Biobased Polycarbonate as a Gas Separation Membrane and “Breathing Glass” for Energy Saving Applications

The biobased poly(limonene carbonate) (PLimC) synthesized by catalytic copolymerization of trans‐limonene oxide and CO₂ unifies sustainability, carbon capture and utilization of CO₂ in one material. Films of PLimC show surprisingly high gas permeation and good selectivity. Additionally, it is not only very permeable to gases, but also to light, while simultaneously being a good heat insulator and mechanically strong, representing a novel type of material that is defined here as “breathing glass.” Hence, this study investigates the gas permeation and the selectivity in detail. The selectivity of PLimC for CO₂ can be understood by its high fractional free volume, which is determined by positron annihilation lifetime spectroscopy supported by simulations. The CO₂ permeability of PLimC at 30 °C is 68 barrer, while the CO₂/N₂ selectivity is ≈19, which places PLimC in a promising position in the Robeson plot and makes it unique due to its excellent transparency and processability under ambient conditions. Based on the high permeability of PLimC to gases and light, this study discusses here a completely new potential application of light transparent, gas‐permeable polymer films as “breathing glass.”