Diamines, aromatic diacid chloride reaction

Monomer structure can affect the competition between cyclization and linear polymerization. For example, phthalic acid (ortho isomer) is more prone to cyclization than terephthalic acid (para isomer) at the very-low-molecular-weight end, for example, the dimer stage. The ortho structure makes more likely the conformations that are more favorable for cyclization. Stiff linear chains such as those formed in the reaction between an aromatic diamine and aromatic diacid chloride are much less prone to cyclization than the flexible chains formed from the corresponding aliphatic monomers. 

Aromatic polyamides are generally made by low-temperature reactions of aromatic diamines and aromatic diacid chlorides in special solvents such as a 1 3 molar mixture of hexamethylphosphoramide A-methylpyrrolidone, as in reaction (4-50). Intensive stirring is required to attain high molecular weights because the polymer precipitates. These macromolecules are very rigid and rodlike. They form oriented liquid crystalline arrays in solution and require little postspinning orientation to produce extremely strong and stiff fibers. The polymer would not be made in the melt because it is infusible. It must be synthesized and handled in solution, and this requires the use of reactive precursors. 

Reaction of Acid Chlorides. Low-temperature polycondensation of diamines and diacid chlorides is an important route for preparing high-melting polyamides such as aromatic polyamides, which decompose or cross-link if prepared by high-temperature melt routes. The reaction may involve an interfacial reaction between the diacid chloride in a water-immiscible solvent with an aqueous diamine solution, or the reaction may be carried out in a homogeneous solution. The presence of a base is usually needed to remove HCl so that polymerization is complete. With weakly basic aromatic diamines, an acid acceptor is not always needed because HCl can be evaporated from the reaction mixture. The general reaction is given by... 

Vapor-phase polymerization has been described in the patent literature as an alternative route to aromatic polyamides from aromatic diamines and aromatic diacid chlorides [81]. The reaction is carried out in the gas phase by mixing vapors of the two monomers in the presence of an inert gas. The temperature at the reaction zone has to be higher than the glass transition temperature of the polymer to achieve segmental mobility of the growing polymer chain. 

Fully aromatic polyamides form from reactions of aromatic diacid chlorides and aromatic diamines. An example is formation of poly(m-phenylenediamine isophthalamide) ... 

Trimethylsylil-substituted amines undeigo a variety of reactions with electrophiles. This reaction was extended recently to preparations of high molecular weight aromatic polyamides by low temperature solution polycondensation. N-trimethylsilylated aromatic diamines were condensed with aromatic diacid chlorides at -10 T in an amide solvent ... 

Aromatic polyamides first appeared in the patent literature in the late 1950s and early 1960s, when a number of compositions were disclosed hy researchers at DuPont (1-3). These polymers were made by the reaction of aromatic diamines with aromatic diacid chlorides in an amide solvent. Over 100 examples of aromatic polymers and copolymers described in patents were listed in a 1989 book (4). Another extensive list of polymers was provided in the previous edition of this encyclopedia (5). 

The principal ingredients for the manufacture of aromatic polyamides on a commercial scale are the diamine and diacid chloride monomers, plus the solvents used for the polymerization reaction. The chemical processes reported to be used for preparation of each of these ingredients are described in this section. 

A 1965 book (21) discusses low temperature solution polycondensation at length, although it does not deal with the reaction of aromatic diamines with aromatic diacid chlorides by this method. The book also discusses interfacial polymerization. 

The most widely employed synthetic route to aramids is based on the polycondensation of dicarboxylic acids with diamines in the presence of condensing agents. Good reviews on the synthesis of aramids have recently appeared (1-3). Recently, promising alternative synthetic routes to aramids have been reported and are described herein. These include the polycondensation of N-silylated diamines with diacid chlorides, the addition-elimination reaction of dicarboxylic acids with diisocyanates, and the palladium-catalyzed carbonylation polymerization of aromatic dibromides, aromatic diamines and carbon monoxide. 

In 1973 Du Pont commenced production of another aromatic polytunide fibre, a poly-(p-phenyleneterephthalamide) marketed as Kevlar. It is produced by the fourth method of polyamide production listed in the introductory section of this chapter, namely the reaction of a diamine with a diacid chloride. Specifically, p-phenylenediamine is treated with terephthalyl chloride in a mixture of hexamethylphosphoramide and V-methylpyrrolidone (2 1) at -10°C Figure 18.32). 

It is also possible to prepare them from amino acids by the self-condensation reaction (3.12). The PAs (AABB) can be prepared from diamines and diacids by hydrolytic polymerization [see (3.12)]. The polyamides can also be prepared from other starting materials, such as esters, acid chlorides, isocyanates, silylated amines, and nitrils. The reactive acid chlorides are employed in the synthesis of wholly aromatic polyamides, such as poly(p-phenyleneterephthalamide) in (3.4). The molecular weight distribution (Mw/Mn) of these polymers follows the classical theory of molecular weight distribution and is nearly always in the region of 2. In some cases, such as PA-6,6, chain branching can take place and then the Mw/Mn ratio is higher. 

In 1951, Flory reported the condensation reaction of diacid chlorides, e.g. with potassium salts of imides, e.g. the condensation of sebacyl chloride with potassium phthalimide. In this way, A -acyl diimides are formed. Flory pointed out the possibility of forming polymers, when components with higher functionality are used. Poly(imide)s (PI)s from pyromeUitic acid were reported in 1955 by Edwards and Maxwell at DuPont. Tbe diamines used were of aliphatic nature. Later, in addition, aromatic diamines were used. The two major types of Pis are ... 

Three general methods are employed to form aromatic polyamide-imides [88]. The first one consists of an initial reaction of a mole of a diacid chloride with two moles of a diamine. The product is then reacted with a dianhydride and after that condensed to an imide ... 

The two-phase process occurs between the reaction of diacid chlorides and diamines dissolved in water and water-immiscible solvent media of low polarity, and low-molecular-weight PAs are formed due to rapid precipitation. A base and a surfactant are usually added to the aqueous media. The reaction is extremely fast and occurs in the interphase on the organic solvent side. The mixture of immiscible solutions, on rapid stirring, gives rise to a polymer precipitate. Wholly or partially water-miscible solvents have been found suitable for the synthesis of aromatic PAs. The main drawback of this method is that the precipitation of the growing polymer chains usually forms polymers with broad molecular weight distribution, and they are considered to be unsuitable for fibers or filmforming materials. 

Monomers derived from trimellitic anhydride, mainly V-carboxyphenyltrimel-litimides and V-(co-carboxyalkylene)trimellitimides have been also used many times as starting materials for the synthesis of poly (amide imide)s. These poly (amide imide)s have been traditionally prepared by low temperature solution polycondensation, from diamines and imide-diacid chlorides [182], but they have been also successfully synthesized by the phosphorylation method of direct polyamidation [184], from diamines and imide-diacids [185-188] as depicted in Scheme (36). Trimellitic acid imide (4-carboxyphthal-imide) has also been used for the preparation of poly(amide imide)s, by reaction with aliphatic and aromatic diamines in solution at moderate temperatures [189]. 

This reaction occurs rapidly in the presence of an acid acceptor under mild conditions. The conventional melt polymerization techniques, as used for the preparation of nylons, cannot be applied to aromatic polyamides since the melting points of the polymers are too high. Polymerization is therefore conducted either in solution (e.g., in methylene chloride) or in suspension. In the latter case, the diamine is dissolved in water, together with an acid acceptor (e.g., sodium carbonate) and the diacid chloride is dissolved in a solvent which is immiscible with water (e.g., carbon tetrachloride or cyclohexanone). The two solutions are then subjected to intensive mixing. Rapid reaction occurs at the liquid interface or just inside the solvent boundary and this technique is therefore commonly termed interfacial polymerization. 

The same research group [90] reported the preparation of OA (PAIs) derived from N,N-(4,4 -oxydiphthaloyl)-bis-(s)-(+)-valine diacid chloride. The polymers were prepared by the reaction of aromatic diamines with the diacid by classical low-temperature solution polycondensation (reaction time 2 h at -5°C and 8 h at rt), high-temperature polycondensation (reflux conditions, reaction time Imin), and MW polycondensation reaction (reaction time 6min). Comparable results were obtained for all polycondensation processes. 

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