Synthesis, Characterization, and Gas Permeation Properties

96
Dendronization of Ethyl Cellulose
These facts rule out the possibility of polymer chain cleavage in the course of
esterification. However, observed Mn values were twice those of the theoretical ones
for G1-functionalized polymers (2a–c) which might have resulted either due to the
aggregation of dendronized polymers in DMF or relatively nonpolar and quite
different morphological nature of the polystyrene standards which have been used to
construct the calibration curve employed for the estimation of the molecular weight.
With G2-derivatized polymers (3a–c), very broad GPC elution curves and
irreproducibility of the results did not allow the correct molecular weight
determination. This might be due to the low solubility (Table 2) and/or anomalous
elution, which is known to occur in very large polymers or aggregated systems. 22
Solubility and Thermal Properties of Polymers. The solubility properties
of ethyl cellulose (1) and its G1- and G2-functionalized (2a–c and 3a–c) derivatives
are summarized in Table 2. 1 is soluble in polar protic solvents such as methanol and
the same tendency was retained after dendronization. The solubility behavior of
dendronized polymers in polar aprotic solvents exhibited several variations depending
on the polarity of the solvent and the length of the peripheral alkyl groups of dendritic
moieties. For instance, 1, 2a–c, and 3a were soluble in DMF whereas 3b and 3c were
almost soluble (can not be described as completely soluble); on the other hand, 1 is
soluble in DMSO but all of the dendronized derivatives were insoluble except 2a
Table 2. Solubility a of Polymers 1, 2a–c, and 3a–c
polymer 1 2a 2b 2c 3a 3b 3c
methanol + + + + + + +
DMF + + + + + ± ±
DMSO + ± – – + – –
acetone ± + + + – – –
THF + + + + – – ±
CHCl3 + + + + + + +
toluene + ± + + – – –
hexane – – – – – – –
a Symbols: +, soluble; ±, partly soluble; –, insoluble.