Block copolymer pervaporation membranes with microphase separated structures for ethyl acetate separation

A series of multiblock polydimethylsiloxane-b-polyimides copolymers, including non-fluorinated (PDMS-b-PI) and fluorinated polyimides (PDMS-b-FPI), were successfully prepared from pyromellitic dianhydride and 4,4′-(4-aminophenoxy) biphenyl, 4,4′-(hexafluoroisopropyl) diphenyl dicarboxylic anhydride and 2,2′-bis(trifluoromethyl)benzidine, respectively. The chemical structures of these block polymers were determined with FTIR. Self-supporting membranes were prepared from the copolymers using a solution coating method. The physicochemical properties, pervaporation properties and thermal stability of the block polymer membranes were studied. The results showed that the mechanical properties of PDMS-b-FPI and PDMS-b-PI membranes increased with an increase in the FPI or PI content in the copolymer, where the tensile strengths and moduli increased, and the elongations at break decreased. The swelling of the PDMS-b-FPI and PDMS-b-PI membranes in ethyl acetate increased with an increase in the PDMS content, and membranes with PDMS contents of less than 50% were stable. TEM showed that the block copolymers formed microphase separated structures. SAXS showed that the chain segment spacing increased with the increase of PDMS content, and the chain segment spacing of PDMS-b-FPI was larger than that of PDMS-b-PI. In the pervaporation tests using a feed solution containing 5 wt% ethyl acetate at 40 ℃, the separation factor(α) of the PDMS-b-PI-50 membrane was 31, and the total flux(J) was 924 g·m⁻²·h⁻¹. Using the same pervaporation test conditions, the α of the PDMS-b-FPI-50 membrane was 31, and the J was 1267 g·m⁻²·h⁻¹. Both the PDMS-b-PI-50 and PDMS-b-FPI-50 membranes were found to be stable during the separation tests, and the α and J did not change significantly after 150 min of operation.