However, this cost comparison overlooks stability differences. Previous studies have demonstrated that functionalization of polyamines with 2-hydoxybutyl improves the cyclic stability, and Goeppert et al. also established the stability of pentaethylenehexamine (PEHA) and tetraethylenepentamine (TEPA) functionalized with 2-hydroxypropyl (HP). Similar enhancement in stability is expected for HP-functionalized PEI. To confirm, we evaluated the working capacity of unmodified PEI and 0.10HP-PEI over 20 cycles (Fig. ). The cycles consisted of 60 minutes of adsorption (35 °C, 400 ppm CO2 in N2) followed by 10 minutes of desorption (90 °C, N2).