(401ag) The Effects of Chemical Structure on Gas Transport Properties in a Family of Polyethersulfones Polymers

Ali Naderi¹, Wai Fen Yong¹, Youchang Xiao¹ and Tai-Shung Chung^{1, *}

Martin Weber², Christian Maletzko³,

¹Department of Chemical and Biomolecular Engineering, National University of Singapore,

Singapore 117585, Singapore

²Advanced Materials & Systems Research, BASF SE, GMV/W - B001, 67056 Ludwigshafen, Germany

³Performance Materials, BASF SE, G-PM/PU, 67056 Ludwigshafen, Germany

*Correspondence author. Tel: +65 6516 6645; fax: +65 67791936.

E-mail address: chencts@nus.edu.sg(T.-S. Chung).

Abstract

Polymeric membranes are considered as a promising technology for gas separation. Polysulfone (PSF) and polyethersulfone (PES) have been used in the membrane applications due to their thermal stability, chemical resistance, processability and intrinsic properties. In this work, a series of BASF polyethersulfones polymers containing of different backbone structures have been studied. Their permeation, sorption properties and physical properties were investigated. The gas permeabilities of the dense films including oxygen, nitrogen, methane, and carbon dioxide were measured as a function of pressure. The sorption of methane and carbon dioxide were assessed via the dual-volume pressure decay method using a XEMIS microbalance system and the diffusion coefficients of these gases through the membranes were determined by solution-diffusion model. The permeability of the membranes decreases slightly with the increase in pressure for all gases which can be due to the saturation of Langmuir sites in high pressure. To elucidate the microstructural behavior of different PES, positron annihilation life time spectroscopy (PALS) and dynamic mechanical analyses (DMA) have been examined. The results of PALS and DMA reveal that the polyphenylsulfone (PPSU) with a higher segmental motion in the polymer chain offers a higher free volume which subsequently lead to a higher CO₂ and CH₄ diffusion rates through the membrane. Among all the PES, the trimethyl polyethersulfone (TPESU) shows the highest CO₂ and CH₄ sorption. The high CO₂ and CH₄ sorptions in the TPESU could be attributed to the high polymer chain-penetrant interactions of this polymer compared to the others. The diffusivity coefficients of CO₂ of each membrane in the Henry and Langmuir sites have been calculated according to the dual mode sorption and the immobilization models. The results reveal that a higher mobility of the Langmuir site than the Henry site in the PPSU compared to the others. These results are in accordance with the γ-transition results that have been obtained via DMA analyses.