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PRINCIPAL PUBLICATION AND AUTHORS

Controlled grafting of multi-block copolymers for improving membrane properties for CO2 separation, X. Solimando (a), J. Babin (a), C. Arnal-Herault (a), D. Roizard (b), D. Barth (b), M. Ponçot (c), I. Royaud (c), P. Alcouffe (d), L. David (d), A. Jonquieres (a), Polymer 255, 125164 (2022); https:/doi.org/10.1016/j.polymer.2022.125164 (a) Université de Lorraine, CNRS, LCPM, Nancy (France) (b) Université de Lorraine, CNRS, LRGP, Nancy (France) (c) Université de Lorraine, CNRS, IJL, Nancy (France) (d) Laboratoire Ingénierie des Matériaux Polymères (IMP), Université Claude Bernard Lyon 1, Univ. Lyon, CNRS UMR 5223 (France)

REFERENCES

[1] Sixth Report of the Intergovernmental Panel on Climate Change (IPCC); https:/www.ipcc.ch/report/ar6/wg3/downloads/report/ IPCC_AR6_WGIII_Full_Report.pdf [2] S.L. Liu et al., Prog. Polym. Sci. 38, 1089-1120 (2013). [3] A. Kargari et al., J. Ind. Eng. Chem. 84, 1-22 (2020). [4] M. Kárászová et al., Sep. Purif. Technol. 238, 116448 (2020). [5] X. Solimando et al., Polymer 131, 56-67 (2017).

synthesis of a new functional poly(urea/urethane-imide) (PUI) copolymer with PEO-based Jeffamine CO2-philic soft blocks and a small monomer unit containing alkyne side groups allowing their grafting by click chemistry. Small CO2-philic oligomers containing a complementary terminal azido group were obtained as graft precursors, by controlled radical polymerisation (SET-LRP) for the precise control of their molecular weight from 2000 to 5000 g/mol. The grafting of these CO2-philic oligomers was then achieved by quantitative click chemistry, allowing a good control of the number of CO2-philic grafts.

The grafted multi-block copolymers combined highly permeable CO2-philic soft blocks and soft grafts with highly rigid urea/urethane-imide hard blocks. These quasi-impermeable hard blocks were responsible for strong physical cross-linking, allowing the simple casting of membranes from copolymer solutions. The morphology of the related non-grafted multi-block copolymers was formerly investigated [5] and was typical for PEO-based multi-block copolymers [2-3]. When the PEO-content was increased, a phase separation of the soft and hard blocks occurred, but the PEO-based soft blocks did not crystallise. This nanophase separation contributed to high CO2 permeability obtained at the expense of a strong decrease in selectivity. The morphology of the new grafted multi-block copolymers was very different from that of the related non-grafted multi-block copolymers, allowing to overcome the former limitation.

The special morphology of the new grafted multi-block copolymers was investigated by direct imaging of the membranes by transmission electron microscopy, differential scanning calorimetry and indirect techniques including small-angle X-ray scattering (SAXS) experiments performed at beamline BM02 D2AM for

the characterisation of different membranes at the nanoscale (Figure 129). These experiments showed that the CO2-philic soft blocks and grafts did not crystallise (a great advantage for CO2 capture) and formed a single nanophase that increased in size and fraction with the number and molecular weight of the CO2-philic grafts. In addition, such analyses revealed that the hard blocks bearing the soft grafts were dragged into the new soft phase, leading to a nanodispersion of impermeable obstacles in the highly permeable phase. Therefore, the grafting of multi-block copolymers induced a specific morphology allowing the simultaneous increase of their soft phase content and tortuosity for gas permeation.

The membrane properties were determined by time- lag gas permeability experiments with CO2 and N2 pure gases at 2 bar and 35°C, in conditions appropriate for CO2 post-combustion capture from flue gases. The grafting of the multi-block copolymer was responsible for a strong improvement of the CO2 permeability up to 196 Barrer. At the same time, the membrane ideal separation factor was maintained at high level (αCO2/N2 = 39) due to the special morphology of the grafted multi-block copolymers. Some hard blocks finely dispersed in the soft phase indeed limited the diffusion of the biggest molecules (N2) and the high membrane selectivity remained quasi-constant.

Finally, the best membrane showed properties among the best-reported so far for PEO-based copolymer membranes for CO2 capture. In the close future, the new advanced design of CO2-philic copolymer membranes could open new opportunities for developing polymer blends and nanocomposites with CO2-philic charges (so called mixed matrix membranes) with very high features for CO2 capture.