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.