Polymerization inhibitors oxygen

Addition of the initiator followed by purging of the mixture with nitrogen in order to remove the polymerization inhibitor oxygen. 

Polymerization inhibitors are key additives which prevent premature gelation of the adhesive. The foimulator must carefully balance shelf stability and the required cure on demand. Due to its high propagation rate, MMA is difficult to inhibit. Some comments on specific inhibitors follow. The most common inhibitor to be found in component monomers is 4-methoxyphenol, which is also called the methyl ether of hydroquinone. This inhibitor is effective only in the presence of oxygen. A mechanism has been proposed, and is illustrated in Scheme 13 [128]. 

The use of vinyl monomers for gel formation requires a polymerization process in the formation. This technique is used to enable a solution to gel slowly even at high temperatures. An aqueous solution of a vinyl monomer is mixed with a radical-forming initiator, and if necessary, with a dispersant. The initiator decomposes at elevated temperatures and initiates the polymerization process. In this way, a gel is formed in place. The polymerization process is sensitive to molecular oxygen. To further delay curing, polymerization inhibitors may be added to the solution in small amounts. This technique is used in the treatment of subterranean formations, especially for plugging lost... 

In the paper published in 1900, he reported that hexaphenylethane (2) existed in an equilibrium mixture with 1. In 1968, the structure of the dimer of 1 was corrected to be l-diphenylmethylene-4-triphenylmethyl-2,5-cyclohexadiene 3, not 2 [38]. Since Gomberg s discovery, a number of stable radicals have been synthesized and characterized, e.g., triarylmethyls, phenoxyls, diphenylpicryl-hydrazyl and its analogs, and nitroxides [39-43]. The radical 1 is stable, if oxygen, iodine, and other materials which react easily with it are absent. Such stable radicals scarcely initiate vinyl polymerization, but they easily combine with reactive (short-lived) propagating radicals to form non-paramagnetic compounds. Thus, these stable radicals have been used as radical scavengers or polymerization inhibitors in radical polymerization. 

Vinylidene Chloride Monoperoxide. When vinyli-dene chloride is stored without a polymerization inhibitor (such as tertiary butyl catechol or other phenol type inhibitors) at a temp of between -40 and +25° in the presence of air or oxygen, the 02 dissolves to form a peroxide compd of undetermined nature which is an extremely violent expl This peroxide seems to act as a polymerization catalyst because its formation is often accompanied by the pptn of a flocculent vinylidene chloride polymer. Since the peroxide is absorbed on the pptd polymer, any separation... 

Thus in radical polymerizations, elementary oxygen is always an inhibitor. Its inhibiting effects in the polymerizations of styrene, vinyl acetate, vinyl chloride, the acrylates and methacrylates, were described some years ago [89, 90]. 

Fig. 8 A typical example of the effect of stirring on the progress of the emulsion polymerization of St in the presence of a typical inhibitor oxygen (40 °C, initiator H2O2)...

Use Polymerization inhibitor of olefins up to 200C, Diels-Alder reaction, catalyst, paint drier, oxygen stripping agent. 

During storage, styrene polymerization is prevented by maintaining low temperature and using an appropriate polymerization inhibitor. The industry standard styrene storage inhibitor is TBC and is typically used at concentrations between 10 ppm and 15 ppm. To be effective, TBC requires dissolved oxygen to be present in concentrations roughly equal to the TBC concentration. 

Polymerization is inhibited by typical free-radical inhibitors oxygen, diphenylpicrylhydrazyl, p-benzoquinone, hydroquinone, p-naphtylamine, etc. 

Reactivity Toward Oxygen, Hydrogen Donors, and Additives This is exemplified by the following results obtained for the reaction between initiating radicals and propagating radicals and well-known radical polymerization inhibitors such as oxygen, HQME (hydroquinone methylether) or TEMPO (2,2,6,6, tetra-methylpiperidine N-oxyl radical). 

Such polymerization can be avoided by using a catalyst composed of a Group VIII metal or a derivative thereof, e.g., platinum (as platinum black or platinized asbestos or charcoal), hydrogen hexachloroplatinate, or ruthenium chloride then the 1 1 adducts can be obtained in good yield from olefins such as styrene, acrylonitrile, and methacrylic esters with, e.g., dichloro(methyl)-silane 347-349 nevertheless it is advantageous to exclude oxygen and add a polymerization inhibitor such as te/7-butylpyrocatechol or 2,6-di-terf-butyl-4-methylphenol. 

Vinyl acetate also may contain dissolved oxygen which acts as a polymerization inhibitor. Table II [20,21] illustrates the actions on the polymerization process of a variety of typical impurities found in vinyl acetate. 

Uses Catalyst for synthesis of pyridines from alkynes and nitriles polymerization inhibitor of olefins up to 200 C in Diels-Alder reactions as paint drier oxygen stripping agent Manuf/Distrib. Acres Org. http //www.acros.be-, Aldrich http //www.sigma-aidrich.com, Alfa Aesar http //www.aifa.com, Boulder Scientific Pfaltz Bauer http //www.pfaltzandbauer.com Strem Chems. http //www.strem.com... 

Uses Reducing agent corrosion inhibitor wastewater treatment electrolytic plating redox reactions polymerization catalyst organic hydrazine derivs. rocket propellant corrosion inhibitor, oxygen scavenger in boiler... 

Recently, also the synthesis of VF2 from 1,1-difluorethane on contact with Cr203/ AI2O3 based catalysts in the presence of oxygen has been reported [527]. Vinylidene fluoride is usually stored and shipped without polymerization inhibitors. If desired, terpenes or quinones can be added to inhibit polymerization. Before use the monomer has to be distilled and degassed several times to remove impurities [528]. Since vinylidene fluoride is a gas under normal conditions, most of the polymerization processes are carried out under pressure. The advantage of poly(vinylidene fluoride) is its good solubility in solvents such as dimethylacetamide (DMA), dimethylformamide (DMF), or dimethyl sulfoxide (DMSO). This fact allows its commercial processing without any problems. Industrially, polymerization is usually accomplished in suspension or emulsion as described in several patents [529-533]. Vinylidene fluoride can also be polymerized with... 

All the acrylate resins suffer a severe risk of homopolymerization. One can even safely state that without correct stabilization these resins cannot be made. The most often applied stabilization package consists of a phenolic stabilizer such as 2,6-di-t-butyl-4-methylphenol in combination with air it is especially the oxygen in air that is required. Oxygen is a very efficient acrylate polymerization inhibitor... 

Some products need at least a small amount of oxygen to be stored safely. This includes styrene and some other vinyl monomers, which must have some oxygen in them to make the usual polymerization inhibitor for styrene (t-butyl catechol, or TBC), effective. If pure nitrogen, for example, is used to blanket styrene, the inhibitor will become ineffective. TBC customarily is added to... 

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