## 3 Results and Discussion
A comparison of the SEM results for the CCC-2 samples (Figure 5f) with those previously described (Figure 5a-d) showed the formation of a matrix with a fine cellular structure. This can be explained by ionic cross-linking during the neutralization of the polymer solution with TEDMA, just as in the case of the CCC-1. It can be noted that the scatter of cell sizes was greater than that in the CCC-1 samples. Moreover, it was not possible to estimate the molecular weight parameters of the resulting CCC-2 copolymer because it remained on a filter with a pore size of 0.45 \(\upmu\)m during the preparation of the polymer solution for GPC analysis. CCC-2 (\(\sim\)99% of the polymer product in solution) was observed in the filtered aqueous phase. It was not integrated into the matrix nor the low-molecular-weight collagen, with MM \(\sim\)10 kDa and \(\sim\)20 kDa. Figure 4: The contents of nitrogen and collagen in the samples, according to elemental analysis. At the ratio of components in the CCC-3 copolymer, the organic phase was absent after the synthesis, just as in the case of CCC-2. Before adding the sodium hydroxide solution, the aqueous phase, as in the previous examples, consisted of a stable homogeneous solution of a white polymer product without delamination. However, after adding an alkali solution up to a pH of ~7, coagulation of the polymer product was observed with the gel formation (Figure 3b). The resulting gel easily released water; then, it was dried in a vacuum and formed a film made up of a polymer composite. Gelation after PEG addition to the composition can be explained by additional radical processes. Firstly, it can occur due to interactions between PEG and hydroxyl radicals during synthesis, as in the case of collagen. Secondly, it can observed due to the detachment of a hydrogen atom from the hydroxyl group in PEG, according to scheme (1) (Figure 6). Finally, the hydrocarbon portion of the PEG molecule, according to scheme (2) (Figure 6), can form radicals in the PEG macromolecule. Figure 5: SEM images of (**a**) native collagen [10], (**b**) PMMA-CC graft copolymer [10], (**c,d**) CCC-1 graft copolymer, (**e**) CCC-2 graft copolymer, and (**f**) CCC-3 graft copolymer. These radicals were active in all radical transformations in the reaction mixture. They were able to interact with the monomer and form a grafted synthetic fragment, participate in the chain transfer reaction, or in the disproportionation reaction with another active radical, i.e., form additional covalent bonds in the resulting material. Moreover, as noted earlier [22], PEG formed covalent bonds with amino acid fragments of lysine and arginine (Figure 7). In all cases, PEG acted as a neutral hydrophilic component to ensure steric stabilization of the polymer composite [17; 18; 19; 20; 21; 22]. The chemical interactions during the preparation of new materials and the neutralization of the reaction mixture led to gel coagulation. The addition of PEG into the reaction mixture led to a noticeable decrease in the nitrogen content and, accordingly, collagen in the polymer, in comparison to the previously obtained samples. SEM results for the CCC-3 (Figure 5f) samples showed a matrix with a fine cellular structure in comparison to CCC-1 and CCC-2 (Figure 5c-f). This was related to cross-linking chemical reactions in the reaction mixture occurring during the polymer solution neutralization. It can be noted that the morphology of CCC-3 was very similar to CCC-1 in terms of the cellular structure's uniformity. Similarly to the previous cases with cross-linking agents in the synthesis, it was not possible to estimate the molecular weight parameters of the resulting CCC-3 copolymer, because it remained on a filter with a pore size of 0.45 um while the polymer solution was prepared for GPC analysis. The filtered aqueous phase contained CCC-3 and PEG, which were not integrated into the matrix (with the ratio of graft copolymer to PEG being 1:1).