Aniline-formaldehyde polymers

Rastogi and Bisht (Ref 3a) made combustion studies on hybrid propints consisting of o-s m-and p-toluidine nitTates with aniline-formaldehyde polymer as solid fuels, and red fuming nitric acid as oxidizer. They found that the results fitted a burning rate equation of the type, = a (G)v, where a and v are constants and G is the mass velocity. The authors conclude that the heterogeneous combustion reaction is diffusion controlled, and its rate is dependent on particle size... 

For the purposes of this chapter, aminopolymers are defined as polymers formed by the interaction of amines or amides with aldehydes. Of the various polymers of this type which have been investigated, only two are currently of appreciable commercial importance, namely urea-formaldehyde and melamine-formaldehyde polymers. In addition, melamine-phenol-formaldehyde and benzoguanamine-formaldehyde polymers find limited application. In the past there has been some commercial interest in thiourea-formaldehyde and aniline-formaldehyde polymers but these products are now of little importance. The aforementioned polymers form the contents of this chapter. 

Aniline—formaldehyde resins were once quite important because of their excellent electrical properties, but their markets have been taken over by newer thermoplastic materials. Nevertheless, some aniline resins are stiU. used as modifiers for other resins. Acrylamide (qv) occupies a unique position in the amino resins field since it not only contains a formaldehyde reactive site, but also a polymerizable double bond. Thus it forms a bridge between the formaldehyde condensation polymers and the versatile vinyl polymers and copolymers. 

Isocyanates. The commodity isocyanates TDI and PMDI ate most widely used in the manufacture of urethane polymers (see also Isocyanates, organic). The former is an 80 20 mixture of 2,4- and 2,6-isomers, respectively the latter a polymeric isocyanate obtained by phosgenation of aniline—formaldehyde-derived polyamines. A coproduct in the manufacture of PMDI is 4,4 -methylenebis(phenyHsocyanate) (MDI). A 65 35 mixture of 2,4- and 2,6-TDI, pure 2,4-TDI and MDI enriched in the 2,4 -isomer are also available. The manufacture of TDI involves the dinitration of toluene, catalytic hydrogenation to the diamines, and phosgenation. Separation of the undesired 2,3-isomer is necessary because its presence interferes with polymerization (13). 

The term aminoplastics has been coined to cover a range of resinous polymers produced by interaction of amines or amides with aldehydes. Of the various polymers of this type that have been produced there are two of current commercial importance in the field of plastics, the urea-formaldehyde and the melamine-formaldehyde resins. There has in the past also been some commercial interest in aniline-formaldehyde resins and in systems containing thiourea but today these are of little or no importance. Melamine-phenol-formaldehyde resins have also been introduced for use in moulding powders, and benzoguanamine-based resins are used for surface coating applications. 

Table 11.2 outlines the uses of phenol. We will consider the details of phenol uses in later chapters. Phenol-formaldehyde polymers (phenolics) have a primary use as the adhesive in plywood formulations. We have already studied the synthesis of bisphenol A from phenol and acetone. Phenol s use in detergent synthesis to make alkylphenols will be discussed later. Caprolactam and aniline are mentioned in the following sections in this chapter. 

The two key isocyanates that are used in the greatest volumes for polyurethane polymers are toluene diisocyanate (TDl) and methylene diphenyl diisocyanate (MDl). Both isocyanates are produced first by nitration of aromatics (toluene and benzene, respectively), followed by hydrogenation of the nitro aromatics to provide aromatic amines. In the case of MDl, the aniline intermediate is then condensed with formaldehyde to produce methylene dianiline (MDA), which is a mixture of monomeric MDA and an oligomeric form that is typical of aniline/formaldehyde condensation products [2]. The subsequent reaction of phosgene with the aromatic amines provides the isocyanate products. Isocyanates can also be prepared by the reaction of aromatic amines with dimethylcarbonate [3, 4]. This technology has been tested at the industrial pilot scale, but is not believed to be practiced commercially at this time. 

The pyrazolone can be incorporated directly in the polymer by utilizing a polymer-forming derivative such as a 1 -(amino or hydroxy -phenyl)pyrazolone in a phenol (or aniline)-formaldehyde polymerization. Alternatively, the pyrazolone nucleus can be combined with a synthetic or natural polymer by reaction of a functional group in the pyrazolone with the polymer. Thus, a 1-formylphenyl type is used to form a polyvinyl acetal. A compilation of such reactions is given in Part 1, Chapter II, Section 14, pp. 108-110. 

The first commercially successful synthetic polymer was phenol-formaldehyde (PF) resin (Smith 1899). The resin was introduced in 1909 by Baekeland as Bakelite . The urea-formaldehyde (UF) resins were discovered in 1884, but production of Beetle moldable resin commenced in 1928. Three years later, Formica , phenolic paper covered with decorative layer protected by UF, was introduced. The thiourea-formaldehyde molding powders were commercialized in 1920, while in 1935, Ciba introduced Cibanite , aniline-formaldehyde (AF) resins, molding materials, and then, 2 years later, the melamine formaldehyde (MF). 

Phenol-formaldehyde was reported as the first commercially synthetic polymer (1899) which was introduced as BakeliteT by Baekeland in 1909. This was the period which marked the dawn for the production of commercial synthetic thermosetting polymers. Other advances in the field included the discovery of urea-formaldehyde resins in 1884 and the beginning of their commercialization as Beetle moldable resin in 1928, followed by thiourea-formaldehyde (1920), aniline-formaldehyde (Cibatine by Ciba, 1935) and melamine-formaldehyde (1937) moulding powders. The year 1909 marked the discovery of epoxy compounds by Prileschaiev, which were not used until World War 2. The first thermoset polyesters, invented by Ellis, date back to 1934 and in 1938 was reported their first use in the forms of glass-reinforced materials [1]. 

Primary aromatic amines react with aldehydes to form Schiff bases. Schiff bases formed from the reaction of lower aUphatic aldehydes, such as formaldehyde and acetaldehyde, with primary aromatic amines are often unstable and polymerize readily. Aniline reacts with formaldehyde in aqueous acid solutions to yield mixtures of a crystalline trimer of the Schiff base, methylenedianilines, and polymers. Reaction of aniline hydrochloride and formaldehyde also yields polymeric products and under certain conditions, the predominant product is 4,4 -methylenedianiline [101 -77-9] (26), an important intermediate for 4,4 -methylenebis(phenyhsocyanate) [101-68-8], or MDI (see Amines, aromatic amines, l thylenedianiline). 

The polymer industry requires large quantities of 4,4 -diaminodiphenyl-methanes. These compounds are used in various applications as polymer additives. Currently they are manufactured by the acid-catalysed condensation of anilines with formaldehyde but like so many reactions of this type, the processes require the neutralisation of waste acid leading to large amounts of salt waste. Cleaner processes are required and solid acids offer a way forward. One potentially useful example of this is the aqueous reaction of aromatic anilines adsorbed on kaolinite with formaldehyde which cleanly give the desired products (Figure 3.5).36 In a typical experiment, the clay is stirred with water before aniline is added to the stirred solution. To this is slowly added formaldehyde solution. The precipitated 4,4 -diaminodiphenylmethane can be extracted in hot ethanol in a yield of 96%. Similarly, several substituted analogues have been prepared in yields of 70-99%. 

A simple way to produce polymers with specific nitrogen functions in controlled concentration is to prepare phenol-formaldehyde resins in which part of the phenol is substituted by aniline (for amine-type nitrogen) or... 

The primary use for phenol is as an intermediary chemical, a compound used in the synthesis of other chemicals. About 40 percent of all the phenol produced in the United States is used to make hisphenol A, while a similar amount is used in the production of a variety of polymers, such as phenol-formaldehyde plastics and nylon-6. The third largest application of phenol is in the manufacture of a host of other chemicals, xylene and aniline being the most important. 

Theoretically, the condensation of aniline with formaldehyde proceeds in the same way. In this case, the aromatic ring acts as a suitable nucleophilic reaction partner in acid media cross-linked polymers can arise because of the substitution possible in two o and one p positions, and also because of the bifunctionality of the amino group. The monomeric unit here can be represented schematically as... 

Amino polymers are derived from various amines and formaldehyde. Example amines used for these polymers are urea, benzoguanamine, melamine, and aniline, with the most common forms being urea and melamine resins. The formation of amino resins is complex, because the addition and condensation products of the amine and formaldehyde take multiple pathways involving by-products and side reactions. There is no general formula for a urea-based resins. The early reaction products are similar to those formed in phenolic resins or polyurethanes, but these early reaction products react further to form the final high polymer. Only the final reaction products will be considered in this section. 

Aniline and formaldehyde form resinous products under various conditions by means of rather ill-defined reactions. In a typical commercial process, aniline (1 mole) is treated with hydrochloric acid and then with formalin (1.2 mole formaldehyde). The resulting orange-red solution is fed into aqueous sodium hydroxide to precipitate a yellow material. This product has limited thermoplasticity but may be used to mould simple shapes. The material has good electrical insulation properties but has been largely superseded by polymers which are easier to process. 

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