Hyper-Cross-Linked Polymers with Sulfur-Based Functionalities for the Prevention of Aging Effects in PIM-1 Mixed Matrix Membranes

The instability of gas permeation rates over time in PIM-1-based membranes is one of the obstacles preventing the implementation of this technology on larger scales. The addition of porous materials to the PIM-1 matrix is a known process to reduce aging effects in PIM-1-based membranes. Many porous solids of various chemical natures have been tested, ranging from inorganic to inorganic–organic hybrids to completely organic materials. Here, we report on the synthesis of two hyper-cross-linked polymers (HCPs) based on the diphenyl sulfide monomer, synthesized in either dichloromethane at 35 °C or dichloroethane at 78 °C. Two mixed matrix membranes (MMMs) were obtained from the addition of 3 wt % of either filler to PIM-1. Both the CO2 permeation rates and the CO2/N2 selectivity were measured for the pure PIM-1 membrane and for the two MMMs over a period of 400 days. PIM-1 exhibits a classic aging behavior with an 85% drop in the CO2 permeation rate with respect to the initial value. For the two MMMs, a retention of 50% of the initial CO2 permeability was instead observed after more than 400 days of aging. Despite the low surface area and low pore volume of the fillers, we show that diphenyl sulfide-based HCPs can reduce the aging rate in PIM-1 membranes.