Volume glassy polymers

M. G. Baschetti, F. Doghieri, B. Freeman, G. C. Sarti, Transient and steady-state effective diffusivity in high free volume glassy polymers, J. Membr. Sci., 344, 144—154 (2009). 

V. Shantarovich, I. Kevdina, Yu. Yampolskii, A. Alentiev, Positron annihilation lifetime study of high and low free volume glassy polymers effects of free volume size on the permeability and permselectivity. Macromolecules, 33, 7453-7466 (2000). 

The ability of limiting aging phenomena in high free volume glassy polymers is a recent discovery for hybrid membranes and can open up a new branch of study for this polymers family. If selectivity enhancement via the sieving mechanisms and antiaging properties of the fillers can be coupled with the high transmembrane flux offered by the polymer phase, superior separation features can be achieved. 

Wang, X. Y, et al. (2004). Cavity Size Distributions inHighFree Volume Glassy Polymers by Molecular Simulation. Polymer, 45(11), 3907-3912. 

Poly(4-methyl-2-pentyne) [PMP] is a glassy, disubstituted, purely hydrocarbon-based polyacetylene. PMP has a density of only 0.78 g/cm and a high fractional free volume of 0.28. The polymer has very high hydrocarbon permeabilities for example, the /i-butane permeability of PMP in a mixture of 2 mol% n-butane in methane is 7,500 X lO l cm3(STP) cm/cm2 s cmHg at 25 C. In contrast to conventional, low-free-volume glassy polymer membranes, PMP is significantly more permeable to n-butane than to methane in gas mixtures. In this paper, we present the gas permeation properties of PMP in mixtures of -butane with methane. The mixed-gas permeation and physical aging properties of PMP are compared to those of poly(l-trimethylsilyl-l-propyne), the most permeable polymer known. 

The n-butane/methane selectivity increased monotonically from 8 to 24 as the feed temperature was decreased from 50 to 2°C, as shown in Figure 5. It is important to note that both n-butane permeability and n-butane/methane selectivity increased in the PMP membrane as the feed temperature decreased. This temperature/permeability behavior is completely different from that in low-free-volume glassy polymers used... 

By this method also, polymer/silica nanocomposites have been fabricated [165,166]. Merkel et al. discovered that the addition of nanometer-sized fumed silica particles to certain high-free volume, glassy polymers could systematically increase gas permeability. Such high-permeability polymers included poly(4-methyl-2-pentyne) (PMP), poly[l-(trimethyl-silyl)-l-propyne] (PTMSP), andpoly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene) [107]. 

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