Diphenylmethane diisocyanate structure

A similar structure to the one in Figure 6.6 is obtained by using instead of epoxy resins diphenylmethane diisocyanate (MDI pure or crude ). For example by using crude MDI with the functionality of around 2.2-2.5 -NCO groups/mol, by the reaction with terminal groups of high molecular weight polyether triols (5000-6500 daltons), nonreactive NAD... 

Materials. 4-[(2-Hydroxyethyl)amino]-2-(hydroxymethyl)-4 -nitroazobenzene (T-AZODIOL) (10) was used as the NLO chromophore whose dipole moment is aligned transverse to the main chain. T-AZODIOL was synthesized via two step reactions as shown in Schemes 1 and 2. As shown, 3-(2-hydroxylamino)-benzylalcohol (DIOL) prepared from w-aminobenzyl alcohol with 2-chloroethanol was coupled with diazotized / -nitroaniline to give rise to T-AZODIOL. The details of the synthetic procedures were previously reported (8). 4-[N-(2-Hydroxyethyl)-N-methylamino]-3 -(hydroxymethyl)-azobenzene (AZODIOL) dye was the NLO chromophore monomer for preparing the polymer with NLO chromophore incorporated in the main chain. Detailed synthetic procedures of AZODIOL were previously reported (5), Commercially available 2,4-tolylene diisocyanate (TDI) and 4,4 -diphenylmethane diisocyanate (PDI) were used without further purification. The chemical structures of these monomers are shown in Figure 1. 

A structure study was carried out on a model compound of one elastomer prepared with 4,4 -diphenylmethane diisocyanate and butanediol hard segments. It was shown that the chains are... 

A structure study was carried out on a model compound of one elastomer [ 130] prepared with 4,4 -diphenylmethane diisocyanate and butanediol hard segments. It was shown that the chains are probably linked together in stacks through C=0 - H-N hydrogen bmids between the methane groups. This bonding stabilizes the overall structure in both directions, perpendicular to the chain axis. Such an arrangement of the molecules was also proposed earlier [131]. 

This leads to the appearance of both anti and syn rotational conformations, which coexist in the DBDI based PU macromolecules, (Fig. 2.4-2.6). As a result, in this latter case the PU macromolecules can adopt a more compact packing which enhances significantly the ability to order in crystalline structures involving predominantly the anti form [60]. Shown in Fig. 2.4 and 2.5 are the extended linear anti and contorted syn DBDI positions as compared to the conventional rigid 4,4-diphenylmethane diisocyanate (MDI) non-crystallizing (Fig. 2.6). 

As polyurethane intermediates react rapidly and stoichiometrically with each other, a system of nomenclature is widely used to describe the structure of individual block copolymers. Suppose, for example, a typical polyurethane consisted of polycaprolactone,4,4 -diphenylmethane diisocyanate, and 1,4-butane diol, present in the molar ratio 1 3 2, then such a polymer is reported as a 1 3 2 block copolymer and this represents a simple, convenient and rapid method of identifying the basic urethane polymer structure. The ratio of each component in the block copolymer has a dramatic effect on its properties, as shown by the data in Table 2.2. 

Lithium and sodium salts have been complexed with propylene oxide/ethylene oxide block copolymers. Conductivity was markedly increased in the complexes over that of the polymers, with the greatest increases occurring at low salt concentrations where the salt is mainly increasing Tg (175). Another study conducted in nonaqueous solution indicated that conductivity in the block copolymer complex, as well as in other complexes, was affected by the size of the metal cation and the nature of the solvent in which the complex was formed, as well as by polymer composition and structure (176). A block copolymer prepared by coupling ethylenediamine and poly(ethylene glycol) with 4,4 -diphenylmethane diisocyanate and doped with lithium perchlorate yielded high ionic conductivity (177). 

Dozens of isocyanate functional compounds have been synthesized, but only a few find much use in urethane structural adhesives. The choices are largely dictated by a combination of performance, price, and safety considerations. Most of the materials used in adhesives are derived from the aromatic isocyanates, toluene diisocyanate (TDI) and diphenylmethane diisocyanate (MDI). 

Below, we first consider the shape memory effect, as well as basic structure-property relationships of TPU having crystalline soft segments, e.g., poly(tetra-methylene adipate) glycol (PTAd, M = 2000), and hard segments composed of 4,4 -diphenylmethane diisocyanate (MDI) and ethylene glycol (EG) or ethylene diamine (EDA) [25],... 

Based on the above studies, the identity of the diisocyanate component in BPUla was deduced by the presence of fragments at ra/z 250 [methylene-bis(4)phenyl-isocyanate] (MDI), 224 (4-amino-4 -iso-cyanato-diphenylmethane), and 198(diamino-diphenylmethane).27 The presence of the diamine, as the chain extender was evident from the presence of the fragments m/z 324, assignable to 1,l -bisCB-iso-jg cyanatoethyl)ferrocene, and 298, assignable to the structure 10. 

Reactivities of isocyanates depend on their structure. Table 2.6 gives the main isocyanates used for polymer network synthesis. Conjugation with aromatic nuclei makes ArNCO particularly reactive. The reactivity of diisocyanates is well documented in the literature. For symmetric diisocyanates such as diphenylmethane 4,4 -diisocyanate (MDI) or para-phenylene 4,4 -diisocyanate (PPDI), both NCO groups have initially the same reactivity. But as the NCO group itself exhibits an activating effect on isocyanate reactivity, the fact that one NCO group has reacted introduces a substitution effect that usually decreases the reactivity of the second NCO group. 

Thermal degradation of foams is not different from that of the solid polymer, except in that the foam structure imparts superior thermal insulation properties, so that the decomposition of the foam will be slower than that of the solid polymer. Almost every plastic can be produced with a foam structure, but only a few are commercially significant. Of these flexible and rigid polyurethane (PU) foams, those which have urethane links in the polymer chain are the most important. The thermal decomposition products of PU will depend on its composition that can be chemically complex due to the wide range of starting materials and combinations, which can be used to produce them and their required properties. Basically, these involve the reaction between isocyanates, such as toluene 2,4- and 2,6-diisocyanate (TDI) or diphenylmethane 4,3-diisocyanate (MDI), and polyols. If the requirement is for greater heat stability and reduced brittleness, then MDI is favored over TDI. 

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