Nylon-salt-type monomers

Rapid Synthesis of Polyimides from Nylon-Salt-Type Monomers... 

However, the starting point of polyimide synthesis dates away back to the mid 1950s, when Edwards and Robinson had synthesized aliphatic-aromatic polyimides (hereafter referred to as aliphatic polyimides) by the melt polycondensation of nylon-salt-type monomers composed of aliphatic diamines and aromatic tet-racarboxylic acids or their diacid-diesters (Eq. 2) [6,7]. 

Nevertheless, further detailed information was unavailable on the polyimide synthesis from nylon-salt-type monomers that is referred to as salt monomer method , and this method was not really recognized as a simple synthetic method of both aromatic and aliphatic polyimides. In addition, many polyimide investigations have mainly been concentrated on aromatic polyimides, and little information is available about aliphatic polyimides [13-18] that are also potential candidates for engineering plastics. 

First, the nylon-salt-type monomers such as XPME [20], XTPE [21, 22], and ODPME [23] with exactly 1 1 composition were prepared from a series of aliphatic diamines (X standing for the number of methylene unit) or aromatic bis(4-aminophenyl) ether (ODA) and the corresponding aromatic tetracarbox-ylic acid half diesters (diacid-diesters) such as pyromellitic acid diethyl ester (PME) and 3,3",4,4"-p-terphenyltetracarboxylic acid diethyl ester (TPE). 

Polyamides have been synthesized under microwave conditions from both fa-amino acids and Nylon-salt-type monomers, and polyimides have been obtained from salt monomers comprising aliphatic diamines and pyromellitic acid or its diethyl ester or derivatives of pyromellitic acid chlorides and aromatic diamines in the presence of a small amount of an organic solvent [1]. 

In the series of papers, synthesis of aliphatic polyamides and polyimides under microwave irradiation was described by Imai et al. [67-71]. The reactions were carried out in a modified domestic microwave oven with a small hole on the top of the oven so that nitrogen was introduced to a 30 ml wide-mouth vial adapted as a reaction vessel. In the case of polyamides synthesis, they were prepared of both CO-amino acids and nylon salt type monomers while polyimides were obtained from the salt form of monomers composed of aliphatic diamines and pyromellitic acid or its diethyl ester in the presence of a small amount of a polar organic medium (Fig. 11). 

Another way for synthesis of polyimides from Nylon-Salt-Type Monomers has been reported from Imai [4]. The method based on the melt polycondensation of diamine and pyromellitic acid half diester (pyromellitic add diethyl ester) (Scheme 3). 

Yoshio Imai (1999) Rapid Synthesis of Polyimides from Nylon-Salt-Type Monomers. In Progress in Polyimide Chemistry I. FI.R. Kricheldorf editor. Springer, pp. 3-20. 

Synthesis using tetracarboxylic dithioanhydrides [26,27] instead of tetracarboxylic dianhydrides and the high-pressure synthesis from nylon-salt-type monomers composed of diamines and tetracarboxylic acids [28-32] have also been reported. 

The synthesis of aliphatic polyamides under microwave irradiation has already been reported in a number of papers. " Polyamides were prepared from both co-amino acids and diamines together with dicarboxylic acids (i.e., the nylon salt-type monomers) in the presence of a small amount of a polar organic medium (Figure 32). 

Pyromellitic acid (PMA) was prepared by a usual hydrolysis of pyromellitic dianhydride, purified by sublimation, with water. 1,4-Diethyl ester of pyromelitic acid, i.e. 2,5-di(ethoxycarbonyl)terephthalic acid (PME), was synthsized according to the reported procedure (21) by the reaction of PMDA with absolute ethanol. A series of nylon-salt-type monomers XPMA and XPME, where X stands for the number of methylene unit in the aliphatic diamine, were prepared by a usual procedure by mixing an ethanol solution of an aliphatic diamine with an ethanol solution of PMA and PME, respectively, followed by recrystallization of the resultant precipitates with water (22,23). 

Polyimide Synthesis from Nylon-Salt-Type Monomers. The microwave-assisted polycondensation was further applicable to the effective, rapid synthesis of aliphatic polypyromellitimides from the salt monomers XPMA and XPME composed of aliphatic diamines and both pyromellitic acid PMA and its diethyl ester PME (Eqs 3 and 4). 

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