Triethylenediamine catalyst

Catalysis is usually accompHshed through the use of tertiary amines such as triethylenediamine. Other catalysts such as 2,4,6-/m(/V,/V-dimethylaminomethyl)phenol are used in the presence of high levels of cmde MDI to promote trimerization of the isocyanate and thus form isocyanurate ring stmctures. These groups are more thermally stable than the urethane stmcture and hence are desirable for improved flammabiUty resistance (236). Some urethane content is desirable for improved physical properties such as abrasion resistance. 

In recent years there has been some substitution of TDI by MDI derivatives. One-shot polyether processes became feasible with the advent of sufficiently powerful catalysts. For many years tertiary amines had been used with both polyesters and the newer polyethers. Examples included alkyl morpholines and triethylamine. Catalysts such as triethylenediamine ( Dabco ) and 4-dimethyla-minopyridine were rather more powerful but not satisfactory on their own. In the late 1950s organo-tin catalysts such as dibutyl tin dilaurate and stannous octoate were found to be powerful catalysts for the chain extension reactions. It was found that by use of varying combinations of a tin catayst with a tertiary amine... 

Whilst reaction can take place in the absence of catalysts it is more common to use such materials as tetra-alkylammonium halides and tertiary amines such as triethylenediamine. A major side reaction leads to the production of isocyanurate rings, particularly in the presence of tertiary amines. 

Triethylenediamine (DABCO) and dibutyltin dilaurate (DBTDL) have been used as catalysts with concentrations of 0.25 and 0.06Z (w/w) on binder, respectively. 

A binder was obtained from an epoxynovolak resin, BPA/DC, BMI, dicyclopenta-diene, Zn acetate and dicumyl peroxide [94]. In a similar composition, BPA/DC prepolymer was used as curing and cyclotrimerization initiators and catalysts, catechol, triethylenediamine, Zn acetate and benzoyl peroxide are mentioned [95], Other compositions contain A1 acetylacetonate and a silicone resin [96], p-toluenesulfonic acid monohydrate and Zn octoate (for rapid curing) [97], or dicumyl peroxide and Zn octoate [98]. 

Epoxynovolak resin and BPA/DC-BMI prepolymer, tert.butyl peroxide and Zn acetate [106, 107] or 2-phenylimidazole and other catalysts [108] were filled with wollastonite. Carbon-fiber reinforced composites were obtained using a binder, which consisted of BPA/DC, BMI, an epoxynovolak, 2-ethyl-4-methylimidazole and an organic solvent [109]. A BPA/DC-BMI prepolymer in methylethylketone was mixed with middle-molecular-weight epoxide resin (Epikote 1001), 2-ethyl-4-methyl-imidazole, Zn acetate and triethylenediamine thermal shock resistant GRP was thus obtained [110]. 

Two-layered GRPs for copper clad laminates are obtained with one layer consisting of the three-component system (e.g. BPA/DC, BMI, brominated epoxide resin, Zn octoate and triethylenediamine in methylethylketone). The other layer has the usual epoxy matrix (brominated epoxide resin, dicyandiamide as a hardener and 2-ethyl-4-methylimidazole as curing accelerator) [119]. As similar two-layered laminate contains BPA/DC, BMI, epoxynovolak resin, Zn acetate and triethylenediamine in the first layer and BPA/DC only with the same catalysts in the second layer [120]. 

The technique of measuring maximum heat rise during reaction has been utilized as a measure of catalytic activity. In contrast to many kinetic measurements made in dilute solution, relatively concentrated solutions can be employed which more nearly represent practical foam manufacture. The isocyanate-water and isocyanate-hydroxyl reaction can be studied separately. This has been used extensively under the designation of the Wolfe test (74). The results of these tests demonstrate the very high activity of triethylenediamine for the isocyanate-water reaction. Likewise, this catalyst is the most active amine catalyst for the isocyanate-hydroxyl reaction, although less active than tin compounds. This test can also be used effectively for testing mixtures of catalysts. This is in accord with present commercial practice of using an amine—usually triethylenediamine —and a tin compound to achieve optimum results. 

Hostettler and Cox [141] reported relative reaction rates of phenyl isocyanate with ra-butanol, water, and diphenyl urea by various catalysts. Taking the rate of phenyl isocyanate with -butanol as 1, relative rates catalyzed by N-methylmorpholine (II), triethylamine, tetramethyl-1,3—butanediamine, triethylenediamine, tributyltin acetate, and dibutyltin diacetate are 40, 86, 260, 1200, 80,000, and 600,000, respectively. The relative rate with water when uncatalyzed is 1.1, while the relative rates catalyzed by N-methylmorpholine (II),... 

Furthermore, tertiary amines like triethylenediamine (DABCO) are also effective catalysts for isocyanate self-addition reactions, whereas organometal-lic catalysts are generally ineffective and tin compounds are particularly poor catalysts for these reactions [10]. 

DABCO catalyst (triethylenediamine, Air Products and Chemicals, Inc.) was purified by sublimation and stored in a desiccator. 

We have measured the synergism of dibutyltin dilaurate (DBTDL)-triethylenediamine catalyzed reactions of phenyl isocyanate with butanol and water at various concentrations of the tin and amine. As Tables I and II show, there is a lack of proportionality between the acceleration of the reaction and the concentration of the additives. If one assumes the tin catalyzed reaction is of second order and calculates the increase in rate constant due to the addition of amine co-catalyst, one finds that the addition of 0.02% amine based on isocyanate increases the rate of DBTDL catalyzed NCO-2-butanol by a factor of A.2. If one increases this amount of amine ten times, the resulting increase in the rate is only 5.30 times, while increasing the concentration of the amine by a factor of 100 results in an increase of the rate constant only by a factor of 7.1. 

Steric effects arise from structural interactions between substituents on the catalyst and the reactants that will influence their interaction. The importance of steric effects can be seen by comparing the activity for triethylenediamine to that of triethylamine. The structure of triethylenediamine (see Fig. 9) forces the nitrogens to direct their lone electron pairs outward in a less shielded position than is true of triethylamine. This results in a rate constant for triethylenediamine that is four times that of triethylamine at 23°C [1]. 

Triethylenediamine (1,4-Diaza-bicyclo [2.2.2]octane, Dabco) is increasingly used as a base a catalyst and a complexing agent for bromine as well as for organolithium compounds... 

Thus, it is the separation in time of the formation processes of the linear polymer and the intermolecular crosslinks that produces adhesive-bonded joints with low internal stresses. In the adhesive containing 20% of gel fraction but in which the crosslinks were formed using triallyl isocyanurate along with the polymer formation, the intem d stresses were substantially higher than in the adhesive containing ATG only (see Fig. 4.8b, curve 4). Increase of the crosslink formation rate by adding triethylenediamine, as catalyst of the reaction of the isocyanate groups with water, to the adhesive simultaneously with addition of ATG cdso increased the internal stresses (see Fig. 4.8b, curve 5). 

Triethylenediamine (l,4-diazabicyclo-2,2,2-octane, DABCO) n. This tertiary diamine, whose structure is shown below, is the most widely used amine catalyst for polyurethane foams, elastomers, and coatings. It is soluble in water and polyols. 

The tertiary amine-catalyzed reactions cause branching and cross-linking and are primarily used for polyurethane foam formation. They are used to accelerate the isocyanate-hydroxyl reaction and give off carbon dioxide. Triethylenediamine is the most prevalent of the tertiary amine catalysts used for polyurethane manufacture. 

PUs are formed as a result of a condensation or an adduction reaction between isocyanates and polyols [polyesters or polyethers with terminal hydroxyl (OH) groups, castor oil or tall oil]. If both components are more than difunctional, thermosetting end products are produced. Many auxiliary substances are also used in the manufacture of PU products. The hardening process can be modified by heat or with a catalyst [diamino diphenylmethane or meth-ylenedianiline (MDA), triethylenediamine, triethyl-amine, cobalt naphthenate or nickel salts]. Figure 1... 

Rapid growth of urethane technology can be attributed to the development of catalysts. Catalysts for the isocyanate-alcohol reaction can be nucleophilic (e.g., bases such as tertiary amines, salts and weak acids) or electrophilic (e.g., organometallic compounds). In the traditional applications of polyurethanes (cast elastomers, block foams, etc.) the usual catalysts are trialkylamines, peralkylated aliphatic amines, triethylenediamine or diazobiscyclooctane (known as DABCO), N-alkyl morpholin, tindioctoate, dibutyl-tindioctoate, dibutyltindilaurate etc. 

As mentioned in Section 8.4.3.1., the majority of hydroxy groups in a polyether triol are secondary groups and are comparatively unreactive towards isocyanates. It is therefore necessary to select a catalyst which favours the formation of urethane links relatively more than the formation of gas by the reaction of isocyanate and water. Tin compounds (e.g., stannous octoate and dibutyltin dilaurate) are particularly effective in this respect (cf.. Table 14.3) and are very widely used. In addition to the primary isocyanate-polyol and isocyanate-water reactions, several secondary reactions occur during the preparation of foam. As shown in Section 14.4, the final product may contain allophanate, biuret, isocyanurate and uretidione links. It will be appreciated that in a polymeric system, which is based on a diisocyanate, all of these links (except uretidione) represent points of branching or cross-linking. These secondary reactions are particularly favoured by tertiary amines (e.g., triethylenediamine and 4-dimethylaminopyridine) and these catalysts therefore contribute to the final cross-linking of the foam and hence to the achievement of, for example, a low compression set. Mixtures of tin compounds and tertiary amines are more... 

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