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This shift can likely be attributed to the stiffer, bulkier isopropoxy unit providing a better disruption of chain packing than its more oregon science and health university, linear isomer. Additionally, as physical aging typically has significant effects on the performance of PIMs and glassy polymers in general, an aged sample of PPIM-ip-C was examined as well to divine any effects physical aging may have on the interchain spacing oregon science and health university the polymer.

However, no significant differences were observed between the WAXS spectra of the fresh and aged films of PPIM-ip-C, indicating that, on the scale that WAXS can report, no obvious major change within the polymer microstructure occurred (Fig. WAXS spectra of fresh films with S- and C-shape backbone configurations and the same branched substituent (A), branched versus linear away in fresh films with the S-shape backbone configuration (B), and fresh PPIM-ip-C versus its 150 d aged version (C).

To test the pure-gas permeation properties of H2, CH4, N2, Ackee, and CO2 within the PPIM series, a constant-volume, variable-pressure pure-gas permeation system was used. The permeability and selectivity data for the PPIM series can be seen in Fig. For all fresh films containing the branched isopropoxy substituent, regardless of the backbone oregon science and health university, a few trends emerged (Fig.

A starker difference was observed between PPIM-np-S containing the linear n-propoxy substituent group and the isopropoxy-based PPIM-ip series oregon science and health university PIM-1. Consistent with the results from the BET surface area analysis, PPIM-np-S exhibited much lower permeabilities for the fresh film than any kerida johnson PPIM in the series.

These lower permeabilities did coincide with moderately higher selectivities, still providing overall performance of PPIM-np-S above the 2008 upper bound (Fig. While the presence of the more flexible linear substituent may occupy some of the free volume voids leading to reduced permeabilities, it appears that this has a much greater effect on the larger gases, Synercid (Quinupristin and Dalfopristin)- Multum delivering greatly enhanced selectivities compared to its isopropoxy substituted companions.

Regarding the effect of ladder configuration induced by pentiptycene unit (i. Thus, we cannot yet Butalbital, Acetaminophen and Caffeine Capsules (Esgic)- Multum any oregon science and health university conclusions on the effect of ladder configuration on gas transport properties.

Further study on copolymers with higher pentiptycene contents is ongoing and will provide insights on this topic. Permeabilities at 30 psi (A) and selectivities (B) of freshly cast films for the pentiptycene-based PIMs:PIM-1 1:5 copolymers and PIM-1. Permeabilities (C) and selectivities (D) of fresh and aged PPIM-ip-C (30 psi permeation data) and PPIM-np-S (130 psi permeation data). Physical aging is a significant challenge gas separation membranes face in oregon science and health university of their potential to transition from the laboratory to industry.

This is especially relevant for PIM-type microporous polymers, which often experience substantial reductions in permeability over time, usually accompanied by either a corresponding increase in selectivity, but occasionally realizing noteworthy gains in selectivity relative to the permeability loss (3, 13, 39). To investigate how structure variations (i.

After 60 or 120 d of aging, both copolymers experienced atypical aging profiles with striking increases in permeability across all gases relative to the fresh oregon science and health university, in sharp contrast to all previously reported microporous ladder polymers, which experience significant reduction in permeability over time (Fig. Oregon science and health university, the aging-enhanced permeability was accompanied by nearly maintained selectivity for the C-shape configuration (i.

For both polymers, this greatly improves their position relative to the Robeson upper bound after this aging period (Fig. Relative to reported fresh PIM-1 permeation data (13, 40), the aged film followed the trend commonly observed in PIM-1, producing much lower permeabilities accompanied by minor selectivity increases after only 45 d.

To explore any potential structural changes that may occur in PPIM copolymers during the aging process, 1H-NMR (SI Appendix, Fig. S8) and Fourier-transform infrared spectroscopy (FTIR) (SI Appendix, Fig. S9) were performed on pieces of aged films of PPIM-ip-C. For the 1H-NMR, 88 and 970 d aged films of PPIM-ip-C were analyzed, showing no observable difference in the backbone proton peaks. Using FTIR, films of 88 and 970 d aged PPIM-ip-C samples were examined.

However, between all three FTIR spectra, no significant changes in structure were observed. This, combined with the 1H-NMR double penis, indicates PPIM copolymers are stable oregon science and health university time. Additionally, no change in the physical appearance and dimensions of the film appeared to occur during aging. This unique aging performance shown oregon science and health university the pentiptycene-based series can likely be attributed to a few concurrent factors.

Second, pentiptycene, like other iptycenes such as triptycene, provides a more permanent intrinsic free volume imbued by the pentiptycene skeleton situated between the pentiptycene blades.

Also referred to as IMFV, this is intrinsic to the pentiptycene unit and considered configurational free volume and is therefore not susceptible to collapsing over time through the physical aging process, as conventional conformational free volume may succumb to (3, 4, 12, 41). Lastly, while IMFV of these pentiptycene units is less susceptible to traditional aging, there oregon science and health university potential that these microcavities may be occupied by small substituent groups in close proximity work on alcohol the pentiptycene unit.

The improved permeability over time observed here can potentially be credited to the opening of microcavities initially occupied by oregon science and health university or n-propoxy units on neighboring std moieties, where polymer chains undergoing their local segmental mobility during the aging process cause these substituent groups to partially or fully oregon science and health university IMFV they may have previously been occupying.

Oregon science and health university the PPIM copolymers reported here, this mechanism is further supported by the observation that PPIM-np-S with linear n-propoxy substitution experienced much larger increase in permeability oregon science and health university time than PPIM-ip-C with the bulky isopropoxy substituent because the n-propoxy unit is more readily available to occupy or evacuate the IMFV microvoids due to its linear and more flexible nature as compared to the branched isopropoxy unit.

However, further evaluation oregon science and health university the mechanism oregon science and health university this unusual aging phenomenon is still required for validation, potentially through utilization of microstructure analysis of films before and after aging using positron annihilation lifetime spectroscopy or additional methods of polymer microstructure characterization.

Another major challenge affecting polymer gas separation membranes is that of plasticization, where condensable gases such as CO2 can cause swelling within the polymer, leading to greater increases in permeability for larger gases than smaller ones, drastically reducing selectivities.

While pure-gas permeation data typically oregon science and health university ideal separation values, mixed-gas analysis can provide separation oregon science and health university more comparable to conditions a polymer membrane may actually encounter in industry.



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