Amines accelerated polymerization

The mechanism of the polymerization of NCA with tertiary amine is still controversial. Mori and Iwatsuki claim that the true initiator is the primary amino group formed by hydrolysis of the NCA with contaminated water and that tertiary amine forms a complex with the NCA and accelerates the addition reaction37 . Harwood et al. confirmed the propagating carbamate by NMR in polymerization initiated with a strong base37 . The successive addition of NCA to the polymer end catalyzed with a strong base affords an alternative procedure for the synthesis of block copolypeptides. Block copolypeptides of poly(oxyethylene) were prepared by triethyl amine catalyzed polymerization of NCA in the presence of poly(oxyethylene)bis-eMoroformate38 . 

Polymerization of monosilicic acid has a minimum rate at pH about 2. The reaction is approximately second-order above that pH, and third below. In the latter region there is also fluoride catalysis From studies in methanolic solution it is clear that water, ammonia and amines all accelerate polymerization, probably as proton acceptors rather than as nucleophiles. The kinetics are in an early stage of development. 

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). 

Ethers and amines accelerate initiation to a much greater degree than propagation. Therefore, their effect on the rate of overall polymerization, initiation and propagation, is more pronounced than would be expected from consideration of propagation alone... 

Humphreys, of the Loctite Corporation, reported on the chemistry of accelerators for curing anaerobic adhesives. He showed that the reaction between N,N-dimethylaniline derivatives and cumene hydroperoxide is relatively slow even at lOO C. He concluded that the accelerated polymerization of anaerobic adhesives of ambient temperatures caused by cure systems containing combinations of tertiary aromatic amines, hydroperoxides, and sulfonimides does not result from the hydroperoxide-amine reaction. 

Synonyms N,N-dimethyl-p-toluidine 4-(dimethylamino)toluene p-N,N-trimethylaniline N,N-4-trimethyl-benzenamine Uses amine accelerator for the polymerization of e.g. dental methacrylic restorative materials A... 

Uses amine accelerator for the polymerization of e.g. dental acrylic-composite restorative materials... 

To prepare an acrylic denture base, the general technique is to use dispersions of the polymer powder in acrylic monomer to form a dough or a slurry (the latter in the case of "pour-type" denture base materials) which are conveyed to a mold holding the teeth in proper array for production of the denture. Polymerization may be initiated by thermal decomposition of peroxides or by room temperature cures using amine accelerators in redox type catalyst systems. 

Possible impurities of the tertiary amine include primary and secondary amines. The presence of aniline slows the reaction, while the presence of A-methylaniline actually accelerates the polymerization [51]. As the secondary amine may be formed during polymerization (especially in the presence of water) reaction kinetics may be complicated. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Avoid contamination with combustible materials, various inorganic and organic acids, alkalies, alcohols, amines, easily oxidizable materials such as ethers, or materials used as accelerators in polymerizations reactions Stability During Transport Extremely explosion-sensitive to shock, heat and friction. Self-reactive Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Not pertinent inhibitor of Polymerization Not pertinent. 

Finally, it should be noted that cationic polymerizations are very sensitive to impurities. These can act as cocatalysts, accelerating the polymerization, or as inhibitors (e.g., tertiary amines) they can also give rise to chain transfer or chain termination and so cause a lowering of the degree of polymerization. Since these effects can be caused by very small amounts of impurities (10 mol% or less), careful purification and drying of all materials and equipment is imperative. 

The acceleration of the initial stage of the epoxy compound polymerization under the action of the TA in the presence of the primary amine is explained by the role of the proton donor of primary proton amine activating the epoxy ring. The initial polymerization rate increases linearly with increasing concentration of the primary amine 46). 

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