The choice of polyurethane catalyst affects the reactivity of the entire foaming system and the selectivity of some individual reactions described above. The reactivity of the foaming system is expressed by the activation time of the system, the curing process, demoulding or curing time.
Changes in reaction selectivity as a function of changes in catalyst choice affect the balance of reactions that occur, the type and sequence of polymer chains formed, and the fluidity of the foaming system, thereby affecting the processing and physics of the final foam performance.
The commonly used catalysts for urethane foaming are tertiary amines, quaternary amines, amine salts and metal nucleic acid salts (usually SnII, SnIV or K+). Tertiary amines are used to promote gelling. Foaming and crosslinking reactions. Lime salts and thermosensitive amines, such as diazobicycloundecane, are used to provide delayed action. Metal formates strongly influence the gelation reaction.
Stannous compound (SnⅡ) is low in cost, but it is easily hydrolyzed and unstable. Typical use is where individual streams can be metered, such as soft briquettes.
Tin compounds (SnIV) are not easily hydrolyzed and can be incorporated into systems such as flexible molding and rigid foaming. For example, a class of specific compounds such as quaternary amine, potassium nucleic acid, tris(dimethylaminomethyl)phenol and 2,4,6-tris[3-(dimethylamino)n-propyl]hexahydro-s-tribarrier Trimerization is highly selective.
Polyurethane foams are characterized by a variable polymer structure to meet a wide range of application needs. This structural difference is not only due to the different isocyanates and polyols used as raw materials, but also to the different reactions that these raw materials undergo. These reactions are strongly influenced by the type and amount of polyurethane catalyst used.
