Piperazinium-mediated crosslinked polyimide-polydimethylsiloxane (PI-PDMS) copolymer membranes: the effect of PDMS content on CO 2 separation.

We synthesized copolymers consisting mostly of physically stable rigid polyimide (PI) and a low content of highly permeable rubbery polydimethylsiloxane (PDMS), that were crosslinked by CO 2 -philic ionic piperazinium groups attached to the side chains of the copolymers. These crosslinked copolymers (xPI-PDMSs) were fashioned into membranes that showed very high levels of thermochemical stability and excellent CO 2 separation performance ( P CO 2 of 799 Barrer and CO 2 /N 2 permselectivity of 15.7). The inclusion of the piperazinium groups not only endowed these xPI-PDMS membranes with increased selectivity for CO 2 , but also good resistance to CO 2 plasticization. The effect of PDMS content on morphology and CO 2 separation properties of xPI-PDMS was also investigated.