Stabilization methods polymeric polyamides

Another method of achieving the desired molecular weight is by addition of a small amount of a monofunctional monomer, a monomer with only one functional group. Acetic acid or lauric acid, for example, are often used to achieve molecular weight stabilization of polyamides. The monofunctional monomer, often referred to as a chain stopper, controls and limits the polymerization of bifunctional monomers because the growing polymer yields chain ends devoid of functional groups and therefore incapable of further reaction. Thus, the use of benzoic acid in the polyamide synthesis yields a polyamide (XI) with phenyl end groups that are unreactive toward polymerization. 

Another polypyrrole/polyamide composite film was obtained by the electrode coating method [84]. In this work the polyamide film was obtained in situ by coating a stainless steel electrode with a polyamic acid film followed by imidization with pyridine and acetic anhydride. The coated electrode was submitted to a constant current in a pyrrole/LiC104 solution in acetonitrile. The surface conductivity measured after detaching the composite film from the electrode showed a strong dependence on the charge density used in the synthesis, i.e. on the amount of pyrrole polymerized in the composite. The maximum value obtained was 2 S cm . Combination of polypyrrole with this polyamide was shown to increase markedly its thermal and environmental stability. 

The use of tetracarboxylic acid anhydride instead of the dicarboxylic acids used in the manufacture of polyamides yields polyimides. The general method of preparation of the original polyimides by the polymerization of pyromellitic dianhydride and aromatic diamine is shown in Figure 1.18a. A number of diamines have been investigated, and it has been found that certain aromatic amines, which include m-phenylendediamine, benzidine, and di-(4-aminophenyl)ether, give polymers with a high degree of oxidative and thermal stability. 

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