Polyurethan


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polyurethane

, polyurethan
a class of synthetic materials made by copolymerizing an isocyanate and a polyhydric alcohol and commonly used as a foam (polyurethane foam) for insulation and packing, as fibres and hard inert coatings, and in a flexible form (polyurethane rubber) for diaphragms and seals

Polyurethan

 

(or polyurethane), a polymer containing urethan groups, —NH—CO—O—, in the main chain of the macromolecule; the general formula for linear polyurethans is

[— A—OCOHN — A′ — NHCOO —]n

Polyurethans are usually produced by polycondensation of diisocyanates or polyisocyanates (A’ is a diisocyanate residue in the general formula) with compounds containing active hydrogen atoms, for example, dihydric and trihydric alcohols (A is a hydrocarbon residue). This process is often called polymerization or polycombination. The substances most commonly used in polyurethan synthesis include hexamethylene-l, 6-diisocya-nate, toluene-2,4- and 2,6-diisocyanates, tri(p-isocyanate phe-nyl)methane, aliphatic or aromatic polyethers and polyesters, glycols, and glycerol.

The properties of polyurethans vary over an extremely wide range, depending on the nature and length of chain segments between urethan groups and on the structure (linear or cross-linked), molecular weight, crystallinity and so on. Polyurethans may be viscous liquids or amorphous or crystalline solids, ranging from highly elastic soft rubbers to rigid plastics (Shore hardness from 15 on scale A to 60 on scale D, respectively). Polyurethans are resistant to acids, mineral and organic oils, gasoline and oxidizing agents; they surpass polyamides in resistance to hydrolysis. Linear polyurethans are soluble in certain polar solvents—for example, dimethylformamide and dimethyl sulfoxide.

Polyurethans are used as foams, rubbers, thermoplasts, fibers, varnishes, adhesives and latices for the preparation of potting compounds. Polyurethan articles are produced by direct liquid-phase molding from base monomers or from previously prepared polymers (prepolymers). World production of polyurethan was estimated at 1.2 million tons in 1973.

REFERENCES

Saunders, J. H., and K. C. Frisch. Khimiia poliuretanov. Moscow, 1968. (Translated from English.)
See also references under .

IU. L. MOROZOV

References in periodicals archive ?
Xu, "Polyurethanes having shape memory effects," Polymer, vol.
Stutz, "Surface Tension and Morphology in Blends of Thermoplastic Polyurethanes and Polyethylene," to be submitted to Polymer (1999).
To avoid this drawback, in this project high temperature resistant, aluminium filled Polyurethan casting resin systems are used as mould making material.
The recycling polyols thus produced have a set of fitting properties (hydroxyl number, viscosity, reactivity) for the proposed application and are converted to the desired polyurethanes by specially developed formulations, processed to coatings as the basic example in the laboratory with a Mathis LabDryer and characterized by physical measurements and mechanical tests.
The degradation of polyurethanes is a series of reaction steps based on the special properties of the reaction products contained in them.
The polyurethanes are synthesized from the recycling polyols according to Behrendt and Pohl[3].
The relaxation spectra of the polyurethanes made from the recycling polyols show some peculiarities compared to a typical polyurethane elastomer which are due to the composition of the polyols and the special procedure of their production.
Two examples show the characterization of the network structure by means of the dynamic-mechanical analysis: polyurethanes based on polyol P 15 or P 134, resp., the formulations and analytic data of which are given in Table 4.
The transition area at -21[degrees]C is caused by the onset of the segment mobility in the polyether elastic phase and marks in this way the first [alpha]-area of the phase-separated polyurethanes (for comparison: the transition areas of OH-functional high molecular weight polyether alcohols with an average molecular weight of ca.
Figure 7 shows the relaxation spectra of a series of polyurethanes produced from recycling polyols with increasing amount of soft polyurethane foam by the same solvolysis mixture of dipropylene glycol and di-n-butylamine (for composition, see Table 3).
The newly developed procedure of combined aminolysis and glycolysis of polyurethanes allows the production of recycling polyols with wide range properties which are useful for a great number of applications.
During the development of these polyols it became evident that the solvolysis procedure developed provides polyurethanes with elastic properties without any necessity of the addition of longchained primary raw materials.