Urethane catalysts

Monofunctional, cyclohexylamine is used as a polyamide polymerization chain terminator to control polymer molecular weight. 3,3,5-Trimethylcyclohexylamines ate usehil fuel additives, corrosion inhibitors, and biocides (50). Dicyclohexylamine has direct uses as a solvent for cephalosporin antibiotic production, as a corrosion inhibitor, and as a fuel oil additive, in addition to serving as an organic intermediate. Cycloahphatic tertiary amines are used as urethane catalysts (72). Dimethylcyclohexylarnine (DMCHA) is marketed by Air Products as POLYCAT 8 for pour-in-place rigid insulating foam. Methyldicyclohexylamine is POLYCAT 12 used for flexible slabstock and molded foam. DM CHA is also sold as a fuel oil additive, which acts as an antioxidant. StericaHy hindered secondary cycloahphatic amines, specifically dicyclohexylamine, effectively catalyze polycarbonate polymerization (73). 

The most common catalyst used in urethane adhesives is a tin(lV) salt, dibutyltin dilaurate. Tin(IV) salts are known to catalyze degradation reactions at high temperatures [30J. Tin(II) salts, such as stannous octoate, are excellent urethane catalysts but can hydrolyze easily in the presence of water and deactivate. More recently, bismuth carboxylates, such as bismuth neodecanoate, have been found to be active urethane catalysts with good selectivity toward the hydroxyl/isocyanate reaction, as opposed to catalyzing the water/isocyanate reaction, which, in turn, could cause foaming in an adhesive bond line [31]. 

The unblocking temperature usually refers to the temperature at which the blocked urethane system must be heated for 30 min in order to achieve cure. The reaction can be accelerated by curing at higher temperatures and/or by the addition of catalyst, as shown in Fig. 6 [62]. Common urethane catalysts like dibutyltin dilaurate are known to decrease the unblocking temperature. 

This structure has superior water-resistant properties in comparison to conventional polyols used for PU synthesis. Room temperature cures are easily obtained with typical urethane catalysts. Short chain diols, fillers and plasticizers may also be used in their formulations in order to vary physical properties. Formulations usually with NCO/OH ratio of 1.05 are used for this purpose. Such urethanes are reported to be flexible down to about -70 °C. HTPB is regarded as a work horse binder for composite propellants and PBXs. HTPB also successfully competes with widely used room temperature vulcanizing (RTV) silicones and special epoxy resins for the encapsulation of electronic components. HTPB-based PUs are superior in this respect as epoxy resins change their mechanical properties widely with temperature. 

The PU compositions can be prepared by dispersing the mass ABS resin in the reactants used to prepare the PU and then contacting the resultant dispersion with the other urethane reactants under conditions sufficient to form the PU. The reaction can be accelerated by the addition of suitable urethane catalysts, for example by tertiary amines (33). When the PU is prepared by reactive extrusion, the ABS resin may be added already initially along with the urethane-forming reactants. This toughened PU is particularly useful in making structural automotive body parts and housings for electrical appliances. 

Example (1) Unsaturated monoalcohol (acryloesterol) and styrene monomer are reacted with a polyisocyanate in the presence of a urethane catalyst and a radical polymerization catalyst to form hybrid resins (52). Styrene monomer acts as a crosslinker and at the same time, acts also as a reactive diluent. The trade name of a commercial product of such systems is Arimax (Ashland Chemical) (107). 

In the case of urethane-modification, two kinds of catalysts, i.e., urethane-formation catalysts and isocyanate-trimerization catalysts, are usually used. Major trimerization catalysts are listed in Table 11 and major urethane catalysts are listed in Tables 8 through 10. 

The structure of the catalytic species was not established at the present time but indications are that the Increased catalytic activity Is associated with the formation of chloro complexes of dibutyltln monolaurate. Dibutyltin dichloride is very weak urethane catalyst as was previously established (2). 

DMAMP-SO . [Angus] 2-Dimethyl-amino-2-methyl-l-propanol solubilizer, emulsifier, corrosion inhibimr, urethane catalyst, synthesis api cs. 

In each case, a solution of the desired dlol in 2-hydroxyethyl acrylate was charged to the addition funnel and the isophorone diisocyanate, inhibitor and urethane catalyst were charged to the reaction flask with the water bath in place. The addition took one hour and after a two hour hold at room temperature, the appropriate trifunctional branching agent (TBA) was added. when the amine functional TBA was used, a 50 50 solution of the TBA in the... 

Urethane Catalyst Free Radical Inhibitor Proprietary Reactive Diluent... 

Organometallic complexes of Sn, Bi, Hg, Zn, Fe, and Co are all potent urethane catalysts, with Sn carboxylates being the most common. Hg catalysts have long induction periods that allow long open times. Hg catalysts also promote the isocyanate hydroxyl reaction much more strongly than the isocyanate water reaction. This allows their use in casting applications where pot life and bubble-free parts are critical. Bismuth catalysts are replacing mercury salts in numerous applications as the mercury complexes have come under environmental pressure. 

Chem. Descrip. 2-Dimelhylamino-2-methyl-1-propanol CAS 7005-47-2 EINECS/ELINCS 230-279-6 Uses Neutralizer tor waterborne systems amine solubilizer tor resins in aq. coatings emulsifier tor waxes vapor-phase corrosion inhibitor urethane catalyst titanate solubilizer raw material for synthesis add salt as delayed cure catalyst in permanent press resins Properties APHA100 max. color misc. with water sp.gr. 0.95 dens. 7.9 Ib/gal vise. (Gardner) A-A2 f.p. -20 C b.p. 98 C (760 mm) flash pt. (TOC) 150 F pH 11.6 (0.1N aq.) 80% act. 

Various catalysts are used to prepare polyurethane at a relatively low temperature and with a much faster rate of polymerisation than would be the case with an uncatalysed reaction. Catalysts may be classified into two broad categories namely, amine (basic) compounds and organometalhc complex compounds. Tertiary amine is stiU one of the most frequently used urethane catalysts. Commonly used amine catalysts are triethylenedi-amine (TEDA), l,4-diazabicyclo[2.2.2]octane (DABCO), triethylamine (TEA), dimethylethanolamine (DMEA) and dimethylcyclohexylamine (DMCHA). The catalysis mechanism of tertiary amine catalysed urethane reaction involves complexation of the amine with isocyanate groups, followed by reaction of the complex with alcohol to produce polyurethane. A list of catalysts used in polyurethane preparation is given in Table 6.4. 

Recently Saunders (39) conducted a detailed study of emulsion latices made from methyl ethyl ketoxime-blocked lEM (lEM-MEKO). Compositions investigated were styrene/-butyl acrylate/IEM-MEKO, styrene/butyl aerylate/IEM-MEKO latex formulated with active hydrogen compounds and styrene/butyl acrylate/IEM-MEKO copolymerized with vinyl acids or hydroxy monomers. The effect of urethane catalysts on the deblocking/curing reaction was also studied. 

Bases are the most important group of urethane catalysts used in commercial practice, and their properties have been studied in depth and various systems are well established. 

The predominant configuration is trans 1,4 60%, with approximately 20% cis 1,4 and 20% vinyl 1 2, prepared by emulsion polymerization and with predominantly primary terminal hydroxyl groups of the allylic type. Hydroxyl functionality varies from 2-4 to 2-6 and gives high reactivity with aromatic diisocyanates. Room temperature cures are easily obtainable with typical urethane catalysts. Short-chain diols, fillers and process oils can also be used in their formulation to vary physical properties. 

---