Two-Step Aromatic Polyamide Networks

There are in the literature three reported methods to prepare two-step aromatic polyamide networks. Two of them use the reduction of a pendant nitro group to a reactive amine as a means to create reactive sites along the precursor chain. A U.S. patent by Erhan [614] claims the preparation of high molecular weight linear polyamide by either interfacial or solution polymerization of a single AB-type monomer with itself  

and other similar monomers, is prepared from the corresponding amino acid by reacting it with thionyl chloride and dry HCl [414,415]. The resulting poly(nitrobenzamide) is treated in a second step by reducing agents such as Sn -I- HCl, Zn + HCl and catalytic hydrogenation, to obtain the analogous poly(aminobenzamide)  

These linear chains were later crosslinked in a separate second step to form a crosslinked aromatic polyamide network. The crosslinking agents mentioned in the patent are categorized into four groups polyfunctional epoxides, dianhydrides, polyfunctional isocyanates and benzoquinone [614]. No additional information is given. 

It is interesting to note that Erhan [614] claims the polymerization of monomers such as 3-amino-5-nitro-diphenylcarboxylic acid 

A different method by Aharoni to create two-step rigid polyamide networks employs pendant carboxy groups on the precursor linear chains, instead of nitro or amine. One way of preparing such chains requires the preparation of diacid chloride monomeric species from excess terephthaloyl dichloride and DABA  

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The third method to create two-step aromatic polyamide networks is chemically similar to the one discussed above in Sect. 3.1.6.2. Here, a fraction of the terephthalic monomer in the reaction solution is replaced by 2,3-cyclobuta-terephthalic acid (619a). Upon polymerization a lyotropic aromatic polyamide is obtained which, when heated to 380 °C or higher, randomly crosslinks along the stiff chains to form a two-step network. Not much else is known at present about this system. 

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