Amine accelerators

The action of redox metal promoters with MEKP appears to be highly specific. Cobalt salts appear to be a unique component of commercial redox systems, although vanadium appears to provide similar activity with MEKP. Cobalt activity can be supplemented by potassium and 2inc naphthenates in systems requiring low cured resin color lithium and lead naphthenates also act in a similar role. Quaternary ammonium salts (14) and tertiary amines accelerate the reaction rate of redox catalyst systems. The tertiary amines form beneficial complexes with the cobalt promoters, faciUtating the transition to the lower oxidation state. Copper naphthenate exerts a unique influence over cure rate in redox systems and is used widely to delay cure and reduce exotherm development during the cross-linking reaction. 

Sulfenamide accelerators generally requite less fatty acid because they release an amine during the vulcanization process which acts to solubilize the zinc. Guanidines and similar amine accelerators also serve to both activate and accelerate vulcanization. 

Epoxy (Anhydride-Cured) Epoxy resins may be crosslinked with various anhydrides by using a tertiary amine accelerator and heat. These cured polymers generally have good chemical resistance especially to acids. 

The complex formation between hydroperoxides and HALS derivatives proposed for the preceding reaction was recently postulated by two different groups of investigators. First, Carlsson determined a complex formation constant for +00H and a nitroxide on the basis of ESR measurements—. Secondly, Sedlar and his coworkers were able to isolate solid HALS-hydroperoxide complexes and characterize them by IR measurements. The accelerated thermal decomposition of hydroperoxides observed by us likewise points to complex formation. It is moreover known that amines accelerate the thermal decomposition of hydroperoxides-. Thus Denisov for example made use of this effect to calculate complex formation constants for tert.-butyl hydroperoxide and pyridineitZ.. 

Mixing of propylene oxide and epoxy resin in a waste bottle led to an explosion, probably owing to the polymerisation of the oxide catalysed by the amine accelerator in the resin. 

Tertiary amine accelerated polymercaptan/ epoxy systems, 10 410 Tertiary amine-carbonate technology,... 

On the other hand, addition of tertiary amines accelerated hydrogenation of some compounds over Raney nickel [6I. In hydrogenation of halogen derivatives over palladium [62] or Raney nickel [63] the presence of at least one equivalent of sodium or potassium hydroxide was found necessary. 

Reactivity of Amine Accelerators with Anhydride-Epoxy Resin Systems ... 

Anhydrides generally provide pot lives of days or months and cure usually at 100-180°C with very little exotherm. Tertiary amines accelerate the time for gelation but still require the elevated temperature cure to obtain optimum properties. Anhydrides usually give brittle products but the addition of polyether flexibilizing groups yields more elastomeric products [44]. 

A tertiary amine is often used as an accelerator in primary amine systems to correct for these problems and to adjust the rate of cure. Ortho-(dimethylaminomethyl) phenol, DMP-30, and tris-(dimethylaminomethyl) phenol, DMP-10, are common commercial tertiary amine accelerators. 

EMI cured epoxy adhesive formulations are claimed to have outstanding adhesion to metals, and for this reason it is added as a co-curing agent in many compositions. It is an excellent anhydride accelerator providing higher thermal resistance than typical tertiary amine accelerators. 

When formulated into one-component adhesive systems, the product is stable when stored for 6 months to 1 year at room temperature. It will then cure when exposed to 145 to 160°C for about 30 to 60 min. Since the reaction rate is relatively slow at lower temperatures, the addition of 0.2 to 1 percent benzyldimethylamine (BDM A) or other tertiary amine accelerators is common to reduce cure times or cure temperatures. Other common accelerators are imidazoles, substituted urea, and modified aromatic amine. 

A-Nitrosamines in rubber products are by-products of the reactions taking place during the vulcanization of rubber mixtures [80]. They are formed from some chemical compounds such as secondary amines (accelerators, antioxidants) via nitrosation by nitrogen oxides present in the surrounding air. These reactions occur inside the rubber product and on its surface. The resulting A-nitrosamines from the interior of the rubber can diffuse to the surface of the article, and then to the environment or media in which the product is used. A-Nitrosamines can also be incorporated in the rubber mixture by contamination of raw materials during preparation. 

The effect of inhibitor, peroxide, initiator and amine accelerator on the rate of polymerization of poly(methyl methacrylate) slurries has been studied ( 5, O. Time required to reach the exotherm indicates aromatic peroxides, especially -chlorobenzoyl peroxide, to be the most efficient initiators. Although polymerization in the presence of this compound and N,N-dimethyl-2 toluidine (DMPT) is more rapid initially, it is slower after the exotherm than is a system employing BP-DMPT. Polymerization using the latter initiator-accelerator gives resins with lower residual monomer. 

Many initiator-accelerator systems that contain accelerators other than amine have been suggested for vinyl pol3rmerization, but only a few have been employed in dental resins. Substitution of p-toluenesulfinic acid, alpha-substituted sulfones and low concentrations of halide and cupric ions for tertiary amine accelerators, yields colorless products (43-48). Most of these compounds have poor shelf-life. They readily oxidize in air to sulfonic acids which do not activate polymerization. Lauroyl peroxide, in conjunction with a metal mercaptide (such as zinc hexadecyl mercaptide) and a trace of copper, has been used to cure monomer-pol3rmer slurries containing methacrylic acid (49-50). Addition of Na salts of saccharine to monomer containing an N,N-dialkylarylamine speeds up pol)rmerization (51). 

This problem doesn t exist for the main use of BP, which is in aromatic amine accelerated curing at ambient temperature. 

On the Mode of Amine-Accelerated Osmium Tetroxide Addition. . 23... 

The mechanism of the AD reaction, discussed in the limited context of what exact events take place during the chiral amine accelerated osmium tetroxide addition to alkenes, has been a subject of passionate debate for a number of years. The controversy is mostly concerned with two aspects of the alkene addition step in the AD process the exact mechanism of the amine-accelerated osmium... 

Despite considerable efforts, it has proven difficult to distinguish between these two mechanisms, partly because the (3-1-2) and (2-1-2) pathways are kineti-cally indistinguishable. Experimental support for a multi-step mechanism primarily stems from two experimental areas non-linear Eyring plots and analysis of the electronic effects in the amine acceleration, whereas theoretical studies of... 

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