Monofunctional acid

Acidolysis, Aminolysis, and Alcoholysis. When heated, polyamides react with monofunctional acids, amines, or alcohols, especially above the melt temperature, to undergo rapid loss of molecular weight (58,59), eg, as in acidolysis (eq. 3) with acetic acid [64-19-7] or aminolysis (eq. 4) with an ahphatic amine ... 

The addition of small, but specific, amounts of a monofunctional acid to the polymerization is often used to control molecular weights and catalyze reactions. The polymerization is controlled to produce a number-average molecular weight of 18,000—30,000, depending on the end use. 

The potentiometric titration curves of gels, which relate the pH of the exterior solution to the degree of ionization of the gel, resemble the titration curves of monofunctional acids or bases. However, the dissociation constants differ, often by two orders of magnitude, from the expected value for the functional group, and the slope of the curves is not the usual one. Addition of neutral salt changes the picture markedly and brings the curves closer to expectation. In the case of weak or medium... 

Equation (38) gives an explanation for the curves reported in different salt solutions At high salt concentration the potential goes to zero and cq- approaches cq-, so that both terms diminish and the titration curve approaches that of a monofunctional acid. At low salt concentrations the potential is high and the Donnan distribution requires ccr >... 

Since the molecular weight of this nylon-6,6, produced by Carothers, was higher than he desired, 1% acetic acid (a monofunctional acid that acted to terminate chain growth) was added, resulting in a product with a lower molecular weight and a melting point of about 200°C. 

Molecular weight control and stabilization are accomplished by addition of a calculated amount of a monofunctional acid such as acetic acid. Diamine loss during polymerization is unavoidable because of its volatility. The loss must be quantitatively taken into account by careful control of process conditions and initial charges of reactants. 

As discussed in Section 2.5.1, extensive research in the field of aromatization have resulted in the development of commercial processes, the Mobil M2 forming,219 the Cyclar (UOP-BP),172 the Aroforming (IFP-Salutee),395 and the Alpha (Sanyo Petrochemical)396 processes. New reviews cover the fundamental and practical aspects of both monofunctional (acid-catalyzed) and bifunctional routes of aromatization.397-400 Further readings with respect to industrial applications may be find is symposia proceedings.401... 

Bis-substitution of stilbene produces stronger fluorescence and the bis-triazine derivatives of diaminostilbenes have proved to be the most successful brighteners for cellulosics, in particular, and polyamides (60MI11200). The variety of substitution permutations in (90) is almost endless and many primary and secondary homocyclic and heterocyclic amines, thiols and phenols have been used. Synthesis of such compounds is straightforward and utilizes the convenient selectivity to substitution of cyanuric chloride. 4,4 -Diaminostilbene-2,2 -disulfonic acid condenses readily at 0-5 °C with cyanuric chloride, under slightly acidic conditions. In this case cyanuric chloride behaves as a monofunctional acid chloride and, although some by-products are unavoidable, two molecules of cyanuric chloride condense... 

Carbonium ions and isoparaffins are formed by hydride ion abstraction and hydride ion transfer reactions. This mechanism has been described for HF.SbFg (5). Isomerization of n-paraffins over monofunctional acidic catalysts has also been claimed for mordenite (6, 7), for sieve Y (8), and for the base of the catalyst of undisclosed composition applied in the isomerization process using a noble metal on an acidic zeolite base (3). 

Alkyd Resins. Reaction product of a dibasic add and a polyol, to which sufficient monofunctional acid or alcohol has been added to prevent gelation during processing, Review Kraft, J. Am. Oil Chem. Soc. 39, 501 (1962). 

The P power is another quantity that is well defined in an Immobiline pH gradient. As for any solution containing weak monofunctional acids and bases, the buffering capacity is given by the equation... 

There are several satisfactory commercial ways to produce polycaprolactam (6-nylon). In one method, eaminocaproic iu id is used as a catalyst. Molten caprolactam with 1-5 per cent catalyst is heated at atmospheric pressure at 24Q-280°C for 6-8 hr. The vessel is blanketed with steam or nitrogen to prevent oxidation. At equilibrium, the pol3mier contains about 10 per cent of unreacted caprolactam. Use of a small amount of the monofunctional acid assists in stabilizing the molecular weight. 

Alkyd resins are based on polymeric resins developed in the 1920s. The first alkyd resins sold commercially under the name Glyptal were made by the General Electric Company (Fig. 3.20). Alkyd resins are a class of polyesters synthesized by condensation between an alcohol and an acid or anhydride. Actually, the anhydride is modified with a monofunctional acid, most commonly C g fatty acid, which can be obtained from vegetable oil (rubber seed oil (RSO) or palm oil) [61-63]. The major advantage of the alkyd resins is their components (fatty acids and triglyceride... 

Salt dehydration. Direct esterification requires high purity materials in equimolar amounts because esterifications rarely go beyond 98% completion in practice. To overcome this, hexamethylene diamine and a dibasic acid such as adipic acid can be reacted to produce a nylon salt, hexamethylene diammonium adipate. A solution of 0.5-mol diamine in a mixture of 95% ethanol (160 cm ) and distilled water (60 cm ) is added to 0.5-mol diacid dissolved in 600 cm of 95% ethanol over a period of 15 min. The mixture is stirred for 30 min during which time the nylon salt precipitates as a white crystalline solid. This can be recrystallized and should melt at 456 K. The pure salt can be converted into a polyamide by heating it under vacuum in a sealed tube, protected by wire gauze, at about 540 K in the presence of a small quantity of the diacid, e.g., 10 g salt to 0.55-g adipic acid is a suitable mixture. If a lower molar mass is desired, a monofunctional acid can replace the adipic acid and act as a chain terminator. 

The earlier alkyd resins (glyceryl phthalate) were all of the heat-convertible variety on heating the resin was converted to a nonfusible type [15]. More recently an unmodified alkyd refers to a resin prepared from a dibasic acid, a polyol, and an oil or fatty acid. In some cases a monofunctional acid such as benzoic acid has been added to reduce functionality [23], Oxygen- or air-convertible alkyd resins are prepared by replacing part of the polybasic acid with the proper amount of an oxidizable unsubstituted fatty acid or acids such a linolenic, oleostearic, or others that are commercially available. With these two types of systems, alkyds are used to prepare coatings that cure upon baking or air drying. 

Besides fatty acids, other monofunctional acids are often used in small quantities in certain alkyd resins (Figure 2.11). Rosin was initially used to modify the drying time of alkyd resins because of its... 

Figure 20 (A) A polysiloxane copolymer having benzoic acid sidechains complexed with a mesogenic chiral stilbazole derivative [105], (B) A dipyridil complexed with two monofunctional acids showing Tsn = 166.5°, Tni = 178.5°C. Compare with the open assembly in Fig. 2A (Ref. 7a).

Monofunctioning acids and bases A small discrepancy exists between the pK values calculated in the Tables of Chapter 2 and the standard values in the literature. For example, the pKa value for benzoic acid, calculated in Table 2.2 IS 4 16 0 01 at 20°C, (similarly we obtained 4 16 0 01 at 25 X), whereas the most highly regarded values are in the range 4 18 to 4 20 at 25" (Kortiini, etal., 1961). The reason for this discrepancy is that our calculations, up to this point, have included both concentration and activity terms, and our results for benzoic acid are mixed pKg values. These mixed constants, which we call K, are constant only for the concentration of ionized species at v. hich the pH was measured and stand in contrast to equation (31) in which all the terms are expressed as activities. The standard values for benzoic acid, on the other hand, have been calculated using activities throughout and the thermodynamic constant, KI, is entirely independent of concentration (see p. 2 and Appendix H). 

In general, divalent cations form stronger complexes with the monofunctional acid anions than with the difunctional acid anions and aromatic compounds. Typical speciation calculation results are shown in Figs. 2, 3, and 4. In all cases, the divalent ion is the predominant species at low... 

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