Synthesis, Characterization, and Gas Permeation Properties

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Chapter 4
reported to lead to the decline in the glass transition temperature of the polymers. 11a,12
Figure 8. DSC thermograms of polymers 3, 4, 3a, and 4a (under N2, second
scan).
However, the present series of polymers (1a–4a) is characterized by the presence of
polar carbamate linkages and the expected decrease in Tg resulting from the
substitution of small hydroxy groups by bulkier carbamoyl functionalities is most
probably offset by the polar nature of the carbamate moieties.
Gas Permeation Properties. The permeability coefficients of the membranes
of 1–4 and 1a–4a to various gases measured at 25 °C are shown in Table 4. The gas
permeability coefficients (P) of the carbamate derivatives (1a–4a) were higher than
those of the starting cellulose derivatives, and the most pronounced enhancement was
observed for 4a. In the case of ethyl cellulose derivatives (1a and 2a) there was a
slight increase in gas permeability without any significant change in permselectivity,
e.g., the PCO2 and PCO2/PN2 of 2a were 89 and 22.8, whereas 80 barrers and 22.9 for 2,