Fractional free volume PTMSP

Figure 2.23 Structure of two high-free-volume substituted polyacetylenes, PTMSP and PMP. The carbon-carbon double bond is completely rigid, and depending on the size of the substituents, rotation around the carbon-carbon single bond can be very restricted also. The result is very stiff-backboned, rigid polymer chains which pack very poorly, leading to unusually high fractional free volumes...

Properties for several TFE/PDD copolymers and PTMSP are compared in Table IV. Density and glass transition temperatures for the TFE/PDD copolymers were obtained from Buck and Resnick (44), and the density and glass transition temperature for PTMSP are from the study of Nakagawa et al.(l). Among the fluoropolymers in this table, PTFE homopolymer exhibits 5ie lowest glass transition temperature, the lowest oxygen permeability coefficient, and the lowest fractional free volume. In the polymers in Table IV, the PALS results suggests a bimodal distribution of free... 

Two of these are under extensive investigation and are currently being studied for gas separation on a pilot scale. These are DuPonfs 2,2-bistrifluoromethyl-4,5-difluoro-l,3-dioxole/tetrafluorethylene copolymer (Teflon AF 2400 ) and poly(4-methyl-2-pentyne) (PMP). All three polymers, PTMSP, PMP and Teflon AF2400, are glassy with glass transition above 230°C and have a very high fractional free volume (FFV). Figure 7.4 shows the chemical structure and fractional free volume of these three polymers. 

Fig. 7.4 Chemical structure and fractional free volume of PTMSP, PMP and Teflon AF2400.

Figure 7 shows the effect of PTBA content on Ch (obtained from CO2 sorption) and oxygen permeability coefficient at 30 C. As expected, both and Oj I rmeability decrease monotonically upon increasing Ae concentration of PTBA since PTBA has a lower fractional free volume than PTMSP. 

Another possible approach to indirectly characterize the membrane morphology is based on the investigation of the free volume within the matrix. Density measurements [119,120] and positron annihilation lifetime spectroscopy evaluation [47] are common methods. Typically, the comparison between the theoretical density or free volume (calculated by simple additivity rules) and the experimental one can reveal the presence of a good interfacial morphology or the presence of interface voids or clustering formation. Fig. 7.13 shows the influence of filler content on the morphology of poly(trimethylsilyl propyne) (PTMSP)/Ti02 NCMs in terms of the volumetric fraction of interface voids as calculated from a comparison of the expected and measured membrane density [119],... 

---