Accelerated Physical Aging of Thin Poly[1-(trimethylsilyl)-1-propyne] Films

Abstract

We present results for physical aging of films made from a high free volume polymer (poly[1-(trimethylsilyl)-1-propyne], PTMSP). Aging was tracked by gas permeation measurements of He and N2. The intermediate and thin films (3 and 1 μm) showed a rapid loss of gas permeability with time while the thick film (85 μm) showed no significant permeability change over more than 200 h. The permeability loss accelerated with decreasing thickness. The films were carefully conditioned to imprint a reproducible history. We conclude that bulk PTMSP apparently exhibits stable permanent gas permeabilities, but thin films appear prone to accelerated physical aging. This complements our earlier observations on a number of polymers. The results further support the hypothesis that free volume from the glassy material is eliminated over time at the surface of the films in a diffusion-like process.

Polymers of Intrinsic Microporosity

“…This accounts for the large variation in reported gas permeation data for PIM-1 [93,103,117]. In particular, residual solvent from casting and ageing of films, the latter a phenomenon shown by all glassy polymers especially those with high free volume [118], cause a reduction in permeability. Therefore, in order to allow a fair comparison between PIMs, it is best to use methanol treatment of the polymer film to ensure removal of casting solvent and to "reset" the ageing clock.…”

Gas permeation and physical aging properties of iptycene diamine-based microporous polyimides

“…Microporous glassy polymers typically undergo physical aging, or a physical densification of the polymer matrix in which the chains gradually assume a tighter packing arrangement [29,30]. Non-equilibrium excess free volume resulting from casting procedures or methanol treatment is dissipated and large reductions in permeability along with increases in selectivity are often reported.…”

Insight into reverse selectivity and relaxation behavior of poly[1-(trimethylsilyl)-1-propyne] by flux-lateral force and intrinsic friction microscopy

“…In a previous study, it has been shown that helium permeability decreases strongly with decreasing film thickness [38]. Thus, we should expect the permeation value of sequence 2, which is only 4400 barrer, to exceed the 5200 barrer value of sequence 1.…”

“…Clearly this is not the case. However, the important difference relative to the earlier study [38] is that in sequence 2, the membrane was exposed to CO 2 prior to helium permeation, building a barrier for helium to pass through the membrane, as has been seen in mixed gas experiments [7].…”

“…As there is some evidence that interfacial constraints play an important role in gas permeation of PTMSP nanocomposite systems [38], internal submolecular relaxations within PTMSP thin films were explored by IFA. An enthalpic activated process of 6-8 kcal/mol has been discovered, which could be attributed based on conformational calculations to local rotation of methyl groups along the PTMSP backbone.…”