Carbodiimide foams

Modification of poly(carbodiimide) foams with polyols afford hybride foams containing urethane sections. However, the thermal stabilities of the poly (urethane carbodiimide) foams are lower. Using isocyanate trimerization catalysts, such as l,3,5-tris(3-dimethylaminopropyl)hexahydro-s-triazine, in combination with the phospholene oxide catalyst gives poly(isocyanurate carbodiimide) foams with improved high temperature properties. The cellular poly(carbodiimide) foams derived from PMDI incorporate six-membered ring structures in their network polymer structure. ... 

Modification of the poly(carbodiimide) foams, using polyols as comonomers, is possible, but the excellent thermal and flammability properties are reduced. Poly(carbodiimide isocyanurate) foams can also be continuously produced using 1,3,5-tris-(3-dimethylaminopropyl)-hexahydro-s-triazine as the cocatalyst. Other trimerization catalysts, such as potassium 2-ethylhexanoate and quaternary ammonium carboxylate (Dabco TMR 2) are also used as cocatalysts in the formation of poly(carbodiimide isocyanurate)... 

Thermosetting foams can be defined as foams having no thermoplastic properties. Accordingly, thermosetting foams include not only cross-linked polymer foams, but also some linear polymeric foams having no thermoplastic properties, e.g., carbodiimide foams and polyimide foams. These foams do not melt and turn to char by heating. 

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. 

A combination catalyst system comprising 2,4,6-tris(n-methylet-hanolamino)-s-triazine (I), and optionally, l,3,5-tris(3-dimethylaminopropyl)-hexahydro-s-triazine, bis(tributyltin) oxide or bis(triphenyltin) oxide was used for preparing carbodiimide foams. For example, a mixture of 0.5 g (I) and 50 g of tolylene diisocyanate was stirred at lOO C. The foaming started after 9 min and about 1 min after the foaming, the temperature in the vessel rose to 192 C the resulting foam occupied a volume of 800 ml (89, 90). 

NCO-terminated prepolymers have been used for producing carbodiimide foams (91). Bayer AG also developed carbodiimide foams (82). 

Some polymers are easier to foam than others. Indeed, it was not until methods were found to circumvent the inclusion of cells in the early history of the phenol formaldehyde polymer that it gained any commercial significance. The development of foamed phenolic resins only became important much later when a specific need arose to produce rigid foam with reduced flammability. This consideration also led to the development of polyisocya-nurate foams and carbodiimide foams. On the other hand, the polypropylene family of polymers, although having a tonnage far exceeding that of phenol formaldehyde resins, is... 

Expanded phenolic resin Poly(carbodiimide) foam Polyisocyanurate foam Expanded polystyrene, flame-retarded Fir-wood... 

Modification of cellular polymers by incorporating amide, imide, oxa2ohdinone, or carbodiimide groups has been attempted but only the urethane-modified isocyanurate foams are produced in the 1990s. PUIR foams often do not require added fire retardants to meet most regulatory requirements (34). A typical PUIR foam formulation is shown in Table 6. 

The mixture of (2S,3S,5S)-2-(2,6-dimethylphenoxyacetyl)amino-3-hydroxy-5-amino-l,6-diphenylhexane (100 g, 0.22 mol), 2S-(l-tetrahydro-pyrimid-2-onyl)-3-methyl butanoic acid methyl ester (44.8 g, 0.22 mol) and 750 ml DMF was cooled in an ice/water bath. N-Hydroxybenzotriazole (90.9 g, 0.67 mol), l-ethyl-3-[3-dimethylaminopropyl]carbodiimide (86 g, 0.45 mol) and triethylamine (62.5 ml, 0.45 mol) were added and the ice bath was removed, allowing the reaction mixture to stir with warming to room temperature for 5 hours. The mixture was diluted with 1000 ml of IPAC and quenched with 1000 ml of water. The mixture was shaken and separated, the aq. layer was extracted IPAC, the organics were washed with 10% HCI, solution of NaHC03 with 100 ml hexanes, then washed 500 ml water, and brine, dried over MgS04, filtered and concentrated to provide. (2S,3S,5S)-2-(2,6-dimethylphenoxyacetyl)amino-3-hydroxy-5-(2S-(l-tetrahydro-pyrimid-2-onyl)-3-methylbutanoyl)amino-l,6-diphenylhexane as a white foam. 

With regard to reactive flame-retardants, two routes can be followed to improve thermal stability and fire behavior of PU foams use of brominated or phosphorus-containing polyol or, for rigid foams, the introduction inside polymer backbone of more thermally stable structure than urethane, mainly isocyanurate, but also uretidione rings or carbodiimide.19... 

Saiki, K. Sasaki, K. Carbodiimide-modified polyisocyanurate foams Preparation and flame resistance. 

Protected neamine dimers were prepared using a Quest 210 parallel synthesizer. 5-Ethylcarboxyl-1,3,2, 6 -tetraazido-6,3, 4 -tri-6>-benzylneamine (0.0826 mmol/tube was dissolved in 1.5ml/tube containing CH2C12 distributed to each tube, which was then treated with MP-carbodiimide resin (1.15mmol/g) followed by 1,12-dodecylamine (0.0413 mmol/tube). Solutions were agitated 16 hours, filtered, concentrated, and dimers isolated as colorless foams. 

Cellular poly(carbodiimides) derived from polymeric isocyanate (PMDI) can be continuously produced using a phospholene oxide catalyst. As the component temperature is increased from 25 °C to 80 °C at a constant catalyst level, foam densities decrease with increasing component temperatures, with an expected corresponding decrease in compressive strength. The foam friability also decreases with increasing component temperature. 

The recent trend to abolish chlorofluorocarbon (CFC) blowing agents in rigid foam manufacture has prompted a new look on PMDI derived foams containing partial carbodiimide structure. Since carbon dioxide, generated in carbodiimide formation, can be used... 

Other types of isocyanate-based polymer foams, such as polyiso-cyanurate foams modified by oxazolidone, carbodiimide or imide linkages, have outstanding properties in flame retardance and fire endurance without the addition of any flame retardants... 

Preparation of Microcellular Foams. The major polyols for microcellular elastomers include aliphatic polyester diols having a molecular weight of about 1,000 to 3,000, and poly-epsilon-caprolactones. Poly(oxytetramethylene) glycols (PTMEG) can also be used. The polyisocyanates to be used for microcellular elastomers are TDI-prepolymers and liquid MDI, i.e., carbodiimide-modified MDI or urethane-modified MDI. Low-molecular-weight, active-hydrogen compounds such as chain extenders (difunctional compounds) and... 

The modification linkages include urethane, amide, imide, carbodiimide and oxazolidone linkages. A urethane-modified isocyanurate foam (trade name Airlite Foam SNB, Nisshinbo, Ind. Inc.) was first applied to the petrochemical industry as a seamless fire-resistant insulant in 1965 (39). 

A modification of isocyanurate foams by incorporating urethane-, carbodiimide- and imide groups has been reported (97). An example is as follows. The amounts of ingredients used are shown in parts by weight in parenthesis. 

Polyisocyanates are very rigid molecules and have only academic interest. Uretdione groups serve to modify certain polyurethanes. Isocyanurates form rigid foams (see also Section 35.5). Finally, the reaction of two isocyanate groups leads to carbodiimides (see also Section 28.1). 

These foams are characterised by higher thermal resistance, low smoke density rating, lower thermal condnctivity and higher friability than rigid PU foams. More recent chemical modification (cyclic imide groups, carbodiimide groups, etc.), of PIR foam provides relatively low friability and excellent thermal stability. 

PIR foams are produced by using standard PU foaming equipment. Unmodified PIR foams have a highly crosslinked structure, and therefore are extremely brittle. What did prove successful was to lower the crosslinking density of the foams by adding modifiers, which led to, modified polyisocyanurate foams such as [40] urethane-modified PIR foam, amide-modified PIR foam, imide-modified PIR foam, carbodiimide-modified PIR foam and oxazolidone-modified PIR foam. 

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