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Polymers with intrinsic microporosity (PIMs) are of great interest in the field of gas separation membranes. Already the first synthesized PIM-1 shows extraordinary permeability and selectivity. Unfortunately, PIM-1 is susceptible to physical aging and thus gradually loses its outstanding properties. In this study a polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) was used as a nanofiller (0–40 wt%) in the PIM-1 matrix to potentially improve the gas transport properties and prevent physical aging. The molecular mobility of the solution-cast nanocomposite films was analyzed by Broadband Dielectric Spectroscopy (BDS). Furthermore, gas permeability was determined with the time lag method (0–20 bar upstream pressure) at 35 °C for N2, O2, CH4 and CO2.
Especially now, in times of the energy revolution, the need for energy efficient separation processes promote the advancement of new high performance materials for use as highly selective separation membranes. Most promising materials in this field, especially for gas separation, are polymers with intrinsic microporosity (PIMs) which were firstly introduced by Budd and McKeown. Currently widespread application of PIMs for membrane technology is still restrained by their strong tendency to physical aging involving a significant loss of their good gas separation properties. This phenomenom is directly related to the molecular mobility. Here for the first time, molecular dynamics and conductivity in PIM-1, the first synthesized PIM, were investigated by broadband dielectric spectroscopy (BDS). Although an α-relaxation was not observed for PIM-1, as a thermal glass transition temperature has not yet previously been reported below its decomposition temperature at 370°C, surprisingly a conductivity contribution was found which is attributed to intermolecular agglomerates formed by π−π-stacking. Besides the studies on pure PIM-1 a polyhedral oligomeric phenethyl-silsesquioxanes (PhenethylPOSS) was used as nanofiller (0 – 40 wt%) in order to evaluate its ability to improve gas transport properties and probably control physical aging. The molecular mobility of all materials was analyzed by BDS of solution-cast films.
In times of the energy revolution, the need for energy efficient separation processes promotes the advancement of new high performance materials for use as highly selective separation membranes. Most promising materials in this field, especially for gas separation, are polymers with intrinsic microporosity (PIMs) which were firstly introduced by Budd and McKeown. In this study the permeability of PIM-1 was increased by 439 % by formation of nanocomposites with only 1 wt% of polyhedral oligomeric phenethyl-silsesquioxane (PhE-POSS) within the polymer matrix. As the CO2/CH4 selectivity is fully retained, this leads to a shift in the Robeson plot towards the upper bound. The Robeson plot describes the current state of the art trade-off relation between selectivity and permeability of all known membrane polymers. As molecular mobility is a key factor for gas transport as well as the often observed physical aging of such polymers, our study also includes for the first time, molecular dynamics and conductivity of pure PIM-1 and PIM-1 nanocomposites as investigated by broadband dielectric spectroscopy (BDS).