Polyurethane formation

Step polyaddition (urethane formation) Polyurethanes with large M can be prepared using a method based on the Wnrtz alcohol test. In the presence of a basic catalyst such as a diamine, ionic addition takes place, for example, between 1,4-butanediol and 1,6-hexanediisocyanate ... 

As with polyesters, the amidation reaction of acid chlorides may be carried out in solution because of the enhanced reactivity of acid chlorides compared with carboxylic acids. A technique known as interfacial polymerization has been employed for the formation of polyamides and other step-growth polymers, including polyesters, polyurethanes, and polycarbonates. In this method the polymerization is carried out at the interface between two immiscible solutions, one of which contains one of the dissolved reactants, while the second monomer is dissolved in the other. Figure 5.7 shows a polyamide film forming at the interface between an aqueous solution of a diamine layered on a solution of a diacid chloride in an organic solvent. In this form interfacial polymerization is part of the standard repertoire of chemical demonstrations. It is sometimes called the nylon rope trick because of the filament of nylon produced by withdrawing the collapsed film. 

Mixtures of HNO, H2SO4, and SO also result in high concentrations of NO/, and toluene can be readily nitrated at —40 to — 10°C as a result (6). At these low temperatures, the formation of the meta-isomer of mononitrotoluene (MNT) is greatiy reduced. Such a reduction is highly desired in the production both of dinitrotoluenes (DNTs) employed to produce intermediates for polyurethane production and of trinitrotoluene (TNT), which is a high explosive. > -MNT results in the production of undesired DNT and TNT isomers (see Nitrobenzene and nitrotoluenes). 

Phosphoms compounds are effective flame retardants for oxygenated synthetic polymers such as polyurethanes and polyesters. Aryl phosphates and chloroalkyl phosphates are commonly used, although other compounds such as phosphonates are also effective. The phosphoms compounds can promote char formation, thereby inhibiting further ignition and providing an efficient thermal insulation to the underlying polymer. 

Step-growth polymerization is characterized by the fact that chains always maintain their terminal reactivity and continue to react together to form longer chains as the reaction proceeds, ie, a -mer + -mer — (a + )-mer. Because there are reactions that foUow this mechanism but do not produce a molecule of condensation, eg, the formation of polyurethanes from diols and diisocyanates (eq. 6), the terms step-growth and polycondensation are not exactly synonymous (6,18,19). 

Almost all IDA derived chain extenders are made through ortho-alkylation. Diethyltoluenediamine (DE I DA) (C H gN2) (53), with a market of about 33,000 t, is the most common. Many uses for /-B I DA have been cited (1,12). Both DE I DA and /-B I DA are especially useful in RIM appHcations (49,53—55). Di(methylthio)-TDA, made by dithioalkylation of TDA, is used in cast urethanes and with other TDI prepolymers (56). Styrenic alkylation products of TDA are said to be useful, eg, as in the formation of novel polyurethane—polyurea polymers (57,58). Progress in understanding aromatic diamine stmcture—activity relationships for polyurethane chain extenders should allow progress in developing new materials (59). Chlorinated IDA is used in polyurethane—polyurea polymers of low hysteresis (48) and in reinforced polyurethane tires (60). The chloro-TDA is made by hydrolysis of chloro-TDI, derived from TDA (61). 

Urethane network polymers are also formed by trimerization of part of the isocyanate groups. This approach is used in the formation of rigid polyurethane-modified isocyanurate (PUIR) foams (3). 

Polyurethane Formation. The key to the manufacture of polyurethanes is the unique reactivity of the heterocumulene groups in diisocyanates toward nucleophilic additions. The polarization of the isocyanate group enhances the addition across the carbon—nitrogen double bond, which allows rapid formation of addition polymers from diisocyanates and macroglycols. 

Hyperbranched polyurethanes are constmcted using phenol-blocked trifunctional monomers in combination with 4-methylbenzyl alcohol for end capping (11). Polyurethane interpenetrating polymer networks (IPNs) are mixtures of two cross-linked polymer networks, prepared by latex blending, sequential polymerization, or simultaneous polymerization. IPNs have improved mechanical properties, as weU as thermal stabiHties, compared to the single cross-linked polymers. In pseudo-IPNs, only one of the involved polymers is cross-linked. Numerous polymers are involved in the formation of polyurethane-derived IPNs (12). 

The formation of isocyanurates in the presence of polyols occurs via intermediate aHophanate formation, ie, the urethane group acts as a cocatalyst in the trimerization reaction. By combining cyclotrimerization with polyurethane formation, processibiUty is improved, and the friabiUty of the derived... 

Water-borne polyurethane coatings are formulated by incorporating ionic groups into the polymer backbone. These ionomers are dispersed in water through neutrali2ation. The experimental 1,12-dodecane diisocyanate (C12DI Du Pont) is especially well suited for the formation of water-borne polyurethanes because of its hydrophobicity (39). Cationomers are formed from IPDI, /V-methyIdiethan olamine, and poly(tetramethylene adipate diol)... 

Metal salts of neodecanoic acid have also been used as catalysts in the preparation of polymers. For example, bismuth, calcium, barium, and 2kconium neodecanoates have been used as catalysts in the formation of polyurethane elastomers (91,92). Magnesium neodecanoate [57453-97-1] is one component of a catalyst system for the preparation of polyolefins (93) vanadium, cobalt, copper, or kon neodecanoates have been used as curing catalysts for conjugated-diene butyl elastomers (94). 

The formation of more replaced compounds in studied conditions is not have place. Maximal yield on surface polyurethane foam of salts is observed by pH 2-6. By pH<2 the equilibrium ionic exchanges was displaced left and by pH<0,5 the sorbent practical completely was regenerated. It was studied the influence of the weight of sorbent, the nature of cations of light alkali and alkali earth metals and any other factors on the coefficient concentration ofM(I). 

Isocyanates are highly reactive materials and enter into a number of reactions with groups containing active hydrogen. The reactions of most important in the formation of polyurethanes are ... 

Another area of recent interest is covulcanization in block copolymers, thermoplastic rubbers, and elasto-plastic blends by developing an interpenetrating network (IPN). A classical example for IPN formation is in polyurethane elastomer blended acrylic copolymers [7]. 

Step-growth polymerization processes must be carefully designed in order to avoid reaction conditions that promote deleterious side reactions that may result in the loss of monomer functionality or the volatilization of monomers. For example, initial transesterification between DMT and EG is conducted in the presence of Lewis acid catalysts at temperatures (200°C) that do not result in the premature volatilization of EG (neat EG boiling point 197°C). In addition, polyurethane formation requires the absence of protic impurities such as water to avoid the premature formation of carbamic acids followed by decarboxylation and formation of the reactive amine.50 Thus, reaction conditions must be carefully chosen to avoid undesirable consumption of the functional groups, and 1 1 stoichiometry must be maintained throughout the polymerization process. 

Although the name polyurethane might be taken as implying that these materials contain urethane groups (—NHCOO—) in the backbone of the macromolecule, for those polyurethanes in major commercial use this is not tme. For such materials the initial macromolecule tends to be a polyester or polyether it is the crosslinks that involve the formation of a polyurethane stmcture. 

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