Abstract
One of the most important properties of hydrophobically functionalized polyelectrolytes (HF-PEs) and their assemblies is their ability to encapsulate hydrophobic/amphiphilic agents and provide release on demand of the entrapped payload. The aim of the present work was to synthesize and study self-organization behavior in aqueous solution of hydrophobically functionalized poly(acrylic acid) (PAA) comprising the ester-type pH labile moiety with various degrees of hydrophobization and side-chain lengths in the absence and presence of appropriate mono- and polyvalent electrolytes (i.e., NaCl or CaCl2). The synthesis and purification of hydrophobically functionalized PAA were performed under mild conditions in order to avoid chemical degradation of the polymers. The modified polyelectrolytes self-assembly in aqueous systems was monitored using diffusion-ordered nuclear magnetic resonance (DOSY NMR). The performed studies, supported by the all-atoms molecular dynamics simulations, revealed a strong dependence of polyelectrolyte self-assembled state on concentration—specific concentration regions with the coexistence of both smaller and larger aggregates were observed (values of hydrodynamic diameter DH around one nanometer and between two to six nanometers, respectively). Our investigations enabled us to gain crucial information about the self-assembly of the hydrophobically functionalized poly(acrylic acid) and opened the possibility of understanding and predicting its performance under various conditions.
Highlights
Due to their unique self-assembly properties, amphiphilic polymers constitute valuable specialty products, yielding nanocarriers for biomedical purposes, engineered surfaces as well as viscosity modifiers for various applications
The HF-poly(acrylic acid) (PAA) product was designed as a multifunctional material comprising both weak electrolyte moieties and alkyl side chains attached to the polymeric backbone via the ester linkage
The mentioned properties are highly desired for any materials designed toward biomedical purposes
Summary
Due to their unique self-assembly properties, amphiphilic polymers constitute valuable specialty products, yielding nanocarriers for biomedical purposes, engineered surfaces as well as viscosity modifiers for various applications. The aggregate morphologies of non-charged copolymers are controlled by thermodynamic equilibrium: a balance between interfacial tension and chain stretching energies [1]. The most important feature of HF-PEs is their ability to self-assemble into a number of stimuli-responsive morphologies, which may undergo phase transitions or perform a release of solubilized/entrapped payload upon minor changes in temperature, pH, ionic strength, or by external physical stimuli (e.g., electric and magnetic fields) [4,5]. For functionalized polymers comprising PE backbone with hydrophobic side groups, the pH-responsivity is connected with protonation/deprotonation of weak or moderate electrolyte groups as well as hydrolysis of labile bonds between backbone and side chains. The reversible stimuli-responsive nature of HF-PEs in their aqueous solutions is associated with the moderation of hydrogen bonds, e.g., via the introduction of appropriate electrolyte (the influence of ionic strength on hydrogen ions activity) as well as pH or temperature changes
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