Radical polymerization inhibitors

The generation of free radicals usually does not immediately start polymerization in commercial adhesives. These contain small amounts of inhibitors, which are chemical compounds that prevent free radical polymerization. Inhibitors are purposely added to acrylic adhesives to obtain practical shelf life. Inhibitors stop polymerization by reacting with active free radicals to form a less reactive species... 

Because they are acrylic monomers, alkyl cyanoacrylate esters still require the addition of radical polymerization inhibitors, such as hydroquinone or hindered phenols, to prevent radically induced polymerization over time [3j. Since basic initiation of alkyl cyanoacrylate monomers is the predominant polymerization mechanism, large quantities of free radical inhibitors can be added, with little or no effect on adhesive performance. 

Title A -Alkoxy-4,4-Dioxy-Polyalkyl-Piperidines as Radical Polymerization Inhibitors... 

Free radical polymerization inhibitors have been prepared by reacting tetramethylpi-peridive oxyl derivatives with selected glycidyl intermediates. When used as a styrene polymerization regulator in 1.0mol% and 0.1mol% at 120°C, molecular weights of 2400 and 43,400 daltons, respectively, were obtained. 

In the two-step process, the second-stage reactor is similar to the first-stage reactor but is packed with an optimized catalyst for aldehyde oxidation, based on Mo V oxides, and is run under different operating conditions. Care must be exercised during the separation and purification phases to avoid conditions favouring acrylic acid polymerization, e.g., by addition of a radical polymerization inhibitor such as the hydroquinone monomethyl ether. Selectivities to acrylic acid are higher than 90% at total conversion of the aldehyde. Overall yields referred to propylene are in the range 75-85%. Most acrylic acid produced is esterified for the production of acrylate esters. 

The decomposition inhibitors are free radical polymerization inhibitors. 

Materials. VTMSK (III) was synthesized in a four-step reaction sequence, as reported previously (ii). The bright-yellow monomer was stored in a sealed glass ampoule over a free-radical-polymerization inhibitor at -15 °C. IPTMSK (IV) was obtained by a procedure reported by Danheiser et al. (13) and stored as just described. All the spectroscopic properties of VTMSK and IPTMSK were in agreement with the literature data (12, 13). 

The products 3a-3d are obtained as colorless, moisture-sensitive liquids. A radical polymerization inhibitor (e.g., HQME) is added and the products are stored under light exclusion in order to prevent undesired polymerization. 

The formation of alternating copolymers through the polymerization of pairs of monomers, one of which is the donor and the other the acceptor of an electron, is well known. We shall mention only a few studies out of a great number of those recently published. First, those dealing with the nature of active centers in such systems will be examined. When radical initiators are used, e.g., benzoyl peroxide as in17), and the reaction is inhibited with different radical polymerization inhibitors, such as stable radicals like 2,2,6,6-tetramethylpiperidine 1-oxide, quinones, fluorene etc., questions concerning the nature of active centers can be regarded as solved. 

THE USE OF PHENOLIC COMPOUNDS AS FREE-RADICAL POLYMERIZATION INHIBITORS... 

Radical polymerization inhibitors are therefore molecules that are able of reacting with the radicals present in the monomer (either alkyl radicals or peroxy radicals) to give very low reactive radicals which will stop the chain growth. It should be noted that the formation of these products (inert in terms of the polyaddition reaction) can result from several basic and consecutive reactions. This is why inhibition mechanism can sometimes be rather complex. 

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). 

Q-1300,-1301. [WakoChem.USA] N-Nitrosophenylhydroxylamine salts analytical reagents, radical polymerization inhibitor, chelating agent, antioxidant, r ric. chemicals, germicides, fungicides. 

MAJOR USES Insecticide herbicide fungicide free radical polymerization inhibitor used in emulsifiable concentrate formulations used in the dyestuff industry. 

OTHER COMMENTS used in industry as a selective herbicide and insecticide used in the dyestuff industry used as a free-radical polymerization inhibitor. 

This problem has been solved by careful choice of anionic polymerization inhibitors. The materials employed are acidic compounds present at levels between 5 and 100 ppm. Table 1 shows a list of typical additives. Free radical polymerization inhibitors are also added. These are phenolic compounds such as hydroquinone or hindered phenols. 

The two types of inhibitors used in cyanoacrylate adhesives are radical polymerization inhibitors and anionic polymerization inhibitors. The former type are usually phenolic, for example, hydroquinone, p-methyloxyphenol, or hindered phenolics. They are generally employed in 0.1-1.0% concentrations. The amine- or sulfur-based inhibitors and the metal-chelating inhibitors should be avoided owing to their nucleophilic character. Radical inhibitors are used to protect the adhesive during storage from polymerization induced by heat or light and other adventitious radical sources. These... 

It should not interfere with the photoreaction, e.g. as a triplet-state quencher of a photoinitiator or photosensitizer, or as a free-radical polymerization inhibitor. 

Free radical polymerization inhibitors such as hydroquinone usually are added to the resin mixture to prolong storage life. The presence of these inhibitors causes an induction period in the final curing step. The system will gel after about 1 percent cross-linking takes place, and then the rate of curing rapidly... 

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