Synthesis, Characterization, and Gas Permeation Properties

59
Chapter 2
IR spectrum of 1 (Figure 1) has a broad band characteristic of the residual hydroxy
groups (3600–3200 cm -1 ), which disappeared upon complete perfluoroacylation in
polymers 2a–d. Further evidence was furnished by the presence of the peaks
characteristic of the carbonyl group (1695–1690 cm -1 ) in the IR spectra of
perfluoroalkanoyl derivatives (2a–d). On the other hand, complete substitution could
not be achieved with pentafluorobenzoyl group, as is indicated by the presence of the
broad band for the hydroxy group (3600–3200 cm -1 ) in the IR spectrum of 2e; its
degree of acylation (DSAc) was determined by the elemental analysis and total degree
Table 1. Degree of Substitution and Molecular Weight of Polymers 1 and 2a–e
polymer DStotal a Mn b Mw b Mw/Mn b
1 2.69 47 000 106 000 2.3
2a 3.00 68 000 103 000 1.5
2b 3.00 93 000 117 000 1.3
2c 3.00 96 000 120 000 1.2
2d 3.00 132 000 147 000 1.1
2e 2.92 c 49 000 124 000 2.5
a Determined by FTIR.
of substitution (DStotal) was 2.92. According to SEC data of the polymers (Table 1),
the number-average molecular weight (Mn) of 1 was found to be 47 000 and a regular
increase in the Mn values of perfluoroacylated polymers was observed with the
increase in the bulk of perfluoroacyl group. Moreover, the polydispersity indices
(Mw/Mn) of perfluoroacylated polymers (2a–d) were not quite different from those of 1.
For instance, the Mn and Mw/Mn of 1 were observed to be 47 000 and 2.3, respectively,
while those of 2a were 68 000 and 1.5. These facts rule out the possibility of
polymer chain cleavage in the course of perfluoroacylation.
b Determined by SEC/RALLS (size-exclusion
chromatography/right-angle laser light scattering). c Determined by elemental analysis.
Solubility and Thermal Properties of Polymers. The solubility properties
of ethyl cellulose (1) and 2a–e are summarized in Table 2. 1 is soluble in highly