Polycarbodiimide foams

Therefore, the preparation of foams with a high percentage of closed cells or high-density foams is difficult. These foams are quite different from other isocyanate-based foams, e.g., urethane foams, isocyanurate foams and oxazolidone foams. 

The polyisocyanates used for preparing carbodiimide foams include TDl, TDl-based prepolymers, liquid-MDl oligomers and polymeric isocyanates. Many catalysts for producing carbodiimide foams have been disclosed in the patent literature. Some of these are shown in Table 13. 

Most of the catalysts are active only at elevated temperatures, but some are active at room temperature. Co-catalysts or accelerators have also been proposed. A carbodiimide-forming catalyst, 2,4,6-tris(dialkanolamino)-s-triazine was used for fs oducing carbodiimide foams. 

An example of the jx-oduction of carbodiimide foams is as follows (84). 50 parts of TDI and 0.5 parts of 2,4,6-tris(diethanolamino)-2-triazine were mixed and heated with agitation at lOO C. After 30 min from the start of mixing, carbon dioxide was generated and an exotherm was observed. After 60 min the foaming reaction was completed and the maximum temperature, about 200°C, was reached. 

An active co-catalyst system was proposed (83). The system is composed of 2,4,6-tris(diethanolamino)-s-triazine and l,3,5-tris(3-dimethylamino i opyl) hexahydro-s-triazine. This catalyst was used to jx-epare rigid carbodiimide foams from TDI without external heating. 

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Polycarbodiimide foams from polyisocyanates and 0.001-1% by weight of phospholine or phospholidine [82],... 

Isocyanate-based foams include polyurethane, polyisocyanurate, polyurea, polycarbodiimide, polyamide, polyimide, and polyoxazolidone foams. 

Polycarbodllmide n Polymers containing -N=C=N— linkages in the main chain, typically formed by catalyzed polycondensation of polyisocyanates. They are used to prepare open celled foams with superior thermal stability. Sterically hindered polycarbodiimides are used as hydrolytic stabilizers for polyester-based urethane elastomers. 

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