Synthesis, Characterization, and Gas Permeation Properties

Perfluoroacylation of Ethyl Cellulose
corresponding hydrocarbon polymers. 10b It is worth mentioning that the
perfluoroalkanoylation resulted in an enhancement in the FFV values of polymer
membranes (2a–d) regardless of the simultaneous increase in their density as
compared to the starting material (1). For instance, 2c was observed to possess the
highest fractional free volume (FFV is 0.197), in spite of its quite high density (ρ is
1.194) among all of the perfluoroacylated derivatives of 1, which probably indicates
the formation of relatively sparse structures due to the incorporation of
fluorine-containing moieties. Similar tendencies have been reported in F-containing
polycarbonates. 12 Furthermore, it is a general trend that the bulky substituents
sterically obstruct intersegmental packing, 9 and in the case of F-containing polymers
chain packing is further restrained by the intermolecular repulsive forces resulting
from the presence of fluorine atoms having high electron density.
Table 5. Physical Properties of Polymers 1 and 2a–e
polymer υw a (cm 3 /mol) ρ b (g/cm 3 ) FFV c
1 135.8 1.099 0.182
2a 145.0 1.155 0.185
2b 149.6 1.178 0.189
2c 154.2 1.194 0.197
2d 172.5 1.298 0.191
2e 150.9 1.206 0.161
a υw: van der Waals volume. b ρ: density. Determined by hydrostatic weighing. c
FFV: fractional free volume. Estimated from membrane density.
Gas Permeation Properties. The permeability coefficients of the
membranes of polymers 1 and 2a–e to various gases measured at 25 °C are listed in
Table 6, and their plot versus kinetic diameter of gases is shown in Figure 5. The gas
permeability coefficients (P) of the perfluoroacylated derivatives (except 2e) were
higher than that of 1, and approximately obey the following order: 2c > 2b ≈ 2d > 2a >
1 > 2e, which is in accordance with the FFV of the polymer membranes. The order
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