Abstract
The last decade has seen an exponential increase in the number of studies focused on novel applications for ionic liquids (ILs). Blends of polymers with ILs have been proposed for use in fuel cells, batteries, gas separation membranes, packaging, etc., each requiring a set of specific physico-chemical properties. In this work, blends of four grades of the poly(ether-ester) multiblock copolymer PolyActive™ with different concentrations of the CO2-philic 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [BMIM][Tf2N] were prepared in the form of dense films by a solution casting and solvent evaporation method, in view of their potential use as gas separation membranes for CO2 capture. Depending on the polymer structure, the material properties could be tailored over a wide range by means of the IL content. All samples were dry-feeling, highly elastic self-standing dense films. The microstructure of the blends was studied by scanning electron microscopy with a backscattering detector, able to observe anisotropy in the sample, while a special topographic analysis mode allowed the visualization of surface roughness. Samples with the longest poly(ethylene oxide terephthalate) (PEOT) blocks were significantly more anisotropic than those with shorter blocks, and this heterogeneity increased with increasing IL content. DSC analysis revealed a significant decrease in the melting enthalpy and melting temperature of the crystalline PEOT domains with increasing IL content, forming an amorphous phase with Tg ≈ −50 °C, whereas the polybutylene terephthalate (PBT) phase was hardly affected. This indicates better compatibility of the IL with the polyether phase than the polyester phase. Young’s modulus was highest and most IL-dependent for the sample with the highest PEOT content and PEOT block length, due to its high crystallinity. Similarly, the sample with short PEOT blocks and high PBT content also showed a high modulus and tensile strength, but much lower maximum elongation. This study provides a detailed discussion on the correlation between the morphological, thermal, and mechanical properties of these PolyActive™/[BMIM][Tf2N] blends.
Highlights
Polyethene oxide terephthalate-polybutylene terephthalate (PEOT-PBT) multiblock copolymers are well-known semi-crystalline polymers commercialized under the name PolyActiveTM
The haze was caused by the phase separation of the polymer in micrometer-sized crystalline PBT domains and amorphous or semi-crystalline poly(ethylene oxide terephthalate) (PEOT) domains
Comparing the membranes on the basis of their composition, the neat polymers P1 and P2 have a finer microstructure than polymers P3 and P4, which have a much larger PEOT phase than the PBT phase
Summary
Polyethene oxide terephthalate-polybutylene terephthalate (PEOT-PBT) multiblock copolymers are well-known semi-crystalline polymers commercialized under the name PolyActiveTM. Their application ranges from pharmaceutics [1,2] and medicine [3,4] to gas separation membranes [5,6]. Poly(ethylene oxide) (PEO)-based membranes have been recognized as promising materials for CO2 separation [7]. Bondar et al [10] reported CO2 /H2 selectivities of 9.8 and CO2 /N2 selectivities of 56, with CO2 permeability coefficients of approximately 220 Barrer in polyether-b-polyamide segmented block copolymers. Car et al [11], for the PEOT-PBT copolymer, reported a CO2 permeability of 115
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