One-Pot Synthesis of Copoly(Aliphatic-Aromatic)Oxadiazoles: How to Control the Formation of Random or Block Structures?

The polyoxadiazole synthesis in P2O5/CH3SO3H solution has been improved by precipitation of the reaction mixture in cold NMP. The polyoxadiazole obtained by this process did not contain uncyclized hydrazide moieties and was more stable in strongly acidic media. This process has been used to prepare some copolyoxadiazoles with dodecanedioic and isophthalic diacids or dihydrazides. The microstructure of the copolymers (alternate versus block) depends on the nature of the isophthalic derivative. With isophthalic dihydrazide, which is soluble in the reaction mixture like the dodecanedioic derivative, an alternate structure is obtained. With isophthalic diacid, which exhibits low solubility, the dodecanedioic derivate first reacts giving an aliphatic oxadiazole sequence and finally a block copolymer is obtained. The microstructure was determined by proton NMR spectroscopy allowing us also to calculate the average sequence length.