Effect of Uniform Deformation on the Mechanical and Gas Transport Characteristics of Polyimides Based on Diethyltoluylenediamine

It has been shown that uniform biaxial deformation leads to an increase in the elastic modulus and a simultaneous increase in gas permeability coefficients of films of amorphous polyimides (PIs) based on a mixture of diethyltoluylenediamine isomers and 6FDA, BPDA, and BPADA dianhydrides compared with non-deformed samples. At the same time, for PI based on BPDA dianhydride, the diffusion coefficients of gases remain unchanged, and for PIs based on 6FDA and BPADA dianhydrides, a decrease in diffusion coefficients is observed. Thus, an increase in gas permeability with uniform biaxial deformation is explained by an increase in the gas solubility coefficients for all PIs. A decrease in the diffusion coefficients for PIs based on 6FDA and BPADA dianhydrides is accompanied by an increase in the selectivity of diffusion, which is interpreted as ordering of the chains packing in the polymer matrix. A joint analysis of mechanical and gas transport characteristics shows that the greatest ordering of chain packing is observed for PI based on BPADA dianhydride; this ordering is less obvious for PI based on fluorine-containing 6FDA dianhydride; and the ordering of chain packing is insignificant or absent at all for PI based on rigid BPDA dianhydride.