The 4-[4'-(Hydrazinocarbonyl)phenoxy]-2-pentadecylbenzohydrazide was polycondensed with aromatic diacid chlorides viz., terephthalic acid chloride (TPC), isophthalic acid chloride (IPC), and a mixture of TPC : IPC (50 : 50 mol %) to obtain polyhydrazides which on subsequent cyclodehydration reaction in the presence of phosphoryl chloride yielded new poly(1,3,4-oxadiazole)s bearing flexibilizing ether linkages and pentadecyl side chains. Inherent viscosities of polyhydrazides and poly(1,3,4-oxadiazole)s were in the range 0.530.66 dL g(-1) and 0.490.53 dL g(-1), respectively, indicating formation of medium to reasonably high molecular weight polymers. The number average molecular weights (M-n) and polydispersities (M-w/M-n) of poly(1,3,4-oxadiazole)s were in the range 14,660-21,370 and 2.22.5, respectively. Polyhydrazides and poly(1,3,4-oxadiazole)s were soluble in polar aprotic solvents such as N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, and N,N-dimethylformamide. Furthermore, poly(1,3,4-oxadiazole)s were also found to be soluble in solvents such as chloroform, dichloromethane, tetrahydrofuran, pyridine, and m-cresol. Transparent, flexible, and tough films of polyhydrazides and poly(1,3,4-oxadiazole)s could be cast from N,N-dimethylacetamide and chloroform solutions, respectively. Both polyhydrazides and poly(1,3,4-oxadiazole)s were amorphous in nature and formation of layered structure was observed due to packing of pentadecyl chains. A decrease in glass transition temperature was observed both in polyhydrazides (143-166 degrees C) and poly(1,3,4-oxadiazole)s (90-102 degrees C) which could be ascribed to internal plasticization effect of pentadecyl chains. The T-10 values, obtained from TG curves, for poly(1,3,4-oxadiazole)s were in the range of 433-449 degrees C indicating their good thermal stability. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 124:1281-1289, 2012