Polymerization inhibitors hydroquinone

FIGURE 5.13 Left low MWCO membrane (deionized water 2-methoxyethanol = 3.7 1). Right high MWCO membrane (deionized water 2-methoxyethanol = 0.34 1). The post diameter is 50 pm. For phase-separation polymerization, the monomer is 2-(N-3-sulfo-propyl-N,N-dimethylammonium) ethyl methacrylate, the cross-tinker is methylene bisacry-lamide, and the plotoinitiator is 2,2 -azobis(2-methylpropanimidamide dihydrochloride). To prevent unwanted polymerization that may occur by heat and molecular diffusion outside the UV-irradiated region, a polymerization inhibitor, hydroquinone, is also added. To facilitate covalent attachment of the porous membrane to the silica surface, it is first coated with 3-(trimethoxysilyl)propylacrylate [347]. Reprinted with permission from the American Chemical Society. 

Hydroquinone s. under Polymerization inhibitors Hydroquinones s. Quinols Hydrosilylation 26, 642... 

The polymeric products can be made to vary widely in physical properties through controlled variation in the ratios of monomers employed in thek preparation, cross-linking, and control of molecular weight. They share common quaHties of high resistance to chemical and environmental attack, excellent clarity, and attractive strength properties (see Acrylic ester polymers). In addition to acryHc acid itself, methyl, ethyl, butyl, isobutyl, and 2-ethylhexyl acrylates are manufactured on a large scale and are available in better than 98—99% purity (4). They usually contain 10—200 ppm of hydroquinone monomethyl ether as polymerization inhibitor. 

Sulfuric acid is also a very satisfactory catalyst aluminum alkoxides also are useful, especially when the alcohols would be adversely affected by strong acids. Sodium alkoxides produce undesirable side reactions and give lower yields. When alkaline catalysts are employed, an alkaline polymerization inhibitor, such as j j-phenylenediamine or phenyl-d-naphthylamine, should be used instead of hydroquinone. 

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]. 

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. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reaction Stability During Transport Stable when inhibited Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Undergoes uncatalyzed polymerization reaction around 200°C. Light promotes polymerization Inhibitor of Polymerization Hydroquinone 0.10 to 0.25 %. 

Methylparathion is the corresponding dimethyl derivative. Later (1952) malathion found favour because of its decreased toxicity to mammals it is readily made in 90% yield by the addition of dimethyidithiophosphate to diethylmaleate in the presence of NEtr as a cataly.st and hydroquinone as a polymerization inhibitor ... 

Methyl Methacrylate CH2=C(CH3)COOCH3 Impure Methyl-Methacrylate Vap in Air 2.1 to 12.5% > Ambient > 110 Inhibitor-Hydroquinone or Methyl Ether of Hydro-quinone. Shield from light avoid sparks. Store in cool place 13.3-13.8 421 Self-polymerizing initiated by visible light at 20 to 40°... 

The Diels-Alder cycloaddition of furan and acrylic acid, in the presence of hydroquinone as a polymerization inhibitor, provided enrfo-7-oxabicy-clo[2.2.1]hept-5-ene-2-carboxylic acid - (29) in a yield of 45%. Compound 29 was found to be the most accessible and important starting-material for the synthesis of various racemic carba-sugars, as well as their enantiomers. 

Benzoquinone was first produced commercially in 1919, and has since been manufactured in several European countries, Japan and the United States. Its major use is in hydroquinone production, but it is also used as a polymerization inhibitor and as an intermediate in the production of a variety of substances, including rubber accelerators and oxidizing agents (lARC, 1977). 

Bicyclic bridged phosphorinane derivatives can be synthesized by different methods. When phenylphosphine is heated with cycloocta-2,7-dienone to 135 °C in the presence of polymerization inhibitors, e.g. hydroquinone, and the double Michael addition product is oxidized, the two crystalline syn and anti isomers (total yield 48-59%) are isolated. Separation by crystallization gives the pure compounds which can in turn be transformed at the carbonyl or the phosphorus group (equation 10) (75T33,76JOC589). 

The synthesis, which at room temperature may require days, or even weeks, needs an alkylated phenol, hydroquinone, copper stearate or other polymerization inhibitor, but often the use of elevated temperatures and appropriate solvents (aliphatic hydrocarbons, CH2C12) allows a more rapid cycloaddition. 

Polymerization inhibitors stop or slow down polymerization by reacting with the initiator or growing-chain radicals. A wide variety of substances can behave as inhibitors quinones, hydroquinones, aromatic nitro compounds, aromatic amines, and so on. In cases where the inhibitor is a hydrogen donor (symbolized here by InH), then for inhibition to occur, the radical resulting from hydrogen transfer (In-) must be too stable to add to monomer. If it does add to monomer and starts a new chain, chain transfer occurs instead of inhibition. For perfect inhibition, the In- radicals must combine with themselves (or initiator radicals) to give inert products ... 

Vinyl chloride is generally transported via pipeline, and in railroad tank cars and tanker ships. Containers of vinyl chloride must be labeled "vinyl chloride," "extremely flammable gas under pressure," and "cancer-suspect agent" (146). Because hazardous peroxides can form on standing in air, especially in the presence of iron impurities, vinyl chloride should be handled and transported under an inert atmosphere. The presence of peroxide from vinyl chloride and air can initiate polymerization of stored vinyl chloride however, stabilizer can be added to prevent polymerization. Inhibitors such as hydroquinone [123-31-9] are often added, particularly when shipping long distances in warmer climates. 

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. 

Eastman Kodak Co. hydroquinone, m.p. 172-174°, was used. 4-f-Butylpyrocatechol, m.p. 38-42°, from the same supplier, proved to be an equally effective polymerization inhibitor. 

Methyl Acrylate CH2=CHC00CH3 Non-inhibitors such as Biphenyl, Bibenzyl, Tri-phenyl, etc Methyl Acrylate Vap plus air > Ambient > 120 Inhibitor—Hydroquinone or Methyl Ether of Hydro-quinone 10-20ppm. Store Store below 10° no inert atmosphere. No sparks 18.58-18.8 463 Self polymerizing above ambient press temp accelerates polymerization... 

Hydroquinone or another polymerization inhibitor should be added before distillation of acrylic acid or its esters. 

Photographic reducer and developer reagent for the determination of small quantities of phosphate, dye intermediate stabilizer in paints and varnishes motor fuels and oils antioxidant for fats and oils, and a polymerization inhibitor. Therapeutically used topically for depigmentation to treat skin blemishes, for example, hypermelanosis. Hydroquinone occurs naturally, as a conjugate with jS-o-glucopyranoside, in the leaves, bark, and fruit of a number of plants, and its presence may be an important factor in fire-blight resistance in the pear. It may also play an important part in the defense mechanisms of some insects. 

Polymerization inhibitor r-Butylcatechol and triethylamine (see 1,1-Dichloroethyleiie). Hydroquinone (see Formic acid). Phenyl- 8-naphthylamine. 

Acidolysis. One method for the preparation of anhydrous acrylic acid is by heating methyl acrylate with 98% formic acid in the presence of a catalytic amount of sulfuric acid and of hydroquinone as polymerization inhibitor. ... 

Transesterificalion. In the conversion of methyl acrylate to n-butyl acrylate, hydroquinone was added as polymerization inhibitor. The mixture was heated at... 

Properties Colorless or yellowish liquid disagreeable, choking odor.Bp 52.7C, mp -87.0C, d 0.8427 (20/20C), bulk d 7.03 lb/gal (20C). Flash p below OF (-17C) (COC), autoign temp 532F (277C). Soluble in water, alcohol, and ether. Polymerizes readily unless inhibitor (hydroquinone) is added. Very reactive. 

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