Synthesis, Characterization, and Gas Permeation Properties

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Chapter 4
Table 4. Gas Permeability Coefficients (P) of Polymer Membranes at 25 o C
polymer
P (barrer) a
He H2 O2 N2 CO2 CH4
represents a clear manifestation of the dependence of the gas transport properties of
membrane-forming materials upon the modification of two most important subtle
structural features, i.e. interchain spacing and segmental mobility.
In polymeric membranes, the decrement of gas permeability emanating from
the introduction of polar substituents due to the reduced free volume inside the
polymer matrix is a well established concept; 13 on the contrary, the presence of
spherical side groups is known to bring forth the augmentation in gas permeability
owing to the increased excess free volume and/or enhanced local mobility. 14,15 The
t-butylcarbamates of cellulose derivatives (1a–4a) possess both the aforementioned
features and the local mobility of the side groups playing a dominant role resulted in
the permeability enhancement which was quite substantial for cellulose acetate
derivatives, especially for 4a. These results are quite in compliance with the previous
ones describing a two times increase in the P values to arise from the silylation of
ethyl cellulose (DSEt, 2.69), a four to five times enhancement for silylated cellulose
acetate (DSAc, 2.46), and a magnanimous augmentation of more than 30 times to result
from the silylation of cellulose acetate (DSAc, 1.80). 11b,12
PCO2/PN2 PCO2/PCH4
1 47 68 15 4.3 91 9.2 21.2 9.9
1a 57 75 17 4.7 100 10.5 21.2 9.5
2 41 59 13 3.5 80 7.5 22.9 10.7
2a 51 71 15 3.9 89 8.4 22.8 10.6
3 15 12 0.67 0.14 4.6 0.15 32.8 30.7
3a 27 26 3.1 0.66 19 0.83 28.8 22.9
4 8.4 5.7 0.28 0.044 1.7 0.045 38.6 37.8
4a 34 36 5.5 1.3 38 1.97 29.2 19.3
a 1 barrer = 1x10 -10 cm 3 (STP) cm cm -2 s -1 cmHg -1 .
The most worth mentioning of the gas permeation characteristics of this series