## 3 Results and Discussion
### FTIR Measurements  
To identify the radiochemical transformations of polymers, FTIR spectra of the systems in dry state were recorded. In Figure 3, FTIR spectra for **PAA** before and after irradiation are plotted. The absorption bands for the non-irradiated polymer are ascribed as follows: OH stretching--a broad band around 3300 cm\({}^{-1}\), CH and CH\({}_{2}\) stretching at 2960-2880 cm\({}^{-1}\), C = O stretching--an intense band at 1696 cm\({}^{-1}\), CH\({}_{2}\) bending at 1450 cm\({}^{-1}\), C-O-H bending at 1418 cm\({}^{-1}\), C-O stretching at 1236 and 1164 cm\({}^{-1}\). The two vibrations for C-O stretching appeared due to involvement of some acid groups in the formation of hydrogen bonds, which lowered the stretching frequency for such groups. For the same reason, the prominent band corresponding to C = O stretching had a lower wavenumber than 1710-1700 cm\({}^{-1}\) which was usually obtained for carboxylic acids. The lack of any peak around 1565-1542 cm\({}^{-1}\) that corresponded to asymmetric stretching of COO\({}^{-}\) proved that almost all functional groups of **PAA** existed in the nonionized form.  
After irradiation, some changes in the FTIR spectra occurred. Thus, OH stretching became less visible and eventually disappeared, and the shape of the two peaks assigned to C-O stretching vibrations in carboxyl group changed. Thus, due to a certain degree of decarboxylation \(\gamma\)-radiation induced, both peaks located on 1236 and 1164 cm\({}^{-1}\) weakened, which indicated that carboxyl groups were still present and engaged in hydrogen bonding even after irradiation. Nevertheless, a part of the functional groups attached to the monomer units were destroyed or involved in the crosslinks formed during irradiation. As a consequence, ketone and ester groups could appear, although they were difficult to identify when carboxyl groups were also present. Another important change could be observed in the region of C-O-H bending (1418 cm\({}^{-1}\)). This peak also became less visible due to an easy subtraction of hydrogen.  
The two copolymers, **PAH18** and **PAH9**, have very similar FTIR spectra. Thus, in Figure 4, for better clarity, only the un-crosslinked **PAH18** spectrum is presented, together with the spectra of both copolymers after irradiation at specified absorption doses. For un-crosslinked copolymers, the IR spectra were very much like the IR spectrum of **PAA**: broad band around 3300 for OH stretching, overlapping it with CH stretching at 2960 cm\({}^{-1}\), strong peak at 1705 cm\({}^{-1}\) (C = O stretching), CH\({}_{2}\) and OH bending at 1454 and 1413 cm\({}^{-1}\), respectively, and C-O stretching at 1260 and 1169 cm\({}^{-1}\). The two new bands at 1100 and 1020 cm\({}^{-1}\) could be assigned to the stretching vibrations associated to C-O bonds in ester and alcohol moieties.  
Figure 3: FTIR spectra for poly(acrylic acid) (**PAA**) before and after irradiation.  
After irradiation of **PAH18**, the peaks located at 1100 and 1020 cm\({}^{-1}\) could no longer be observed, which proved that large fractions of these side functional groups totally transformed/disappeared under the action of \(\gamma\)-rays. For copolymer **PAH9**, that had more HEMA units in the backbone, the peaks corresponding to ester and alcohol bonds were still present. The same conclusion could be drawn for the peak corresponding to OH bending (1413 cm\({}^{-1}\)).