Refractory polymers are usually analyzed using a high-temperature GPC system.
However, the high-temperature GPC system is rather expensive and not so easy to
use. Since HFIP
(hexafluoroisopropanol) dissolves refractory polymers at ordinary
temperature, such polymers are preferably analyzed with HFIP eluent without using
high-temperature GPC systems. GPC is a method using the principle that larger
molecular size (three dimensional volume) of the sample elutes faster. In fact,
the actual molecular size of the sample is different according to the solvent
in which the sample is dissolved. In case of polymers with ionic functional groups,
these groups are repelling each other and the apparent molecular size of the polymers
becomes larger. For preventing such ionic interaction, the addition of
CF3COONa (sodium trifluoroacetate) to HFIP is recommended.
For the analysis of polyamides or poly(ethylene terephthalate) (PET), the use
of HFIP eluent containing CF3COONa is also recommended.
(Refer to Polyamide (1) Nylon6 (HFIP-806M))
(Preparation of the eluent)
Since CF3COONa is not easily dissolved in HFIP, care should be taken to
confirm that it has been thoroughly dissolved, otherwise it may damage the
Method for preparing the eluent is as follows:
1) Weigh necessary amount of CF3COONa and dissolve it in HFIP applying
ultrasonic vibration. The bottle should be shaken often to ensure
thorough ultrasonic vibration.
2) Ultrasonic vibration should be applied for the following time: 10mM CF3COONa in HFIP:
60 min. or more, 5mM CF3COONa in HFIP: 40 min.
3) Use transparent bottle so that undissolved CF3COONa can be seen.
4) During the analysis, the eluent bottle should be kept on a hot plate
and the eluent should be stirred using a magnetic stirrer.