Synthesis, Characterization, and Gas Permeation Properties

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Chapter5
in Table 1. The molecular weight determination of hydroxypropyl cellulose (1; MS,
4.61) and its amino acid esters (2a–f) was carried out by making use of LiBr solution
(0.01 M) in DMF as eluent because of good solubility of these polymeric materials in
DMF. The esterification of HPC involving the substitution of small hydroxy protons
with bulky organic moieties accompanied an increase in the molecular weight of the
polymers; e.g., the Mn of 1 was observed to be 71 000 while those for 2a–f were 154
000–216 000, respectively. Moreover, the polydispersity indices (Mw/Mn) of the
amino acid-functionalized polymers (2a–f) were not quite different from those of 1;
for instance, the Mw/Mn of 1 and 2a–f were 4.3 and 4.2–5.7, respectively, thus ruling
out the possibility of polymer chain cleavage under the mild reaction conditions
employed for esterification.
Table 1. Degree of Esterification (DSEst) and Molecular Weight of Polymers 1
and 2a–f
polymer DSEst a Mn b Mw b Mw/Mn b
1 0.0 71 000 310 000 4.3
2a 3.0 154 000 883 000 5.7
2b 3.0 172 000 891 000 5.2
2c 1.1 216 000 905 000 4.2
2d 1.0 180 000 865 000 4.8
2e 1.7 183 000 871 000 4.7
2f 3.0 194 000 937 000 4.8
a Determined by 1 H NMR. b Determined by GPC (0.01 M LiBr in DMF as eluent).
Solubility and Thermal Properties of Polymers. The solubility
characteristics of hydroxypropyl cellulose (1) and its amino acid esters (2a–f) are
shown in Table 2. 1 is soluble in polar protic solvents such as methanol, highly polar
aprotic solvents like DMF and DMSO, and moderately polar acetone. The same
tendency was retained upon the incorporation of aminoalkanoyl substituents which can