Thermal rearrangement in thermal cascade reaction polymers via ortho-carbonate ester functionalization of polyimides and their gas separation performance

• Published in: Journal of membrane science 2022-08, Vol.655, p.120586, Article 120586
• Main Authors: Meis, David, Neumann, Silvio, Filiz, Volkan
• Format: Article
• Language: English
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2022.120586

Thermal Rearrangement Polymers have a strong potential regarding to gas separation membrane materials, especially for the purification of methane containing gas streams, due to their inter-connected bottleneck-type pores. However, most TR polymers reveal high permeabilities and high conversions only at high temperatures of 450 °C. Our study demonstrates a method to enhance the permeability at lower annealing temperatures by tailoring the thermally triggered decomposition and reaction cascade via modification and temperature protocol. In this study a set of seven carbonate ester modifications was prepared and thermo-analytically studied by means of DSC and TGA-FTIR on-line analysis combined with structure determination methods and quantum mechanical simulations. Two decarboxylative alkyl-transfer reaction mechanisms were formulated for the decomposition reaction of the carbonate ester group. A correlation of the size and branching of the carbonate ester connected alkyl group and its effect on the film properties and gas separation performance was studied. High polyimide to polybenzoxazole conversions were determined for the modified polymers and a 2008 upper bound performance was obtained for all materials, after annealing at 400 °C. Furthermore, the ethyl carbonate ester (ECO3PI-1) polymer entered the target zone above an ideal selectivity of CO2/CH4 of 30 after aging, making it an attractive membrane material. [Display omitted] •Synthesis of 6FDA-BisAPAF polymers.•In this study a set of eight carbonate ester modifications was prepared and studied.•High polyimides to polybenzoxazole conversions were determined for the new polymers.•Functionalization of the precursor polyimide were esterified.