Diisocyanate difunctional

The use of hydroxyethyl (also hydroxypropyl) methacrylate as a monomer permits the introduction of reactive hydroxyl groups into the copolymers. This offers the possibility for subsequent cross-linking with an HO-reactive difunctional agent (diisocyanate, diepoxide, or melamine-formaldehyde resin). Hydroxyl groups promote adhesion to polar substrates. 

Step-growth polymers, the second major class of polymers, are prepared by reactions between difunctional molecules, with the individual bonds in the polymer formed independently of one another. Polycarbonates are formed from a diester and a diol, and polyurethanes are formed from a diisocyanate and a diol. 

Another class of hydrocarbon binders used in propints are the carboxy-terminated polybutadiene polymers which are cross-linked with either tris[l-(2-methyl)aziridinyl] phosphine oxide (MAPO) or combinations with phenyl bis [l -(2-methyl)aziridinyl] phosphine oxide (Phenyl MAPO). Phenyl MAPO is a difunctional counterpart of MAPO which makes possible chain extension of polymers with two carboxylic acid groups. A typical propint formulation with ballistic properties is in Table 11 (Ref 83) Another class of composites includes those using hydroxy-terminated polybutadienes cross-linked with toluene diisocyanate as binders. The following simplified equations illustrate typical reactions involved in binder formation... 

Singer S.M. and Allot M.T., Thermoplastic polyurethane elastomer based on a saturated hydroxyl terminated polyol, difunctional aromatic chain extender and 1,5-naphthalene diisocyanate, US Patent 5 599 874, 1997. 

The difunctional N-cyanourea compounds were found to polymerize into different polymeric materials at different temperatures. At room temperature, a linear polymer was obtained either from the polymerization of a di-N-cyanourea monomer or directly from the mixture containing a diisocyanate and cyanamide. At elevated temperature (>100°C), the di-N-cyanourea monomer, or the mixture of a diisocyanate and cyanamide, cross-linked to a rigid foam or flexible material, depending on the structure of the monomer. 

Chemistry of Polyurethanes. A binder system capable of many permutations results from the reaction of difunctional alcohols with diisocyanates to form polyurethanes (5,14). 

The reaction of isocyanates with alcohol is strongly exothermic. A portion of this heat can be removed and better quality control achieved by forming a prepolymer with half of the alcohol and the diisocyanate. The new prepolymer has isocyanate terminals and can be used with the remaining quantities of the difunctional and/or the trifunctional alcohol in the propellant mix. In recent years isocyanate-terminated polymers... 

The volatility of difunctional isocyanates (such as tolylene diisocyanates, hexamethylene diisocyanate, etc.) creates many environmental problems in the urethane industry. These difficulties can be overcome by preparation of NCO-terminated oligomers with low vapor pressure. One approach is the preparation of NCO-ter-minated oligomers by partial cyclotrimerization of difunctional isocyanates. Usually this is achieved by a multi-step process which includes also deactivation of the catalyst at a certain conversion. During our work on cyclotrimerization of isocyanates we found that cyclic sulfonium zwitterions are very active cyclotrimerization catalysts (2). Recently we found that cyclic sulfonium zwitterions under certain reaction conditions act as anionic initiators. This behavior of cyclic sulfonium zwitterions permits preparation of isocyanate oligomers containing isocyanurate rings by a one-step procedure, eliminating the deactivation step. 

Enamines of cyclic ketones may also be used to prepare polyamides in a different type of condensation reaction (67MI11100). This polymerization involves reaction with diisocyanates (Scheme 46), with the enamine functioning as a difunctional reagent. Morpholino- and piperidino-enamines are the most effective monomers. 

Dicarbodiimides have not gained the same prominence as diisocyanates as monomers for addition polymers. Dicarbodiimides are obtained from difunctional precursors, such as bis-thioureas. Another synthetic method is the conversion of diisocyanates with iminophosphoranes. The reaction can be condncted stepwise to give an isocyanato-carbodiimide as an intermediate. 

One of the first kinetic investigations of the reaction of diisocyanates with difunctional hydroxyl compounds was that of Bailey et al. [153]. Several diisocyanates were studied, using hydroxyl-terminated diethylene glycol adipate of 1800 molecular weight. Data obtained using 2,4-tolylene... 

The structural variations possible in R and R make it possible to vary the toughness and elasticity of the polyurethane adhesive. Polyesters or polyethers are prepared with terminal hydroxyl groups that can then be reacted with difunctional or polyfunctional isocyanates. Polyurethane prepolymers can be formed in Reaction 1, with the desired terminal group produced by using one or other of the diol and diisocyanate reactants in excess. 

The initial step in the production of cast elastomers is to terminate a low-molecular weight difunctional polyether or polyester by a mixture of toluene 2,4- and 2,6-diisocyanate using an excess of the diisocyanate (Eq. 21.20). 

Polyurethanes with a few chromophoric hard segment units which do not show phase separation can be obtained by a polyaddition reaction of only a macrodiol and a diisocyanate in nearly stochiometric amount (slight excess of diisocyanate) together with a small amount of a difunctional chromophore (DAAB), counterbalancing the diisocyanate excess. The structure of such polyurethanes investigated here are given in Fig. 13. 

Thermoplastic polyurethanes (TPU) are a versatile family of elastoplastic materials characterized by outstanding toughness and abrasion resistance. These materials are prepared from three principal reactants, a difunctional polyol, a difunctional chain extender and a diisocyanate in accordance with the following reaction ... 

Polycocyclotrimers were prepared by polycocyclotrimerization of difunctional isocyanates of variable chain length or difunctional isocyanate with monofunctional isocyanate. The stress-strain and viscoelastic properties of resulting polymers were determined. It was found that co-polycyclotrimers prepared from diisocyanates of the variable chain length had typical properties of phase separated block copolymers. 

If a trifunctional compound (triethanolamine) is reacted with a difunctional diisocyanate (for example TDI), in order to avoid undesired crosslinking, formation of big particles or high viscosities, the molar ratio between TDIrTEOA is usually less or equal to 1 1. For high solid content, lower TDIrTEOA ratios (around 0.6 1), are used. 

Polymer formation can occur through a variety of reactions. Metallocene polyamides, polyethers, polyesters, polyhydrazides and polyurethanes have been synthesized through condensation reactions of 1,1 -difunctional metallocenes (typically ferrocene derivatives) with diacid halides (if the metallocene derivative contains functional electron-pair donor bases) and electron-pair donor bases (as diamines, hydrazines, diisocyanates, diols) if the metallocene derivative contains functional electron-pair acceptor acids . 

Urethane-modified alkyds are similar to simple alkyds except that dibasic acid is replaced with a difunctional isocyanate such as toluene diisocyanate or hexamethylene diisocyanate. The process is also similar to simple alkyds. Coatings made with urethane-modified alkyds dry faster and harder than alkyds, yet retain flexibility. These systems have better water-, chemical- and abrasion-resistance than alkyd resins, and cost is also relatively low (Wicks et al., 1998). These are used in clear finishes for wood floors, cabinets, OEM, maintenance, and architectural coatings. The aliphatic-based systems are excellent for exterior use, or where UV exposure is possible, while aromatic-based systems usually have better abrasion-resistance. Chemo-enzymatic synthesis of urethane-based systems produces better control of stereochemistry and can impart unique properties (Athawale Bhabhe, 1998 Athawale Gaonkar, 1999 Athawale Joshi, 2000, 2004 Bhabhe Athawale, 1998). 

---