Polyurethanes containing phosphorus

Whilst rigid closed-cell polyurethanes are excellent thermal insulators they do suffer from a limited and often unsatisfactory level of fire resistance, even in the presence of phosphorus-containing and halogen-containing fire retardants. Considerable promise is now being shown by the polyisocyanurates, which are also based on isocyanate chemistry. 

Lee, F. T., Green, J., and Gibilisco, R. D., Recent developments using phosphorus-containing diol as a reactive combustion modifier for rigid polyurethane foams 3, J. Fire Sci., 1984, 2, 439-453. 

Yanchuk, N. I., Fireproof phosphorus-containing polyurethanes, Khim. Technol. (Kiev), 1981, (1), 56-58. 

Polyether dendrimers, phosphorus-containing dendrimers, and polyurethane dendritic wedges also have been characterized by MALDI-TOF. 

Among phosphorus-containing additive flame-retardants, phosphates are mostly applied as secondary plasticizers in formulations of flame-retarded plasticized PVC. Other additive agents are admixed with natural and synthetic rubbers, polyester and epoxy resins, polyurethane foams, polystyrenes and polyethylenes, etc. 

Phosphorus-containing reactive flame-retardants are mainly phosphonates or phosphates with hydrogen atoms which can be substituted by hydrocarbon groups, so that they are capable of bonding to molecules of the matrix polymer. A notable example is the series of phosphorus-containing polyols. Their alcoholic hydroxyl groups are involved in a polyaddition reaction of the polyurethane foam production. 

Scheme 3.2 Synthesis of phosphorus-containing polyurethanes via transesterification of diesters of H-phosphonic acids with urethane diols.

Polyurethane foams having high combustion resistance have been prepared from phosphorus-containing polyols, used as hydroxyl-containing components [103],... 

Rigid polyurethane foams have been synthesized from industrial raw materials and phosphorus-containing flame retardants, obtained by the interaction of dialkyl H-phos-phonates with amino alcohols. The phosphorus-containing compounds 1 and 2 are used as modifiers [105]. During polyurethane synthesis, both modifiers speed up the times for foaming, gel formation, and surface drying, and decrease the time for foam growth. 

The phosphorus-containing polyacroleine obtained in this way is used as an additive to paints, polyurethanes, and epoxy resins in order to increase their combustion resistance. 

The polyurethane industry is searching for a more environmentally acceptable alternative to pentabromodiphenyl ether, which has been banned in Europe and voluntarily withdrawn in the United States. The preference appears to be in favor of phosphorus-containing materials. 

Several classes of P- and N-containing polymers have been reported in literature. These include polybenzimidazoles, polyester-imides, polyamide-imide, polyanhydride-imides, polyurethanes, polyamides, and polymaleimide-amines. Heretofore, phosphorus-containing bisimide resins have received little attention. Bisimide monomers, which cure by addition-type polymerization without the elimination of volatile products, are suitable as matrix resins for fabrication of graphite-fabric reinforced composite materials. 

Polyurethanes polyols containing a halogen, phosphorus compounds, and both phosphorus and halogen, organophosphates. 

The phosphorus-containing polyurethane-semicarbazides VIII are obtained in two steps (i) preparation of the phosphorus-containing prepolymer VII and (ii) chain extension by isophthalic or 0-substituted phenylthiophosphoric acid dihydr azide ... 

Goncharova L B, Grekov A P, Batjaeva S I and IVoev K D (1986) Phosphorus-containing cation-active polyurethane semicarbazides, UkrKhim Zh 52 1100-1104 (in Russian). 

Commercially available flame retardants include chlorine- and bromine-containing compounds, phosphate esters, and chloroalkyl phosphates. Recent entry into the market place is a blend of an aromatic bromine compound and a phosphate ester (DE-60F Special) for use in flexible polyurethane foam (8). This paper describes the use of a brominated aromatic phosphate ester, where the bromine and phosphorus are in the same molecule, in high temperature thermoplastic applications. 

Shao, C. H., Huang, J. J., Chen, G. N., Yeh, J. T., and Chen, K. N., Thermal and combustion behaviors of aqueous-based polyurethane system with phosphorus and nitrogen containing curing agent, Polym. Degrad. Stab., 1999, 65, 359-371. 

Sivriev, C. Zabski, L. Flame retarded rigid polyurethane foams by chemical modification with phosphorus-and nitrogen-containing polyols. Fur. Polym. J. 1994, 30, 509-514. 

The volume leaders among fire retardants with 35 million pounds were the three phosphate plasticizers for PVC tricresyl phosphate, cresyl diphenyl phosphate and triphenyl phosphate. The remaining 6 million pounds were made up of octyl diphenyl phosphate, tributyl phosphate, tri(dibromopropyl) phosphate, tri(dichloropropyl) phosphate and tri-(chloroethyl) phosphate. Polymeric phosphorus and phosphorus halogen-containing additives are used in concentrations of 3-25 p.p.h. in polyesters, flexible and rigid polyurethane foam, and phenolics. 

The fire resistance of polyurethanes is based on the introduction of flame retardant compounds including polyols, containing chlorine, bromine or phosphorus in their structure. The polyols containing chlorine, bromine or phosphorus are linked chemically in the polyurethane structure and lead to self-extinguishing polyurethanes, with a permanent flame retardancy. 

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