Synthesis, Characterization, and Gas Permeation Properties

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almost same pattern of three-step weight loss commencing at approximately 200 ºC,
300 ºC, and 350 ºC, respectively, whereas a two-step weight loss was exhibited by the
starting cellulosic (1). For 2a–f, the first stage of decomposition should correspond
to the cleavage of peripheral t-butoxycarbonyl (t-Boc) groups as t-butyl moieties are
thermally labile (above 180 ºC) and are known to undergo the elimination of
isobutene. 9
Figure 3. TGA curves of polymers 1 and 2a–f (in air, heating rate 10 ºC min -1 ).
The glass transition temperatures (Tg) of polymers (1 and 2a–f) were
determined by the differential scanning calorimetric (DSC) analysis under nitrogen
(Figure 4). The incorporation of t-Boc protected amino acid pendants was observed
to accompany an increase in the glass transition temperature (Tg) of polymers; for
instance, the Tg of 1 was 3.9 ºC whereas those for 2a–f were 35.1–43.3 ºC, respectively
(Table 3). The variation in the glass transition temperature of the polymeric materials
is dramatically affected by the nature of side chains and the increased polarity entails
enhanced Tg values and vice versa. On the other hand, the bulk and shape of the
substituents are also of vital significance and the presence of spherical bulky