Synthesis, Characterization, and Gas Permeation Properties

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Chapter 3
(partly soluble) and 3a (soluble). Ethyl cellulose is partly soluble in acetone and
switched to being soluble (2a–c) when derivatized with first generation
amide-containing dendrons and turned insoluble (3a–c) upon the incorporation of
second generation dendritic moieties. 1 and 2a–c were soluble in the moderately
polar cyclic ether, THF, while 3a–c were insoluble. The solubility characteristics of 1
in CHCl3 were unchanged upon dendronization, and all of the dendronized derivatives
of ethyl cellulose were soluble in CHCl3. The appreciably good solubility of
G1-derivatized polymers (2a–c) in CHCl3 was exploited for membrane fabrication.
Furthermore, 1 and 2a–c are soluble (2a is almost soluble) in toluene, a less polar
solvent, while the higher polarity of 3a–c due to the presence of nine amide linkages
renders them insoluble. Thus it can be inferred that the dendronized ethyl cellulose
derivatives tend to be soluble in polar protic solvents like methanol, highly polar
aprotic solvents like DMF, and moderately polar halogenated solvents like CHCl3.
Moreover, the solubility window narrows in going from the G1- to G2-derivatized
polymers.
The thermal stability of polymers 1, 2a–c, and 3a–c was examined by
thermogravimetric analysis (TGA) in air (Figure 4). The onset temperatures of
weight loss (T0) of 2a–c and 3a–c were in the ranges of 295–325 ºC and 312–320 ºC,
respectively, while that of 1 was 297 ºC (Table 3) thus indicating no decrement in
Table 3. Thermal Properties of Polymers 1, 2a–c, and 3a–c
polymer T0 a (°C) Tg b (°C)
1 297 132
2a 295 69
2b 317 57
2c 325 53
3a 320 52
3b 312 40
3c 313 28
a T0: Onset temperature of weight loss. Determined from TGA measurement in air.
b Tg: Glass transition temperature. Determined by DSC analysis under nitrogen.