Diisocyanate Double bond

Polyurethane Formation. The key to the manufacture of polyurethanes is the unique reactivity of the heterocumulene groups in diisocyanates toward nucleophilic additions. The polarization of the isocyanate group enhances the addition across the carbon—nitrogen double bond, which allows rapid formation of addition polymers from diisocyanates and macroglycols. 

The first type includes vulcanising agents, such as sulphur, selenium and sulphur monochloride, for diene rubbers formaldehyde for phenolics diisocyanates for reaction with hydrogen atoms in polyesters and polyethers and polyamines in fluoroelastomers and epoxide resins. Perhaps the most well-known cross-linking initiators are peroxides, which initiate a double-bond... 

Synthesis of a Urethane Vinyl Ether Oligomer. A urethane vinyl ether oligomer was prepared by the procedure discussed by Lapin.15 Reacting a hydroxyalkyl vinyl ether, an oligomeric diol and a diisocyanate gave and oligomer that had a Brookfield viscosity of 3.7 million mPa-s and a theoretical equivalent weight of 1000 g per vinyl ether double bond. 

The reactive oligomer can be any low-molar-mass polymer containing at least a couple of double bonds. It can be based on a polyester, polyether, or polyurethane backbone. One mole of a, oo-OH-terminated polyester or polyether is prereacted with two moles of acrylic acid to obtain an a, oo-diacrylate oligomer. For polyurethanes, 1 mole of a, m-diisocyanate oligomer is prereacted with 2 moles of hydroxyethylacrylate (Sec. 2.2.3c). 

In addition, Eq. (5.1) should not be applied in systems that exhibit different initial reactivities of functional groups, such as in the copolymerization of double bonds of a particular unsaturated polyester with styrene or in the formation of a polyurethane starting from 2,4-toluene diisocyanate. 

The reactivity of unsaturations with ozone has been applied to produce structures which allow subsequent degradation of materials by ozonolysis. In this way, Peters et al. [105] prepared polyurethanes using novel unsaturated diisocyanates which can be degraded by oxidative cleavage of the double bonds. 

Because of their much higher costs, aliphatic diisocyanates find use mainly in specialized areas where their special properties such as nonyellowing in light are of great importance. The nonyellowing is a result of the aliphatic structure of the isocyanate. There are no series of double bonds that cause the yellowing. 

Polyurethanes are important synthetic macromolecules. They are manufactured, for example, in the form of foams. Such a foam is obtained during the formation and solidification of the polyurethane when a gas escapes from the reaction mixture, expanding the material. An elegant possibility for generating such a gas uniformly distributed everywhere in the reaction medium is as follows besides the diol, one adds a small amount of H20 to the diisocyanate. H20 also adds to the C=N double bond of the diisocyanate. According to the uncatalyzed addition mechanism of Figure 8.12, this produces an A-arylated free carbamic acid Ar—NH— C(=0)—OH. However, such a compound decomposes easily in perfect analogy to the decom-... 

Poly(iminoborane)s [(-BR=N-)n] are a potential 7t-conjugated polymers, since boron-nitrogen bonds possess the double bond like nature owing to pTt-pjt interaction However, these materials are not fully characterized so far 10>. In order to incorporate the monomeric B-N bond into the conjugation path, we examined an alternating boration copolymerization between diisocyanates and diynes making use of different reactivity between haloboration and phenylboration reactions. 

The resulting unsaturated diols (practically monoglycerides of fatty acids, reaction 17.12) react with diisocyanates (for example with toluene diisocyanate) at around 80-90 °C, usually in a solvent such as toluene, xylene or naphtha. Unsaturated PU are obtained, which are crosslinked by a radical mechanism with the transformation of the multiple double bond in a crosslinked network (Figure 17.9). This reaction is used for the fabrication of urethane alkyd coatings. Other polyols may be used instead of glycerol ethylene glycol, neopentylglycol, trimethylolpropane, pentaerythritol and others. 

Carbonyl diisocyanate (46) was shown to undergo a Diels-Alder type of cycloaddition with azomethines to give 2,3,6,7-tetrahydro-4/7,8/7-[l,3,5]triazino[2,l-Z>][l,3,5]oxadiazin-4,8-diones (16) (Scheme 5). A large variety of the triazino[2,l-ft][l,3,5]oxadiazines were realized by the suitable selection of dienophiles. Thus, l,3,5-triazino[2,l-Z>][l,3,5]oxadiazines (17), (18 R = NMe), and (19) and were synthesized by the reaction of carbonyl diisocyanate with alkyl or aryl isocyanates, dimethyl cyanamide, or aliphatic carbodiimides, respectively <86CB1133>. Due to the high reactivity of the cumulated double bonds, carbonyl diisocyanate (46) was also found to undergo [4 + 2] cycloadditions with cyclohexanone to yield cyclohexan-l-spiro-9 -[l,3,5]-oxadiazino-[3,4-e][l,3,5j-dioxazin-5 -spiro-l"-cyclohexane-2, 7 -dione (47) (Scheme 6) <76LA1634>. 

Isocyanates include the group -NCO in which both the oxygen and the nitrogen are bound to the carbon with a double bond. They include ethyl isocyanate and toluene diisocyanate which are both characteristically toxic and flammable. Often toxic, isocyanates react with water to form carbon dioxide. 

Note The definition ignores loss of double bonds. The Carothers definition fails to describe all the polymers that can fit into the category of condensation polymers, yet form without an evolution of a byproduct. An example is a polyurethane that can form from a reaction of a glycol with a diisocyanate ... 

Monoglycerides and partial glycerides obtained by alcoholysis are reacted with diisocyanates to synthesise polyurethanes (Fig. 6.8). Polyurethanes containing vinyl double bonds are prepared by treating partial glycerides (mono and di) obtained from linseed oil with methyl vinyl isocyanate... 

On this basis, it is not surprising that only a few kinds of reaction have so far been successfully applied in the synthesis of high-molecular linear polycondensates. High-molecular-weight polyesters (Section 26.4) or polyamides (Section 28.3) are obtained both by direct esterification or direct amidation of acids and by fr ns-esterification or Schotten-Baumann type reactions (see Section 17.4). The synthesis of polyurethane from diisocyanates and diols represents an addition of H to the N= double bonds (Section 28.5). Other addition reactions, such as HS—R—SH -h CH2=CH—R —CH=CH2 HS—R—S—CH2—CH2—R —CH=CH2, have not achieved any commercial significance. Poly(alkylene sulfides), on the other hand, are produced by nucleophilic substitutions (Section 27.1), while the polycondensation of benzyl chloride is an electrophilic substitution ... 

To prepare polymer wood, wood is degassed and then loaded with a suitable monomer. The monomer is then polymerized. For polycondensations, the preferred monomers are those that do not eliminate volatile components during polymerization (diisocyanates). Both ring-containing monomers (epoxides) and monomers with carbon-carbon double bonds can be polymerized. In the case of the latter, polymerization can be initiated by y-irradiation, peroxides, redox systems, etc. Not all monomers are suitable for the manufacture of polymer wood. Poly(acrylonitrile), for example, is insoluble in its own monomer. In wood, therefore, the precipitation polymerization leads to powdery deposits and not to a continuous phase. The same problem occurs with vinyl chloride, and in this case the boiling point of the monomer (—14 C) is too low. Poly(vinyl acetate) has too low a glass-transition temperature. In addition, monomers with low G values (see Section 21.2.1) need high doses of y rays to initiate polymerization. Commercially used polymers include, e.g., copolymers of styrene and acrylonitrile, poly(methyl methacrylate), and unsaturated polyesters. 

Cross-link sites are urethane active hydrogen atoms, active methylene groups (e.g., from the use of a diisocyanate such as methylenebis(4-phenylisocyanate), or allylic hydrogen atoms from double bonds incorporated into for vulcanization by sulfur. 

Isophorone diisocyanate (IPDI) n. An isocyanate used in the production of urethane elastomers and foams. It is less volatile than toluene diisocyanate, therefore easier to maintain at low levels in workers airspace and safer to work with. Its structure is modified from that of isophorone, above, in that the oxygen has been replaced by an -N=C=0 group, the double bond is gone, and the top carbon atom in the ring has an additional -CH2N=C=0 linked to it. 

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