Polyurethane crystallizing

Further nitration of the 2- and 4- isomers yields 2,4-dinitrotoluene, yellow crystals, m.p. 71 "C. This material is reduced to 2,4-di-aminotoluene and treated with phosgene to give 2,4-diisocyanatotoluene, a precursor of polyurethanes. 

A hst of polyol producers is shown in Table 6. Each producer has a varied line of PPO and EOPO copolymers for polyurethane use. Polyols are usually produced in a semibatch mode in stainless steel autoclaves using basic catalysis. Autoclaves in use range from one gallon (3.785 L) size in research faciUties to 20,000 gallon (75.7 m ) commercial vessels. In semibatch operation, starter and catalyst are charged to the reactor and the water formed is removed under vacuum. Sometimes an intermediate is made and stored because a 30—100 dilution of starter with PO would require an extraordinary reactor to provide adequate stirring. PO and/or EO are added continuously until the desired OH No. is reached the reaction is stopped and the catalyst is removed. A uniform addition rate and temperature profile is required to keep unsaturation the same from batch to batch. The KOH catalyst can be removed by absorbent treatment (140), extraction into water (141), neutralization and/or crystallization of the salt (142—147), and ion exchange (148—150). 

Mesogenic diols, such as 4,4 -bis( CO-hydtoxyaLkoxy)biphenyls, ate used with 2,4-TDI or 1,4-diisocyanatobenzene (PPDI) to constmct Hquid crystalline polyurethanes (7). Partial replacement of the mesogenic diols by PTMG shows that the use of lower molecular weight flexible spacers form polymers that have a more stable mesophase and exhibit higher crystallinity (8). Another approach to Hquid crystal polyurethanes involves the attachment of cholesterol to the polyurethane chain utilizing the dual reactivity in 2,4-TDI (9). 

Crystalline polyesters are highly important as adhesive raw materials. They are normally crystalline waxes and are highly symmetrical in nature, which can aid the crystallization process [26]. Poly(hexamethylene adipate) and poly(caprolactone), shown in Table 2, are only two of the many crystallizable backbones. Poly(ethylene adipate) and poly(letramethylene adipate) are also commonly used in urethane adhesives. The crystalline polyesters are used in curing hot melts, waterborne polyurethanes, thermoplastic polyurethanes, and solvent-borne urethane adhesives. The adipates are available mostly as diols. The poly(caprolactones) are available as diols and triols. 

The thermoplastic polyurethane (TPU) adhesives must, of necessity, contain low gel content because they must be processable in an extruder. Most adhesives are relatively linear, with a functionality of 2.0, although small amounts of branching may be introduced, usually at the expense of a lower melt flow. Good physical properties of TPU s are obtained when the thermoplastic urethanes have molecular weights of 100,000 or higher (see p. 56 in [63]). Most TPU adhesives are based on symmetrical polyesters with a fast crystallizing backbone or a backbone slightly modified to increase the open time. 

Aortal Aery Me ABS Alkyd Alloy /Blands Barrier Resin CeliAwie Diallyl Phthalates Engineering Plastics Epoxies Fluorepdlymars Liquid Crystal Melamine Nitrile Resins Nylon Phenolic Polyamlde-lmide Polycarbonate polyester Polyethylene Polyimictes Polypropylene Polyurethanes PVC... 

T.L. Boggs et al, AIAA J 8 (2), 370-72 (1970) CA 72, 113371 (1970) Scanning electron microscopy is used to study the surface structure of solid proplnts, prepd from AP (1) and polyurethane or caiboxylated polybutadiene. Polyurethane proplnts are self-extinguish-ing at high pressure due to the flow of molten binder over I crystals. I crystals formed a thin surface melt with gas liberation in the molten phase... 

Linear polyurethanes, 26 Linear step-growth polymerizations, 13 Lipase-catalyzed polyesterifications, 83 Lipases, 82, 84 catalytic site of, 84 Liquefied MDIs, 211, 226-227 Liquid carbon dioxide, 206 Liquid-castable systems, 201 Liquid crystal devices (LCDs), alignment coating for, 269-270 Liquid crystalline aromatic polyesters, 35 Liquid crystalline polyesters, 25, 26, 48-53... 

Alternating copolymers, as illustrated in Fig. 5.8 b), are generally made by condensation polymerization of two different monomers. Such copolymers display regularity and are capable of crystallizing under the appropriate conditions. Examples of such copolymers include nylons 66 and 610, and various types of polyurethane. 

Polyolefin foams are easier to model than polyurethane (PU) foams, since the polymer mechanical properties does not change with foam density. An increase in water content decreases the density of PU foams, but increases the hard block content of the PU, hence increasing its Young s modulus. However, the microstructure of semi-crystalline PE and PP in foams is not spherulitic, as in bulk mouldings. Rodriguez-Perez and co-workers (20) showed that the cell faces in PE foams contain oriented crystals. Consequently, their properties are anisotropic. Mechanical data for PE or PP injection mouldings should not be used for modelling foam properties. Ideally the mechanical properties of the PE/PP in the cell faces should be measured. However, as such data is not available, it is possible to use data for blown PE film, since this is also biaxially stretched, and the texture of the crystalline orientation is known to be similar to that in foam faces. 

McKeiman RL, Heintz AM, Hsu SL, Atkins EDT, Penelle J, Gido SP. Influence of hydrogen bonding on the crystallization behavior of semicrystalline polyurethanes. Macromolecules 2002 35 6970-6974. 

Figure 14. Cavity formation around NH lClOh crystals in polyurethane...

In unfilled rubbers, which are not capable of strain-induced crystallization, the upturns on Mooney-Rivlin curves have shown to be absent 92 95). They disappear also in crystallizable rubbers at elevated temperatures and in the presence of solvents. On the other hand, the upturns do not appear for butadiene, nitrile and polyurethane rubbers if the limited chain extensibility function is introduced in the Mooney-Rivlin expression 97). Mark 92) has concluded that in the absence of selfreinforcement due to strain-induced crystallization or domains the rupture of the networks occurs long before the limited chain extensibility can be reached. 

URETHANE. [CAS 51-79-6], CO(NH2)OC2H5, also referred to as ethyl carbamate or ethyl urethane. Its structure is typical of the repeating unit in polyurethane resins. Colorless crystals or white powder, odorless, saltpeterlike taste. D 0.9862. mp 49C, bp 180C solutions neutral to litmus, soluble in w ater, alcohol, ether, glycerol, and chloroform slightly soluble in olive oil. Formed by the heating of ethanol and urea nitrate to 120-130% or by the action of ammonia on ehtyl carbonate or ethyl chloroformate. 

The formation of cellular products also requires surfactants to facilitate the formation of small bubbles necessary for a fine cel] structure. The most effective surfactants are polyoxyalkylene-polysiloxane copolymers. The physical properties of polyurethanes are derived from their molecular structure and determined by the choice of building blocks as well as the suprainolecular structures caused by atomic interaction between chains. The ability to crystallize, the flexibility of the chains, and spacing of polar groups are of considerable importance, especially in linear thermoplastic materials. In rigid cross-linked systems, e.g., polyurethane foains, other factors such as density determine the final properties. 

The addition of small amounts (ca 0,6%) of cellulose esters removes exudate by absorption, and also reduces the tendency to crack (Ref 17) polyurethanes remove exudate and double the compressive strength of the case (Ref 8), or impart finer crystal structure to the TNT matrix (Ref 33). Exudation is also, discussed in a limited-access report (Ref 11)... 

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