I was reading about carbon polymers and noticed something interesting about the difference between the reaction used to form nylon and the reaction used to form aramids: in the former, the monomers are an amine and a carboxylic acid, while in the later the monomers are an aromatic amine and an aromatic acyl halide.
Adipic acid, used to create Nylon 66
This struck me as interesting because it seems like the reaction should be roughly the same for the creation of either polymer, with the only difference being the presence of the aromatic ring in the aramid in place of a simple carbon chain. Is the halide required for polymerization in the aramid, but not the nylon, or is there another, perhaps economic, reason for its use? Why are halides used in the creation of aramids, but not in simpler nylons?