Delayed action catalysts

Hydroxy group containing tertiary amines are also used because they become incorporated into the polymer stmcture, which eliminates odor formation ia the foam (3). Delayed-action or heat-activated catalysts are of particular interest ia molded foam appHcations. These catalysts show low activity at room temperature but become active when the exotherm builds up. In addition to the phenol salt of DBU (4), benzoic acid salts of Dabco are also used (5). 

Delayed action catalysts are used in certain two-component adhesives systems but will not be discussed here. A review of delayed action catalysts can be found elsewhere [32]. 

The first application of pyrazino[2,3-6]pyrazines as vulcanization accelerators for rubber copolymerization has been reported in CHEC-I. Some new pyrazino[2,3-A]pyrazine derivatives are in use as electrophotographic developers <90JAP(K)2135365) and light-resistant fluorescent polymers <89JAP(K)0l 153750). Some alkylsubstituted decahydropyrazino[2,3-6]pyrazines are suitable as delayed-action catalysts for the preparation of urethanes <83USP452839l>. Other pyrazinopyrazine derivatives are reported to have inhibitory effects on tomato spotted wilt virus <83MI 719-01). 

Recently, delayed-action catalysts have been used to adjust reactivity profiles for rigid and flexible molded foams (38). Some of these catalysts are shown in Table 10. 

Because of environmental concerns about using chlorofluorocarbon (CFC) blowing agents, methylene chloride is being used as a blowing agent. A number of catalysts have been developed that are particularly compatible with methylene chloride. Several of these new catalysts work on the delayed-action principle to avoid splitting of the foams (22). 

Delayed-action catalysts have been made successfully. Buffered amine catalysts, where the activity of the amine has been reduced by the presence of an acid, have also been used. Acidic materials can be used to retard the urethane reaction. Hydrogen chloride and benzoyl chloride have been used in combination with amine-type catalysts to control reaction rates. A small percentage of acid can increase foaming time from 2.2 to 6 minutes (20). 

Complexes of organotin with amidines have been found to be excellent catalysts for the preparation of polyurethane foams, which do not have the disadvantage of any amine odor and, in addition, delayed onset of the isocyanate-hydroxyl reaction An example of a mercapto-delayed organotin catalyst is 2,2,4,4-tetrakis(alkyl)- l,3,2,4-dithia-stannetane.55 Amine salts of amino acids, tertiary amino acids, and tertiary amino acid-nitrile compositions, have been found to be effective as delayed action catalysts for polyurethane synthesis. They are particularly effective when used in combination with an organometallic compound, such as an organotin. ... 

Uses Gelation catalyst for rigid, flexible, and semi-flexible molded slabstock, coatings, sealants, elastomers, and shoe soles Features Very strong with delayed action Properties Insol. in water sp.gr. 1.18 vise. 400 mPa-s flash pt. (PMCC) 85 C... 

Chem. Descrip. Proprietary blend ot delayed-activity tin and a tert. amine Uses Gelation catalyst tor flexible molded and rigid PU, PU coatings, elastomers, shoe soles Features Delayed-action... 

Chem. Descrip. Organotin Uses Catalyst for PU coatings, adhesives, sealants Features Provides delayed action catalysis of isocyanate/polyol reaction Properties Lt. yel. liq. sol. in alcohols, org. soivs., insol. in water sp.gr. 1.11 vise. 33 cps f.p. -23 C decomp. pt. 255 C flash pt. (PMCC) 130 C 17.5% total tin... 

Chem. Descrip. Polycat DBU with an organic acid blocker CAS 6674-22-2 EINECS/ELINCS 229-713-7 Uses Catalyst for PU coatings, rigid, elastomeric, shoe sole applies. Features Delayed-action heat-activated provides exc. back-end cure Prqrethes Liq. sol. in water sp.gr. 1.073 vise. 433 cps vapor pressure 1.29 mm Hg (38 C) f.p. < -78 C flash pt. (CC) > 94 C Polycat SA-1/10 [Air ProdsVPerf. Chems.]... 

Dabco BL-17 Delayed action tertiary amine blowing catalyst. APCI... 

To make satisfactory CHDI-based polyurethanes the use of a catalyst is necessary, and in this instance a delayed action type was used, namely dicarbobutyloxy ethyl tin dichloride (trade name Akzo Chemie T220 ester tin dichloride ) at the concentration 0-01-0 03% by weight of the total reactants. 

Phencat 382 A delayed-action catalyst which is activated at typically 60-80. It offers up to a four-fold increase in pot-iife and reduced exotherm risk in isothermal RTM or press processes. 

It is possible to mould very large components because of the availability of delayed action catalysts. 

Application Delayed action catalyst for solvent-free polyurethane Chemical Composition Strongly acidic cation exchanger with... 

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. 

The selected team initially established a specific plan of investigation procedures for this occurrence. This strategy session listed priorities and necessary actions to ensure that all required information was obtained in a prompt manner. Needless delays in evidence collection were avoided by the use of this plan which helped to accelerate the rebuilding/restarting of the catalyst preparation area. 

The action of inhibitors is not so simply described, since they may act in a number of different ways. An inhibitor may slow a radical chain reaction by combining with the radicals nitric oxide functions in this way. In other cases, the inhibitor is consumed by combination with one of the reactants and only delays the reaction until it is used up. Some inhibitors may simply poison a trace of catalyst whose presence is unsuspected. 

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