upon subsequent oxidation (202). 

Since this initial report, there is only one other report for M-NHC catalysed copolymerisation of CO/alkenes [52]. Lin and co-workers synthesised the fcw-NHC complex dication 41, that copolymerises CO and norbomene. The copolymer is synthesised in 87% yield by employing 0.5 mol% 41, and 750 psi CO gas after 3 days at 60°C. The polymer formed contains 37 repeat units and = 4660 and M = 3790. 

Gaseous monomers can polymerize in the gas phase in the presence of a fluidized catalyst bed. As polymer forms, hot gas forces the newly made material out of the reactor to a collector. Figure 2.15 shows a simplified schematic diagram of a generic polymerization reactor. 

Most of the more recent studies have concentrated on rhodium. An effective system for a gas-phase reaction was reported by Arai et al. (107). The catalyst support was silica gel, which was desirable for its high surface area properties (293 m3/g). This was covered with a polymer formed from styrene and divinylbenzene, either by emulsion (A) or by solution (B) polymerization. Each of these base materials was then functionalized by the reactions shown in Eq. (49). 

Foams are commercially produced several ways. Some polymerization processes produce their own foam. Polyurethanes, for example, are very exothermic. When they are formed, if a little water is present, CO2 will be a by-product. As the polymer forms, the CO2 will cause closed cell foam. As another example, a blowing agent can be injected into the molten polymer. The agent will later decompose, giving off a gas when the polymer is heated to melting. Epoxy resins are expanded into foams this way. 

Crystalline particles that produce gaseous oxidizer fragments are used as oxidizer components and hydrocarbon polymers that produce gaseous fuel fragments are used as fuel components. Mixtures of these crystalline particles and hydrocarbon polymers form energetic materials that are termed composite propellants . The oxidizer and fuel components produced at the burning surface of each component mix together to form a stoichiometrically balanced reactive gas in the gas phase. 

Another characteristic is that most involve multiple phases, the explicit subject of the next chapter. The polymer formed is a Hquid or solid, while the monomer is a gas or Hquid. In condensation polymerization water is frequently a byproduct so in many polymerization processes there will be an aqueous phase as well as an organic phase. 

Table 4.1 Three glassy polymers used to form gas-separation membranes.

The technologies that have been developed for the production of polyolefins, olefin homopolymers and copolymers are slurry, solution and gas-phase polymerisation bulk polymerisation of propylene in the liquid monomer as a special case of the slurry process has also emerged. The fundamental differences in the various olefin polymerisation processes reflect the different approaches that have been devised to remove the substantial heat of polymerisation. In addition, processes can be operated in a batch or a continuous mode. In the batch process the reagents are loaded into a polymerisation vessel, the polymer forms and the vessel is emptied before a new charge of reagents is introduced. In the continuous process, the catalyst precursor, activator and other necessary... 

This conversion, similar to that of butenes to butadiene (see Section 6.1.1.1), is carried out by Shell in the presence of steam, on an Fe203/Cr203/K2C03 catalyst, at about 600"C The effluent is cooled by oil which absorbs the polymers formed The gas is then compressed before separation, which comprises extractive distillation with aqueous aceto> nitrile, followed by rectification of the isoprene. Shell daims the ability to treat butenes and isoamylenes simultaneously to produce butadiene and isoprene. Some idea of the composition of the effluents from sulfuric add extraction and dehydrogenation is given by Table 6.6. 

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