Monomer Reactivity and Steric Factors affecting the Synthesis of Aromatic Polyamides

A series of aromatic polyamides were synthesized by activation of aromatic diamines through a newly improved synthetic method. The polymers described herein were prepared by direct polycon-densation of isophthaloyl chloride (IPC) with silylated aromatic diamines prepared in situ by addition of chloro(trimethyl)silane (CTMS). Moreover, the same polycondensation reaction was carried out in a medium containing pyridine, to investigate the effect of the base as a promoter. The reactions were studied for diamines of different reactivity to demonstrate the feasibility of this synthetic method in polycondensation reactions. An interesting behavior was observed for sterically hindered, and therefore less reactive diamine, 4,4'-methylene-bis(2,6-dimethylaniline). The two activation methods here employed afforded readily polyamides having an inherent viscosity of 2.54 dL g-1 for the most reactive diamine (1a), when CTMS was used as the activating agent, and polyamides having an inherent viscosity of 0.65 dL g-1 for the sterically hindered diamine (1e), using the pair CTMS/Py as the activating agent. The experimental work was supported by calculations of the electronic parameters of the aromatic diamines, using quantum mechanical methods (DFT). Overall, this highly efficient one-pot method provides advantages through an easy handling and simple procedure.