Amphiphilic micelle-forming PDMS-PEGBEM comb copolymer self-assembly to tailor the interlamellar nanospaces of defective poly(ethylene oxide) membranes

An amphiphilic comb copolymer was synthesized via free-radical polymerization using two macromonomers: monomethacryloxypropyl-terminated poly(dimethyl siloxane) (PDMS-MA, 10,000 g mol⁻¹) and poly(ethylene glycol)–behenyl ether methacrylate (PEGBEM, 1500 g mol⁻¹). The PDMS-PEGBEM comb copolymer underwent self-assembly to form micellar structures in ethanol/tetrahydrofuran solvent. The micelle-forming PDMS-PEGBEM copolymer was incorporated into the low-cost, commercially available polymer, and non-selective polymer poly(ethylene oxide) (PEO, 10⁶ g mol⁻¹), resulting in highly selective all-polymeric membranes. The alignment of the PDMS-PEGBEM micelles in the interlamellar region of PEO and the corresponding increase in the domain spacing were observed by transmission electron microscopy and small-angle X-ray scattering, confirming the successful encapsulation of PDMS-PEGBEM in the interlamellar region. The PDMS functions as a rubbery filler between the crystallites, whereas PEGBEM has good affinity towards PEO because of their chemical similarity. The CO₂/N₂ and CO₂/CH₄ selectivities of PEO membranes was significantly enhanced from 0.78 and 0.71 to 41.7 and 13.3, respectively, on the loading of 10 wt.% of the copolymer. The highest CO₂ permeability reached 240 barrer at 50 wt.% copolymer loading, with the CO₂/N₂ and CO₂/CH₄ selectivities of 34.6 and 12.2, respectively. Herein, the evolution of the interlamellar nanospaces and dual-phase region, as well as the microstructures of the membranes are reported.