Polymer membranes are of great technological interest for a range of molecular separations. The numerous polymers currently used as gas separation membranes have a tendency to result in permeability/selectivity relationships that are limited by an upper bound or Robeson line. Aromatic polyimides (PIs) can be used as a membrane material because of their outstanding set of physical properties. Polymers containing 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) are attractive due to their superior thermal properties, low flammability, organo-solubility, adhesion to metal and atomic oxygen resistance. Phosphaphenanthrene skeleton is relatively free of conformational stress that results in a large bulky structure which inhibits the packing of polymer chains. In the present investigation a phosphaphenanthrene skeleton containing diamine was synthesized that leads to a series of new processable PIs when reacted with several commercially available dianhydrides. The polymers were characterized thoroughly by different analytical techniques. The membranes were prepared directly by the thermal imidization of the poly(amic acid)s following a programmed heating up to 300 oC. The membranes were transparent and flexible. The PIs showed high glass transition temperature (Tg up to 261 oC), high thermal stability (up to 416 °C under air) and good mechanical properties (Tensile strength up to 91 MPa and elongation break up to 18 %). The membranes showed high gas permeability (PCO2 up to 175 and PO2 up to 64 barrer), high permselectivity (PCO2/PCH4 up to 51 and PO2/PN2 up to 10) and some of the polymers surpass the 2008 upper bound drawn by Robeson. Molecular dynamics simulation of the polymers were done using an atomistic model that showed good agreement between the size distribution free volume and gas transport properties. This study provides an insight on the diffusion behavior of gas molecules in polymer membranes and was consistent with the experimentally obtained diffusion behavior.

Polyimides with phosphaphenanthrene skeleton: Gas permeation study and molecular dynamics simulations

255th National Meeting (2018)

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