The bisesterdiamide T4T dimethyl tone and a half repeat units of 1,4-butylene terephthalamide, nylon-4,T) (benzoic acid, 4,4＇-[1,4-butanediylbis(iminocarbonyl)]bis-, dimethyl ester, CAS no. 1028 10-33-3) has been synthesized from an excess of dimethyl terephthalate and 1,4-butanediamine. Lithium methanolate was used as a catalyst. Different solvents have been used to optimize the yield and purity. A pure product could be obtained by recrystallization from hot NMP. D.s.c. and n.m.r. analyses were used to determine the purity of the product. The melting temperature of the T4T dimethyl (T-m = 265 degrees C) decreased with increasing loss of uniformity. The T4T dimethyl showed a transition in the crystalline structure upon heating at 160-175 degrees C.