## 4 Conclusions  
The role of cationic modification of cotton fabric with P(VBC-co-VBCTEAMx) polymers during the dyeing process is explored in the present work at the molecular scale. Several spectroscopic techniques were applied, and detailed information related to the interaction of the reactive dye molecules with the cationic polymer modifiers at the molecular level was acquired. Two differently structured reactive dyes were used: (a) Novacron Ruby S-3B possessing five negatively charged sulfonate/sulfate groups and two possible reactive sites with cellulose (vinyl sulfone and chloro-triazine) and (b) Remazol Brilliant Blue R possessing two negatively charged sulfonate/sulfate groups and one possible reactive site with cellulose (vinyl sulfone). Regarding the number of available cationic sites in the modifier, its effect was investigated by using the two extreme values for the cationic content x that secure solubility in water (x = 53 and x = 100). Binary dye-polymer aqueous solutions (when a polymer is in large excess), as well as precipitates (at stoichiometric charge ratio), were studied. UV-Vis spectroscopy indicates dye-polymer interactions in the aqueous solutions of the binary systems by measurable small redshifts in the dye absorption bands. In addition, noticeable blueshifts in the dye bands are observed in analogous fluorescence experiments. In the precipitates of the binary systems, experimental evidence for the coupling of sulfonate/sulfate anions with N\({}^{+}\) is provided by ATR-FTIR and XPS spectroscopy. Furthermore, XPS enabled the extraction of the ratio of the number of VBCTEAM units per dye molecule for each of the binary systems studied. Finally, for the modified dyed fabrics, XPS indicates a considerable portion of sulfate and chloro-triazine dye reactive sites, which indicates that the main mechanism of dye molecules attached to the fiber is through dye-modifier electrostatic interactions. As a result, the cationic modifier containing both VBC and VBCTEAM units acts as a connecting linkage of cellulose and dye molecules. Under  
Figure 14: Fitted XPS spectra for the sulfur orbital 2p of pristine Novacron Ruby S-3B and untreated dyed cotton. Blue peaks denote the SO3\({}^{-}\) doublet (corresponding to 2p\({}_{3}\)/2/2p\({}_{1/2}\) lines solid/dashed lines respectively) while pink curves denote the contribution of the SO4\({}^{-}\) doublet (absent in the untreated dyed cotton). Inset demonstrates the similarity of the spectra between pristine Novacron Ruby S-3B and the modified dyed cotton. standing the different interactions involved in the proposed dying process may assist in the upscaling and optimization of the process as well as give insight into alternative structures of polymer chains that offer additional properties to the modified cotton fabrics. Furthermore, it triggers additional research required to justify the problem of dye release during fabric washing while exploitation of applying the use of the proposed modifiers with other non-reactive dyes may be also reasonable. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13095530/s1](https://www.mdpi.com/article/10.3390/app13095530/s1)]([https://www.mdpi.com/article/10.3390/app13095530/s1](https://www.mdpi.com/article/10.3390/app13095530/s1)), Figure S1: \"Aqueous solutions of (a) polymer modifier PVBCTEAM, (b) Remazol Brilliant Blue R/PVBCTEAM, (c) Novacron Ruby/PVBCTEAM and (d) Remazol Blue/PVBCTEAM binary mixture at stoichiometric charge ratio after 24 h; clearly visible is the phase separation of the insoluble precipitate. Similar result has been observed after 24 h for Novacron Ruby also.\"; Figure S2: \"XPS spectra in the N\({}_{18}\) spectral region of the precipitates of all binary system at stoichiometric charge ratios.