Monomer in synthesis of polyurethanes

Phosgene is a key intermediate used in synthesis of many chemicals, a major one being toluene diisocyanate, a monomer in polyurethanes. Phosgene is made from chlorine and carbon monoxide through the overall reaction... 

Step-growth polymerization, 22, 24-25, 23, 84-86, 86,90-92,114-115, 261 compared with chain-growth polymerization, 88-89, 88-89 interfacial polymerization, 91-92 laboratory activities on synthesis of nylon, 228-230 synthesis of polyesters in the melt, 231-233 synthesis of polyurethane foam, 234-237 molar mass and, 86, 86 polycondensation of poly ethylene terephthalate), 90-91 polymers produced by, 86 types of monomers for, 90 Stereochemistry, 28, 37-39,41-42, 70 tacticity, 103-105 Stereoisomers, 41 Stereoregularity, 70 Stiffness, 142, 261 Strain, 142-143, 261 Strength... 

As mentioned previously, the synthesis of polyurethanes, by the reaction of a diisocyanate (or polyisocyanate) with oligo-diols (or oligo-polyols), is a polyaddition reaction (or step-addition polymerisation), a particular type of polycondensation reaction. There is a great difference between the polycondensation and the polyaddition reactions and the classical radical polymerisation or ionic (living) polymerisation reactions. In radical polymerisations (typical chain reactions), the high MW polymer is formed at the beginning of polymerisation. The reaction system is constituted from monomer and high... 

In spite of polyurethane is a hazardous polymer, it can be modified through the basic chemistry of polyurethanes, which can modify a wide variety of soft and hard segments, morphological features, thermic and mechanical properties of structures, just by changing several conditions, such as the ratio NCO/OH, the aliphatic or aromatic isocyanate, the molecular weight, and the ester or ether form of the polyol, but especially the nature of the monomer, whether synthetic or natural. Among the natural options than can be used for synthesis are oil, polysaccharides, and amino acids. 

A synthesis and characterization of an active styrylthiophene monomer and formation of polyurethane with second-order optieal nonlinearity was reported by Wang et al. This was carried out on (trans)-7-[4-N,N-(dihydroxyethyl)aminobenzene-ethenyl-3,5-dinitrothiophene to form the corresponding prepolymer, polyurethane.. The prepolymer and polyurethane are claimed to exhibit good thermal stability and good solubility, in eommon organie solvents. The dss coefficient of the dieleetrie polarized films was reported, to be 40.3 pmW. 

When the arenediamines 2,4,6-trimethylbenzene-l,3-diamine and 2,2, 6,6 -tetramethyl-4,4 -methylenediphenylamine were treated under the same reaction conditions with 1.4 equivalents of B0C2O and 1.0 equivalent of DMAP per amino group in acetonitrile at room temperature Method A, work-up with sulfuric acid), 2,4,6-tnmethylbenzene-l,3-diisocyanate 339 and 2,2, 6,6 -tetramethyl-4,4 -meth-ylenediphenyl isocyanate 340 were obtained in yields of 84% and 93%, respectively. Arenediyl diisocyanates play a very important role as monomers for the industrial synthesis of polyurethanes and polyureas [226]. 

The use of HMF or the corresponding dialdehyde precursors obviously applies to the synthesis of monomers for polycondensation reactions as shown by the examples given in Scheme 2. ITiese difimctional structures again mimic the corresponding well-known aliphatic and aromatic counterparts used in the preparation of polyesters, polyamides, polyurethanes, etc. 

We will return to these reactions later in connection with polyurethanes because one monomer in polyurethanes is toluene diisocyanate, and the first step in its synthesis is the production of dinitrotoluene. 

During synthesis of a polymer, particularly of polyurethane, gaseous products can appear. Therefore, a complete model of the process must take into account (at least in some cases) the possibility of local evaporation and condensation of a solvent or other low-molecular-weight products. Such a complex model is discussed for chemical processing of polyurethane that results in formation of integral foams in a stationary mold.50 In essence, the model is an analysis of the effects of temperature in a closed cell containing a solvent and a monomer. An increase in temperature leads to an increase in pressure which influences the boiling temperature of the solvent and results in an increase in cell volume. The kinetics of polymerization is described by a simple second-order equation. The... 

Polymerization of epoxy monomers, requiring probably the simultaneous participation of the phenolic hydroxy group, and the production of polyurethanes are the main applications of the abovementioned catalysts. In particular, their role in the trimerization of the i.scx yanate group " appears quite relevant and several investigations of the synthesis of epoxy resins-- " - and polyurethanes- arc reported. A different type of catalyst is constituted by acetophenone-derived p-aminoketones employed with photocurable resins. -- ... 

It is very clear that only the first group of monomers, which lead to termination by recombination, can be used for synthesis of hydroxy-telechelic polymers which are useful in polyurethane fabrication and from the second group of monomers it is impossible to obtain oligo-polyols useful in PU. 

With the development of polymer science and the synthesis of new polymers, the previous definition of condensation polymer is inadequate. For example, in polyurethanes (Table 1.2), which are classified as condensation polymers, the repeating unit has the same net composition as the two monomers (i.e., a diol and a diisocyanate), which react without eliminating any small molecule. To overcome such problems, chemists have introduced a definition which describes condensation polymers as consisting of structural units joined by internal functional groups... 

In the 1980s, the successful synthesis of elastomeric polyamides 120 of high molecular weight (d/n =10,000-18,000) was reported from the polycondensation of l,l -bis(/ -aminoethyl)ferrocene with diacid chlorides (Scheme 13). Also, polyureas 121 were prepared from the same ferrocene monomer and diisocyanates, and polyesters and polyurethanes were prepared from l,l -bis(/ -hydroxyethyl)ferrocene. However, the latter materials had much lower molecular weights and were characterized only by scanning electron microscopy. X-ray, and IR analyses. The introduction of ferrocenes in which the functional groups are separated from the cyclopentadienyl ring by at least two methylene units was crucial in order to reduce steric effects and to avoid the instability found previously in polymers of a-functionalized ferrocene due to the a-ferrocenyl carbonium ion stability. 

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