High free volume polymers

These high-free-volume polymers also have unusual permeability characteristics with mixtures of condensable and noncondensable gases. For example, in the presence of as little as 1200 ppm of a condensable vapor such as the per-fluorocarbon FC-77 (a perfluoro octane-perfluoro decane mixture), the nitrogen permeability of PTMSP is 20 times lower than the pure nitrogen permeability [71], as shown in Figure 2.41. When the condensable vapor is removed from the feed gas the nitrogen permeability rapidly returns to its original value. The best... 

Table 3.5 Permeability coefficients P (Barter) of high free volume polymers with respect to hydrocarbons (at 1 atm)...

An interesting peculiarity that can be potentially important from the practical viewpoint is solubility-eontrolled seleetivity of some high permeability, high free-volume polymers revealed in separation of hydroearhons aecording their molecular mass. As permeability eoeffieients ean be presented as the product P = DS, the variations of the P values for the series of penetrants ean be ascribed to corresponding trends of the D and S values [31]. 

This work offers a contribution to the understanding of some fundamental aspects of sorption and diffusion in glassy polymers. The research focuses on an extensive experimental study of sorption and mass transport in a specific polymeric matrix. A high free volume polymer, (poly l-trimethylsilyl-l-propyne) [PTMSP], has been used here in order to emphasise aspects of sorption and transport which are peculiar to polymer/penetrant mixtures below the glass transition temperature. The discussion of the experimental data presented in this work permits a clarification of concepts which are of general validity for the interpretation of thermodynamic and mass transport properties in glassy systems. 

The PAL spectrum of polystyrene, which is considered as a conventional glassy polymer, is also presented in Table I for comparison. It is seen that much longer lifetimes (5-7 ns for X4) are characteristic of high permeability materials. Interestingly, such long lifetimes have been observed as well in silicagels and zeolites (76) or even in porous UF membranes as is shown below. All of this information is in line with the assunq)tion that high free volume polymers like PTMSP are akin to porous sorbents (probably with open or closed porosity). 

A fundamental result of the PALS studies of high free volume polymers such as PTMSP, amorphous glassy teflons AF, as well as microporous PPO menibranes is that the size distribution of FV in these materials is bimodal and not monomodal as in conventional glassy and rubbery polymers. It will be useful in the future to compare the results of the application of different programs (CONTIN, MELT) for hole size distribution in samples with well defined microstructure, such as zeolites, in order to check the findings of the PALS method. 

Thick film, i.e. bulk, samples are typically used when screening the transport properties of polymeric membrane materials, due to ease of handling and creation of defect-free films. Except for ultra-high free volume polymers such as... 

When the high free volume polymer PMP is combined with inorganic nanoparticles, an increase in vapor-gas selectivity was also repotted (Merkel et al., 2003a). For PTMSP combined with inorganic nanoparticles, different results on selectivity have been published... 

Plate, N.A., Yampolskii, Yu., High Free Volume Polymers. In Polymer Gas Separation Membranes, D.R. Paul, Yu. Yampolskii, eds. CRC Press, London, 1994. 

---