Diisocyanate component

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. 

The effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase were examined (Figure 8). The rates of hydrolysis of the polyurethanes containing MDI or tolylene-2,U-diisocyanate (TDI) were smaller than that of the polyurethane containing 1,6-hexamethylene-diisocyanate (HDI). 

Figure 8. Effects of chemical structure of diisocyanate component on the hydrolysis of polyurethanes by R. delemar lipase.

Soft Segments. The soft segments are the linear reaction products of the diisocyanate component, e.g., MDI (diphenylmethane-p,p -diiso-cyanate), and the macroglycol component, e.g., PTAd [poly (tetramethyl-ene adipate) glycol], as is seen in Figure 3. 

Hard Segments. The hard segments are the linear reaction products of the diisocyanate component and the third monomer type in the TPU elastomer recipe, the small glycol-chain-extender component. In Figure 5 we see a typical TPU hard-segment structure which is formed from MDI and 1,4-BDO (1,4-butanediol). 

Several types of diisocyanates (aromatic, aliphatic, cyclo aliphatic) and many different glycol-chain extenders (open-chain aliphatic, cyclo aliphatic, aromatic aliphatic) can be used to produce TPU-elastomer hard segments. In the more conventional and practical formulations only a single diisocyanate component is used to make a TPU, so the diisocyanate is common to both the hard and soft segments. The polymer chemist makes his diisocyanate and glycol-chain-extender component selections based on such considerations as desired TPU mechanical properties, upper service temperature, environmental resistance, solubility characteristics, and economics. 

Hard- and Soft-Segment Polymers. The structure of the diisocyanate component has a significant influence on dynamic mechanical properties of both hard- and soft-segment polymers. Both 2,4- and 2,6-TDI/ BD a relaxations occur at about the same temperature and have a comparable activation energy. However, the symmetrical structure of... 

Pyrolysis could be considered as an nnsnitable way of recycling for polyurethanes because the liquid product is extremely viscous and can solidify over time [41]. The main reason of the severe instability of polynrethane pyrolysate is the reactivity of the diisocyanate component, the regained polynrethane-forming reactant. The other component of thermoplastic polyurethanes is either a polyether or a polyester which could lead to stable pyrolysis liquid if the reactive diisocyanate is eliminated from it. 

Linear aliphatic fluorinated polyurethanes have been tested with respect to the location of the fluorine atoms in the diol or diisocyanate component. Fluorine atoms introduced into the diisocyanate unit increase the stability of the urethane group, but the presence of these atoms in the diol unit favours dissociation of the urethane group to monomer. Comparison of PTFE and perfluoroamidine polymers shows that introduction of triazine rings in fluoromethylene chains enhances their stability. 

Certain fibers and non-wovens are made commercially by the isocyanate route, such as P84. For this family, 4,4 -BTDA and PMDA are used as dianhydride components, and toluene diisocyanate and diisocyan-atodiphenyl methane are used as diisocyanate components. ... 

A representative example is the synthesis of amino acid based polyurethanes using L-tyrosine based chain extender, PEG and polycaprolactone diol as soft segments, and HDI and HMDI as diisocyanate components [38, 39]. By altering the soft and diisocyanate components, the researchers were able to prepare a number of polyurethanes with varying hydrophobicities and degradation behavior. 

To introduce functional groups, polymer blends were produced in the extruder from PCU and poly(vinyl alcohol) (PVA) with 10, 20 and 30 mass% PVA. In addition, the commercial products Mitrathane and Tecoflex were applied as carrier materials. While Mitrathane is built up of the aromatic diisocyanate MDI, hydroxytelechelic polytetrahydrofuran and an aliphatic amine as chain prolonger, Tecoflex consists of a cycloaliphatic diisocyanate component (Table 2). The... 

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