Synthesis, Characterization, and Gas Permeation Properties

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Chapter 4
Figure 2. 1 H NMR spectra of 3, 3a, and 4a.
Labels: a, terminal methyl protons of cellulose acetate; a′, terminal methyl
protons derived from cellulose acetate; b′, terminal methyl protons of the carbamoyl
moiety.
indicating the presence of 0.31 and 0.50 hydroxy groups per anhydroglucose unit.
The DSAc of 3 was determined in a similar way whereas that for 4 was provided by the
manufacturer. The 1 H NMR spectra of the starting polymers (1–3) and their
carbamate derivatives (1a–4a) are shown in Figures 1 and 2. Although the 1 H NMR
spectra of the derivatized polymers provided a clear indication of the incorporation of
t-buytlcarbamoyl group, the calculation of the exact degree of carbamoylation (DSCarb)
for 1a and 2a could not be carried out due to the overlapping of the peaks arising from
the methyl protons of the ethyl group of ethyl cellulose and those of the carbamate
moiety. Further evidence was furnished by the presence of the peaks characteristic of
the C=O stretching (1742–1733 cm -1 ) and NH-bending (1524–1499 cm -1 ) of the
carbamate, in the IR spectra of the resulting polymers (1a–4a). The IR spectra of 1–4
(Figures 3 and 4) displayed a broad band attributable to the residual hydroxy groups
(3600–3200 cm -1 ), which did not disappear completely upon carbamate formation as
the NH bond of the carbamoyl moiety also absorbs IR radiation in the same