Synthesis of amphiphilic PCZ-r-PEG nanostructural copolymers and their use in CO2/N2 separation membranes

摘要

Poly(ethylene glycol) (PEG) is considered a good candidate material for CO2 separation membranes due to its high affinity with CO2, but the preparation of a robust, free-standing PEG membrane is challenging. Although a crosslinking method is often used to prepare PEG membranes, it has limitations in process-ibility, in that it is only applicable to the coating layer. We report the synthesis of amphiphilic polycarbonate Z-r-poly(ethylene glycol) (PCZ-r-PEG) nanostructural copolymers with improved processibility and their application to CO2/N2 separation membranes. The copolymers were synthesized using bisphe-nol Z, triphosgene and PEG (2000 g/mol) via solution polycondensation polymerization, as confirmed by Fourier transform infra-red spectroscopy (FTIR), nuclear magnetic resonance (~1H-NMR) and gel permeation chromatography (GPC) analysis. Structural and morphological analysis was studied by transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). TEM images revealed a self-assembled, microphase-separated morphology in the hydrophilic rubbery PEG domains and the hydrophobic glassy PCZ domains, which is also supported by the existence of two glass transition temperatures (T_gs) in the DSC curves. The thermal stability of the PCZ-r-PEG copolymers was less than that of the PCZ homopolymer, but was quite stable up to around 350 °C. The mechanical properties of all the membranes were significant, with reduced elongation at break while the Young's modulus increased with PEG content. The PCZ-r-PEG copolymer exhibited a CO2 permeability of 50.7 Barrer (1 Barrer = 1 x 10~(-10) cm~3(STP)cmcm~(-2) s~(-1) cmHg~(-1)) and CO2/N2 selectivity of 42.25 at 35 °C and 2 atm, which was much greater than those of the PCZ homopolymer membrane (CO2 permeability of 2.7 Barrer, selectivity of 27).