Influence of the molecular structure of polybinaphthalene on the membrane separation performance

• Published in: European polymer journal Vol. 101; pp. 248 - 254
• Main Authors: Monga Mulunda, Mikael, van Goethem, Cédric, Zhang, Zidan, Nies, Eric, Vankelecom, Ivo, Koeckelberghs, Guy
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.04.2018; Elsevier BV
• Subjects: Binaphthalene dihedral angle; Bridged binaphthalene; Carbon dioxide; Cotton; Dihedral angle; Ethylene; Gas separation; Gas separation performance; Membrane separation; Molecular chains; Molecular structure; Polybinaphthalene; Polybinaphthalene membrane; Polymers; Propylene; Bridged binaphthalene; Polybinaphthalene; Polybinaphthalene membrane; Gas separation performance; Binaphthalene dihedral angle
• ISSN: 0014-3057; 1873-1945
• DOI: 10.1016/j.eurpolymj.2018.02.034

To study the influence of the molecular structure of polybinaphthalene on the gas separation membrane properties, a binaphthalene is bridged with four different linkers (methylene to butylene) and copolymerized with two co-monomers of different length. However, the linkers do not significantly change the binaphthalene dihedral angles as reported previously. Consequently, the polybinaphthalene have similar macromolecular structure as demonstrated by CD spectroscopy and DFT calculations. These results confirm the similar gas selectivities observed with the polybinaphthalene membranes. Moreover, the influence of the co-monomer length on the membrane separation is not noticed. [Display omitted] •Binaphthalene bridged with these linkers, methylene, ethylene, propylene and butylene result in the binaphthalene monomers with a similar dihedral angle.•Polybinaphthalene synthesized from these monomers have similar macromolecular structures.•The similarity in the macromolecular structures result in a same packing of the polymers in the membranes.•Therefore the membranes have the same free-volumes and the same gas separation performances. A chiral binaphthalene is bridged at the 2,2′-positions with methylene (CH2), ethylene (C2H4), propylene (C3H6) and butylene (C4H8) linkers, with the aim to vary the binaphthalene dihedral angle and hence to study the influence of the latter on the polybinaphthalene gas separation membrane performances. It was hypothesized that different angles would induce different membrane performances. The polymer membranes with the four different linkers show average gas selectivities, CO2/CH4 = 22 ± 3 and CO2/N2 = 28 ± 2, which strongly indicates that these polymers have strongly similar macromolecular structures. This is confirmed by CD spectroscopy which reveals the same Cotton effect patterns. The similarity in the macromolecular structures can be ascribed to a smaller than anticipated change in the dihedral angle introduced by the linkers, 4° of difference between ethylene, propylene and butylene, as demonstrated by DFT calculations.