Abstract
In the present work, a set of anthracene maleimide monomers with different aliphatic side groups obtained by Diels Alder reactions were used as precursors for a series of polymers of intrinsic microporosity (PIM) based homo- and copolymers that were successfully synthesized and characterized. Polymers with different sizes and shapes of aliphatic side groups were characterized by size-exclusion chromatography (SEC), (nuclear magnetic resonance) 1H-NMR, thermogravimetric (TG) analysis coupled with Fourier-Transform-Infrared (FTIR) spectroscopy (TG-FTIR) and density measurements. The TG-FTIR measurement of the monomer-containing methyl side group revealed that the maleimide group decomposes prior to the anthracene backbone. Thermal treatment of homopolymer methyl-100 thick film was conducted to establish retro-Diels Alder rearrangement of the homopolymer. Gas and water vapor transport properties of homopolymers and copolymers were investigated by time-lag measurements. Homopolymers with bulky side groups (i-propyl-100 and t-butyl-100) experienced a strong impact of these side groups in fractional free volume (FFV) and penetrant permeability, compared to the homopolymers with linear alkyl side chains. The effect of anthracene maleimide derivatives with a variety of aliphatic side groups on water vapor transport is discussed. The maleimide moiety increased the water affinity of the homopolymers. Phenyl-100 exhibited a high water solubility, which is related to a higher amount of aromatic rings in the polymer. Copolymers (methyl-50 and t-butyl-50) showed higher CO2 and CH4 permeability compared to PIM-1. In summary, the introduction of bulky substituents increased free volume and permeability whilst the maleimide moiety enhanced the water vapor affinity of the polymers.
Highlights
Membrane technology has drawn great attention owing to its advantages of being ecologically favorable, cost-efficient and easy to operate
After the successful conversion of tetramethoxy to tetrahydroxy anthracene, a Diels-Alder reaction was carried out using maleimides, which contain different substituents attached to the nitrogen atom
Anthracene maleimide-based comonomers with different alkyl side chains were successfully synthesized by the Diels-Alder reaction. 1H Nuclear Magnetic Resonance (1H-NMR) and TG-FTIR characterizations of comonomers were properly established
Summary
Membrane technology has drawn great attention owing to its advantages of being ecologically favorable, cost-efficient and easy to operate. Polymers are encouraging materials for gas separation membranes due to their benign processability and low upscaling costs [1]. There are two significant parameters that define membrane performance, permeability (P) and selectivity (α = PA/PB). The selectivity parameter, is an indirect function of solubility and diffusivity of the membrane. The aforementioned transport parameters are directly affected by the state and microstructure of the membrane material; it is crucial to develop tailored polymers for gas separation application [3]. Glassy polymers are used for the separation of non-condensable gases, and for these polymers, a trade-off between permeability and selectivity is known to cause limits to the use of polymers in practical gas separation [4]. Gas transport takes place through interconnected free volume elements formed by non-perfect packing of macromolecular chains of amorphous polymers
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