Ultrahigh Free Volume Polymers

Because the so-called ultrahigh free volume polymers aroused much interest during the last 10 years, they will be briefly described in this introductory chapter. The publication of the physical properties of poly(l-trimethylsilyl-l-propyne) (PTMSP) in 1983 [281] aroused much interest in the field of membrane research. Up to this time it had been believed that the rubbery poly(dimethyl si-loxane) has by far the highest gas permeability of aU known polymers. Very surprisingly, the glassy PTMSP showed gas permeabilities more than 10 times higher than PDMS. This could be attributed to its very high excess-free volume and the interconnectivity of the free volume elements. Since then a number of 

Polymer Oxygen permeability (Barrer) Oxygen/nitn n selectivity 

It will be quite interesting to observe which class of polymers will finally be applied for the attractive field of hydrocarbon dewpointing of natural gas. The superglasses like PMP show the highest selectivities and fluxes. However, due to their double bonds their chemical stability remains uncertain and they might be prone to physical aging, which is the irreversible absorption of components 

Polymer Permeability (Barrer) Mixed-gas selectivity Mixed gas/pure gas 

It has been reported recently that flux and even selectivity of PMP and PTMSP can be enhanced by the addition of nanoparticles (285, 286]. Merkel et al. [285] added fumed sihca to PMP and observed a simultaneous increase of butane flux and butane/methane selectivity. This unusual behavior was explained by fumed-silica-induced disruption of polymer chain packing and an accompanying increase in the size of free volume elements through which molecular transport occurs. Gomes et al. [286] incorporated nanosized sihca particles by a sol-gel technique into PTMSP and found also for this polymer a simultaneous increase in flux and selectivity. It has to be studied, if physical aging of the polyacetylenes is reduced by the addition of nanoparticles. 

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Table 1.1 contains typical solubility prediction data for an ultrahigh free-volume polymer (PTMSP) and a polymer with more conventional transport properties (PTMSS). 

The fact that for the mentioned ultrahigh free-volume polymers the continuous hole-phase peak appears at rather limited values is related with the limited size of the... 

Figure 1.7 then shows respective data for an ultrahigh free-volume and performance polymer, Teflon AF2400 of DuPont (P02 = 1140 Barrer [39]). One can recognize that... 

Hofmann, D., Enhialgo-Castano, M., Lebret, A., Heuchel, M., and Yampolsldi, Y., Molecular modeling investigation of free volume distributions in stiff chain polymers with conventional and ultrahigh free volume comparison between molecular modeling and positron lifetime studies. Macromolecules, 36, 8528-8538 (2003). 

D. Hofmann, M. Heuchel, Y. Yampolskii, V. Khotimskii, V. Shantarovich, Free volume distributions in ultrahigh and lower free volume polymers Comparison between molecular modeling and positron lifetime smdies. Macromolecules, 35, 2129-2140 (2002). 

Hofmaim, D., et al.. Molecular Modeling Investigation of Free Volume Distributions in Stiff Chain Polymers with Conventional and Ultrahigh Free Volume Comparison Between Molecular Modeling and Positron Lifetime Studies. Macromolecules, 2003, 36(22), 8528-8538. 

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