Diisocyanate Dispersion

Subsequent chlorination of the amide takes place ia a two-phase reaction mixture (a dispersion of diamide ia hydrochloric acid) through which a chlorine stream is passed. The temperature of this step must be maintained below 10°C to retard the formation of the product resulting from the Hofmann degradation of amides. Reaction of the A/,A/-dichloroamide with diethylamine [109-89-7] ia the presence of base yields /n j -l,4-cyclohexane-bis-l,3-diethylurea (35), which is transformed to the urea hydrochloride and pyroly2ed to yield the diisocyanate (36). 

Water-borne polyurethane coatings are formulated by incorporating ionic groups into the polymer backbone. These ionomers are dispersed in water through neutrali2ation. The experimental 1,12-dodecane diisocyanate (C12DI Du Pont) is especially well suited for the formation of water-borne polyurethanes because of its hydrophobicity (39). Cationomers are formed from IPDI, /V-methyIdiethan olamine, and poly(tetramethylene adipate diol)... 

Polyurethane dispersions (PUD s) are usually high-performance adhesives based on crystalline, hydrophobic polyester polyols, such as hexamethylene adipate, and aliphatic diisocyanates, such as methylene bis(cyclohexyl isocyanate) (H12MDI) or isophorone diisocyanate (IPDI). These PUD s are at the more expensive end of the waterborne adhesive market but provide excellent performance. 

The block lengths and the final polymer molecular weight are again determined by the details of the prepolymer synthesis and its subsequent polymerization. An often-used variation of the one-prepolymer method is to react the macrodiol with excess diisocyanate to form an isocyanate-terminated prepolymer. The latter is then chain-extended (i.e., increased in molecular weight) by reaction with a diol. The one- and two-prepolymer methods can in principle yield exactly the same final block copolymer. However, the dispersity of the polyurethane block length (m is an average value as are n and p) is usually narrower when the two-prepolymer method is used. 

Composite rocket propellants are two-phase mixtures comprising a crystalline oxidizer in a polymeric fuel/binder matrix. The oxidizer is a finely-dispersed powder of ammonium perchlorate which is suspended in a fuel. The fuel is a plasticized polymeric material which may have rubbery properties (i.e. hydroxy-terminated polybutadiene crosslinked with a diisocyanate) or plastic properties (i.e. polycaprolactone). Composite rocket propellants can be either extruded or cast depending on the type of fuel employed. For composite propellants which are plastic in nature, the technique of extrusion is employed, whereas for composite propellants which are rubbery, cast or extruded techniques are used. 

Polyurethane is also used as a foam, mostly in sheet form as an underlay or middle layer for example in fruit bins. The following starting materials for polyurethane foam can be used polyester with hydroxyl end groups made from adipic acid, diethylene glycol, trimethylol propane as well as polyether based on ethylene oxide and/or propylene oxide with free hydroxyl groups in combination with 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. Stabilizers, dispersants and amines (as catalysts in amounts up to 1.2 %) can be used. 

The dynamic mechanical properties of three epoxy resins cured with diphenyl-methane diisocyanate (MDI) are shown in Fig. 15. Since these resins consist of many bulky cyclic structures, Tg (a-dispersion) is above 200 °C and the transition region is wide. In the DEN 431 —L-MDI resin, Tg is higher than 300 °C. The resin is expected to be highly heat-resistant51). 

Bonnet [3] prepared aqueous dispersions of bitumen and asphaltenes using the urethane reaction product of 4,4 -diphenylmethane diisocyanate and PolyBd diol. 

Polyurethane [117] and polyester [118] particles have also been prepared by the dispersion polyaddition of ethylene glycol (EG) and toluene diisocyanate (TDI) in paraffin, and the polycondensation of acid and ester at a high polymerization temperature, respectively. Table 3 provides an overview of microspheres of monomers other than vinyl monomers obtained by dispersion polymerization. 

Composite rocket propeiiants. This type of propellant contains two-phase mixtures with a aystalhne oxidizer in a polymeric fuel or binder matrix. The finely dispersed powder of ammonium perchlorate suspended in a fuel is the oxidizer. The fuel is a plasticized polymeric material such as hydroxy-terminated polybutadiene cross-linked with a diisocyanate (rubber ts e) or carboxy-terminated polybutadiene (plastic type) [4]. 

Polyurethane pre-polymer or thermoplastic polyurethanes are prepared by the reaction of polyester or polyether diols with diisocyanates. The reaction can be conducted in bulk, in a solvent, or in an aqueous solution or dispersion. Unless the reaction is carried out at an elevated temperature a catalyst is required. Organotin compounds are the prime catalyst for this reaction. 

Special methods of incorporation fillers are frequently pre-dispersed in polyol (for better mechanical properties) or plasticizers (to dry while dispersing) hydroxyapatite was modified by reaction with hexamethylene diisocyanate " ... 

The amine-based Henry reaction catalyst was encapsulated via the interfacial polymerization of oil-in-oil emulsions. PEI was encapsulated by dispersing a methanolic PEI solution into a continuous cyclohexane phase. Upon emulsification, 2,4-tolylene diisocyanate (TDI) was added to initiate crosslinking at the emulsion interface, forming polyurea shells that contain free chains of PEI. The microcapsules crenate when dry and swell when placed in solvents such as methanol and dimethylformamide, suggesting a hollow capsule rather than a solid sphere formation. The catalyst loading was determined to be 1.6 mmol g . ... 

MW of 120,000 daltons) [61]. In fact the nonreactive NAD presented before (structures 6.15 and 6.16) are poly ethers with extended molecular weight, the chain extender being the epoxy resins or the diisocyanates (or polyisocyanates). As in the case of macromers, it is possible to obtain high, solid stable polymeric dispersions, of low viscosities, with nonreactive NAD too. 

PHD polymer polyols are a special class of filled polyols developed successfully by Bayer, PHD being the abbreviation of the German name polyharnstoff dispersion or polyurea dispersions [67-69]. PHD polyols contain organic urea, oligomeric or polymeric polyurea, finely dispersed in liquid polyether polyols [67-73]. The difference between PHD polyols and graft polyether polyols is the different nature of the solid polymer dispersed (it is a heterocatenary polymer - polyurea - instead of carbocatenary polymer) which is obtained by another synthetic procedure (polyaddition reaction between a diisocyanate and a diamine instead of radical polymerisation). The reaction between the diisocyanate and the diamine, takes place in situ (reaction 6.19), in liquid poly ether. The resultant polyurea being insoluble in polyether, precipitates in the form of very fine particles ... 

A small part of the -NCO groups of diisocyanate reacts with the terminal hydroxyl groups of polyethers and forms a block copolymer structure, having a polyurea segment chemically linked to a polyether segment, which plays the role of a nonaqueous dispersant and assures the excellent stability of the resulting polyurea dispersion (reaction 6.20) [67, 68]. 

The concentration of this hybrid structure (polyether block linked to a polyurea block) is low, but it is enough to assure a good stability of the dispersion. This very reactive system is based on the big difference in reactivity between primary amines and hydroxyl groups and the -NCO groups of the diisocyanate. Thus the -NCO group reacts 3300 times more rapidly with primary amines than with secondary hydroxyl groups and around 1000 times more rapidly than with the primary hydroxyl groups. 

---