Abstract
It is well known that 4,4'hexafluoro isopropylidene-phthalic anhydride(FDA) has higher permeability and selectivity. It is contributed to –CF group contained in polyimide structure material. In this study, the diffusion properties of a,w-bis(3-aminopropyldimethyl) oligodimethylsiloxane (ODMS) fragment impact on 6FDA were studied. Molecular simulation techniques and Grand canonical Monte Carlo(GCMC)calculations were adopted for predicting the permeability of C2H5OH and H2O in the three new polymers membranes. The membranes considered in this work were synthesized from 6FDA and ODMS. The sorption and diffusion properties of C2H5OH and H2O were calculated. The results show that the 6FDA/6ODMS presents higher permeability than 6FDA/2ODMS and 6FDA/4ODMS. With the longer of ODMS segments in the repeat units, the permeability and selectivity of C2H5OH/H2O increase in the order of 6FDA/2ODMS< 6FDA/4ODMS< 6FDA/6ODMS. The length of molecular chains becomes longer with the ODMS fragments increased, which leads to the gap between the molecular chains becoming larger. Due to the free volume in the system increases, it is more conducive to the larger molecular volume through the membrane. Hence, it can be predicted that the 6FDA/6ODMS is the best for the separation of C2H5OH/H2O.
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