Peroxides accelerators

Applications As the basic process of electron transfer at an electrode is a fundamental electrochemical principle, polarography can widely be applied. Polarography can be used to determine electroreductible substances such as monomers, organic peroxides, accelerators and antioxidants in solvent extracts of polymers. Residual amounts of monomers remain in manufactured batches of (co)polymers. For food-packaging applications, it is necessary to ensure that the content of such monomers is below regulated level. Polarography has been used for a variety of monomers (styrene, a-methylstyrene, acrylic acid, acrylamide, acrylonitrile, methylmethacrylate) in... 

The effect of jumping of the maximal hydroperoxide concentration after the introduction of hydrogen peroxide is caused by the following processes. The cumyl hydroperoxide formed during the cumene oxidation is hydrolyzed slowly to produce phenol. The concentration of phenol increases in time and phenol retards the oxidation. The concentration of hydroperoxide achieves its maximum when the rate of cumene oxidation inhibited by phenol becomes equal to the rate of hydroperoxide decomposition. The lower the rate of oxidation the higher the phenol concentration. Hydrogen peroxide efficiently oxidizes phenol, which was shown in special experiments [8]. Therefore, the introduction of hydrogen peroxide accelerates cumene oxidation and increases the yield of hydroperoxide. 

The alkylations of the oxazolidinone-containing amide enolate of Figure 13.43 occur with diastereoselectivities of 93 7 and > 99 1, respectively. The hydrogen peroxide-accelerated alkaline hydrolysis of these compounds occurs with complete retention of the previously established configuration at the a-stereocenter. To date, the Evans synthesis offers the most versatile access to enantiomerically pure a-alkylated carboxylic acids. 

The various curing agents used for manufacturing rubber lining compounds are sulfur, organic peroxides, accelerators with available sulfur and metallic oxides. 

The catalyst can be activated for hydrogenation by small quantities of oxygen or by addition of hydrogen peroxide. Acceleration by factors varying from 1.5 to 4 can be realized. Presumably one triphenylphosphine ligand is displaced as triphenylphosphine oxide.3... 

Within the different types of epoxies, are found epoxy diacrylates or vinyl ester resins, used to produce specific corrosion and chemical resistant composite systems. Vinyl ester resins are produced by either reacting epoxy resins of glycidyl derivatives with methacrylic acid, or from BPA and glycidyl methacrylates, where an active monomer (usually styrene) as crosslinker, hardener (usually organic peroxides), accelerators (cobalt) are added to the system. In the thermoset epoxy systems, there are also the mould releasers , which can be either internal such as, lecithin, or stearates of zinc and calcium, certain organic phosphates that are mixed in the resin, or, external - such as, fluorocarbons, silicone oil, and certain waxes, that are directly laid on the mould. 

The effect of peroxide accelerators [32] can be supported by so-called promoters (activators), which do not act as accelerators when used alone. 

N-Cyclohexyl-2-benzothiazolesulfenamide 1,3-Dibutylthiourea Dicyclohexylbenzothiazyl-2-sulfenamide Dimethyl diphenyl thiuram disulfide 2,6-Dimethylmorpholine Diphenylamine 4,4 -Dithiodimorpholine 2-Ethylbutyraldehyde Ethyl morpholine Formaldehyde aniline 2,6-Lutidine N-Nitrosodimethylamine Paraldehyde p-Quinone dioxime Selenium Selenium dimethyidithiocarbamate Sodium diethyidithiocarbamate Sodium dimethyidithiocarbamate Sodium nitrite N,N,N, N -Tetrabenzylthiuram disulfide Tetraisobutylthiuram disulfide Tetramethylthiuram disulfide Thiocarbamyl sulfenamide Thiophenol Thiourea Triethanolamine Triethylamine Triethylenetetramine n-Valeraldehyde Zinc dialkyl dithiophosphate Zinc diamyidithiocarbamate Zinc dibenzyl dithiocarbamate Zinc diisobutyidithiocarbamate Zinc isopropyl xanthate Zinc 2-mercaptobenzothiazole Zinc oxide Zinc-N-pentamethylene dithiocarbamate Zinc peroxide accelerator, rubber articles for repeated use food-contact... 

The term refers to any chemical substance added to a plastic or elastomer compound to impart or improve certain end-use properties. Common additives are foam agents, colorants, curatives like sulfur or peroxide, accelerators, activators, tackiness agent, stabilizer packages, carbon black, clay. Refer to Carbon Black, Antizonanty and Antioxidants. 

In the case of PS, the weak sites of the polymer chain are the tertiary carhon atoms attached to the phenyl groups, which are vulnerable to attack by free radicals. At these weak sites, a series of chemical reactions can lead to cleavage of the chain and initiate the formation of carbonyl groups [21, 22] the presence of carbonyl groups, as well as moieties capable of forming free radicals, such as peroxides, accelerates degradation [18, 23]. 

A typical composition for BMC and SMC includes base resins, catalysts, peroxides accelerators, fillers/chopped GF, thickeners and other additives. The base resins that are usually used are either polyester-based (orthophthalic or isophthalic), which are used with styrene, acrylic, vinyl toluene or di-allyl-phthalate (DAP) monomers, as crosslinkers, or styrene type monomers for general purpose products. Acrylic base resins are used for low shrinkage, while vinyl type monomers for high hot strengths (heat deflection temperatures). Catalysts are used for polyester type resins. Peroxides, such as benzoyl peroxide (BPO) and butyl perbenzoate are used as high temperature catalysts. 

Examples of some important initiators are ethyl methyl ketone peroxide, cyclohexanone peroxide, benzoyl peroxide and cumene peroxide. Accelerator is a reducing agent, such as cobalt octoate, which is added in very small quantity to catalyze decomposition of the initiator into free radicals. Aromatic amines such as dimethyl aniline or dimethyl /j-toluidine are added to promote that reaction. The two components are combined prior to application, ensuring even distribution of initiator in the system. The dosage of initiator, accelerator, promoter and inhibitor will determine the pot life, the longest period of time during which mixture is still usable and can be applied. 

Plate V(Chapter 7) Appearance of silicate sealed, peroxide accelerated cerium-based conversion coating, without exposure to NSS and after 168 and 336 hours NSS. 

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