Formation of Hydrophobic–Hydrophilic Associates in the N-Vinylpyrrolidone and Vinyl Propyl Ether Copolymer Aqueous Solutions

Abstract

Utilizing turbidimetry data, an examination is conducted on the behavior of solutions containing N-vinylpyrrolidone and vinyl propyl ether copolymer within a temperature range coinciding with the occurrence of a phase transition. The investigation reveals that within specific conditions prevailing in this domain, the emergence of entities denoted as hydrophobic–hydrophilic associates is conceivable. These entities are characterized by the presence of a relatively dense core, upheld by hydrophobic interplays, and they are proficient in effectively dispersing irradiation within the optical spectrum. Encircling this core is a hydrophilic periphery that impedes the formation of insoluble precipitates. The development of such associates transpires when hydrophobic interactions have attained a discernible prominence, although they remain inadequate to counteract the forces that drive the expansion of macromolecular coils. Under these circumstances, the energetically favored course of action entails the constitution of a core for the aforementioned associates, involving discrete segments from diverse macromolecules. Notably, the introduction of an additional constituent (ethanol) to the solution, which selectively mitigates hydrophobic interactions, serves to stabilize the hydrophobic–hydrophilic associations.

Effect of the Formation of Hydrophilic and Hydrophobic–Hydrophilic Associates on the Behavior of Copolymers of N-Vinylpyrrolidone with Methyl Acrylate in Aqueous Solutions

“…The curves presented in Figure 1 and Figure 2 do not meet this criterion. As the temperature increases, they do not reach a plateau, as is characteristic of the curves studied in the cited works [ 46 , 53 ].…”

“…We emphasize that the phase portrait method has been proposed in our works and is still mainly used by our research group [ 46 , 53 ]. In this and our previous work, it is shown that our proposed method allows us to obtain non-trivial information about the nature of phase transitions.…”

“…Thus, the consideration of the phase transition was actually reduced to the consideration of the processes occurring in an isolated macromolecule. However, the results obtained in [ 45 , 46 ] show that this approach does not fully reflect the real processes occurring in polymer solutions during phase transitions.…”

“…Indeed, those interactions (e.g., hydrophilic) that lead to the formation of a globule (i.e., to the formation of an insoluble component) can play the opposite role. Specifically, they can enhance the observed solubility of the polymer when such interactions occur between functional links belonging to different macromolecular tangles, and also when macromolecules of only one type are present in solution [ 46 ]. In this case, the macromolecule is retained in solution precisely because of those interactions that would seem to favor the loss of solubility.…”

“…The aim of this work is to investigate the influence of hydrophobic–hydrophilic associates (HHAs) on phase transitions in solutions of copolymers of N-vinylpyrrolidone with methyl acrylate (NVP-MA), as well as on the formation of their complexes with polyacrylic acid (PAA). In particular, it is proven that the complex formation between the considered copolymers and PAA is influenced not only by the formation of hydrophilic interpolymer associates (HIAs) studied in [ 45 ], but also by the formation of HHAs, the existence of which was proven in [ 46 ].…”