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impurities are separated from the polymer solution prior to analysis. An instrument
from Postnova Analytics (Munich, Germany) was used for the AF
4
experiments.
Refractive index (RI), UV, Multi-Angle Laser Light Scattering (MALLS) and an
Evaporative Light Scattering Detector (ELSD) were used as detectors.
2.3.3. TG/DTG and IR analyses
Thermogravimetric measurements were performed with a DTA 220 balance from
Seiko Instruments (USA). IR spectra were recorded on a Vector 22 instrument,
made by Bruker (Karlsruhe, Germany), or on a Nexus 550 instrument made by
Nicolet (Offenbach, Germany).
2.4. Labelling of surface functional groups
2.4.1. Derivatization of OH groups
Samples with surface OH groups were exposed to trifluoroacetic anhydride
(TFAA) vapour for 10-15 min in order to react as follows:
Afterwards these samples were degassed at a pressure of 10
-5
Pa to remove the
produced trifluoroacetic acid [35, 36]. The derivatization of OH groups proved to
be highly selective (ca. 90% [36]). F1s peak intensities in the XPS spectra as well
as >C=O (1785 cm
-1
) and CF
3
(1223 cm
-1
) stretching vibrations were used to
evaluate the number of surface OH groups [35].
2.4.2. Derivatization of NH
2
groups
Primary amino groups react with pentafluorobenzaldehyde (PFBA) or trifluoro-
methyl benzaldehyde (TFBA) by formation of a Schiff's base:
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