1. INTRODUCTION
The two principal commercial polyamides are poly(hexamethylene adipamide) (nylon 66) and polycaprolactam (nylon 6). They are produced by direct amidation of a diacid with a diamine and ring-opening polymerization of ɛ-caprolactam, respectively. Poly(hexamethylene adipamide) is synthesized by hexamethylene diamine and adipic acid [1]. A stoichiometric balance of amine carboxylic group is readily obtained by the preliminary formation of a 1:1 ammonium salt: