Dominique Gomes

Study of the synthesis of poly(4,4′-diphenylether-1,3,4-oxadiazole) in solutions of poly(phosphoric acid)

Abstract Using statistical design of experiments, samples of poly(4,4′-diphenylether-1,3,4-oxadiazole)s, POD–DPE, were synthesized through solution polycondensation of 4,4′-diphenylether dicarboxylic acid, DPE, and hydrazine sulphate, HS, in poly(phosphoric acid), PPA, under different reaction conditions. Final polymer molecular structure (average molecular weights, polymer composition, amount of hydrazide groups) is shown to depend strongly upon the polymerization conditions and that adequate properties for membrane synthesis (high average molecular weight, low amounts of hydrazide groups and low gel contents) can only be obtained if high synthesis temperatures (160°C) are used. Empirical and semi-theoretical models are developed to describe the kinetics of POD–DPE production in PPA solutions, showing that the likely existence of cross-linking reactions may explain both the relatively high values and the large fluctuations of the average molecular weight obtained experimentally.

Synthesis and characterization of flexible polyoxadiazole films through cyclodehydration of polyhydrazides

Abstract Aiming to produce flexible films of poly(4,4′-diphenylether-1,3,4-oxadiazole), POD-DPE, the synthesis of POD-DPE through thermal cyclodehydration of polyhydrazide in solutions of poly(phosphoric acid), PPA, and in film form is studied here. It was observed that POD-DPE polymer samples obtained when the cyclodehydration of polyhydrazide is performed in solutions of PPA are insoluble in the solvents normally used for film preparation. On the other hand, the cyclodehydration of polyhydrazide in film form can lead to brittle POD-DPE films due to the high temperatures required for reaction to occur. In order to obtain flexible POD-DPE films with high conversion through cyclodehydration of polyhydrazide films, it is shown here that it is very important to adjust the cyclodehydration temperature ( T c ) as a function of the glass transition temperature ( T g ) and the weight average molecular weight ( M w ) of the polyhydrazide. In all cases analyzed, polyhydrazides were synthesized by low temperature solution polycondensation reactions and were characterized by intrinsic viscosity measurements, size exclusion chromatograpy, nuclear magnetic resonance, infrared spectroscopy and thermal analysis. Polyhydrazides with weight average molecular weights up to 74,100 g/mol were obtained. The POD-DPE films obtained were characterized by infrared spectroscopy and nuclear magnetic resonance, showing that the production of POD-DPE films is indeed possible from cyclodehydration of polyhydrazide films.

Determination of hydrazide content in poly(oxadiazole-hydrazide) copolymers by NMR and thermal analysis

Abstract A new technique based on nuclear magnetic resonance (NMR) is developed in this paper to determine quantitatively the hydrazide content in poly(oxadiazole-hydrazide) copolymers. Two-dimensional 1H–13C shift correlation and 1H NMR spectra of poly(4,4′-diphenylether-1,3,4-oxadiazole-hydrazide) copolymers with different hydrazide contents were performed to characterize these copolymers and allow for development of a NMR based quantitative correlation for hydrazide content. Thermal gravimetric measurements (TGA) were also performed in order to provide an independent data set for validation of the NMR based technique. The results obtained with the proposed NMR technique were shown to be in good qualitative agreement with the TGA results.

Evaluation of parameter uncertainties during the determination of the intrinsic viscosity of polymer solutions

Abstract In this work, it is shown that quadratic approximations of the function that relates the viscosity of polymer solutions with the polymer concentration lead to values of the intrinsic viscosity that are much more uncertain than the values obtained through simpler linear fits. Therefore, in spite of the expected better interpolations provided by second-order approximations, statistical arguments show that the use of linear fits is advisable when the number of experimental points available for the determination of intrinsic viscosities is small. Experimental data available for solutions of poly(4,4′-diphenylether-1,3,4-oxadiazole)s, POD-DPE, in sulfuric acid are used to illustrate this point.