Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

Abstract

The ionization degree, charge density, and conformation of weak polyelectrolytes can be adjusted through adjusting the pH and ionic strength stimuli. Such polymers thus offer a range of reversible interactions, including electrostatic complexation, H-bonding, and hydrophobic interactions, which position weak polyelectrolytes as key nano-units for the design of dynamic systems with precise structures, compositions, and responses to stimuli. The purpose of this review article is to discuss recent examples of nanoarchitectonic systems and applications that use weak polyelectrolytes as smart components. Surface platforms (electrodeposited films, brushes), multilayers (coatings and capsules), processed polyelectrolyte complexes (gels and membranes), and pharmaceutical vectors from both synthetic or natural-type weak polyelectrolytes are discussed. Finally, the increasing significance of block copolymers with weak polyion blocks is discussed with respect to the design of nanovectors by micellization and film/membrane nanopatterning via phase separation.

Influence of Nanoaggregation Routes on the Structure and Thermal Behavior of Multiple-Stimuli-Responsive Micelles from Block Copolymers of Oligo(ethylene glycol) Methacrylate and the Weak Acid [2-(Hydroxyimino)aldehyde]butyl Methacrylate

“…In fact, based on the degree of dissociation α = 0.5, p K a = 11.2–11.3 is estimated for the HIA groups in H 38 - b -G4 75 , whereas HIABMA has an estimated p K a of 7.7–8.4 (see ref and Figure S6). The effective p K a s of protonated polyelectrolyte repeat units can differ, in theory, by as much as 4 units from those of the monomers, although, in practice, differences are of the order of 1–3 units, also depending on experimental parameters, such as the concentration and presence of salts. , Bütün et al found p K a values of 4.9 to 7.3 for the conjugated acid of a series of poly­(2-dialkylaminoethyl methacrylates), that is 2–3 units lower than small-molecule analogues. On the other hand, the effective p K a of 5 of the protonated pyridine units in poly­(2-vinylpyridine) block copolymers with PEO is the same as the p K a of the monomer, whereas Rodrigues et al found, for the 4-vinylpyridinium units, p K a = 4.64 in poly­(4-vinylpyridine) (P4VP) and p K a = 3.36–3.79 in different mPEG- b -P4VP block copolymers.…”

“…This is a useful feature for applications that require responsivity around physiologically relevant pH values. , In an interesting line of investigation, pH-responsive units were revealed by photocleavage of o -nitrobenzyl ester units in PEG-based amphiphilic methacrylates that were therefore capable of multiple thermal micellization. , The pH-sensitivity of a polymer could, in principle, be exploited to obtain polymeric micelles that are stable around physiological pH as an alternative to the standard solvent switch technique. To this end, ionization should occur well above or below pH 7, contrary to most of the functional groups investigated so far . pH-driven self-assembly may produce different micellar structures than block selectivity-driven aggregation, , thereby causing differences in the response to other stimuli (e.g., temperature or light).…”

“…The development of versatile polymerization techniques triggers limitless creativity in the synthesis of macromolecules of diverse chemistry and topology, including multi-responsive copolymers . Potential applications in sensors, electronics, and biomedical fields draw attention toward the properties of polymeric nanoaggregates in connection with other interacting systems through chemical and physical signals. − Self-assembly of surfactants and polymeric amphiphiles mostly relies on the minimization of unfavorable thermodynamic interactions involving molecular segments and solvents. , This driving force provides the basis for solvent displacement (SD), in which assembly is induced by gradually switching from a good solvent to a segment-selective one. However, as more stimuli-responsive copolymers are being synthesized, micellization has been induced by taking advantage of alternative driving forces other than inherent solvophobicity .…”

“… 1 Potential applications in sensors, electronics, and biomedical fields draw attention toward the properties of polymeric nanoaggregates in connection with other interacting systems through chemical and physical signals. 2 − 6 Self-assembly of surfactants and polymeric amphiphiles mostly relies on the minimization of unfavorable thermodynamic interactions involving molecular segments and solvents. 7 , 8 This driving force provides the basis for solvent displacement (SD), in which assembly is induced by gradually switching from a good solvent to a segment-selective one.…”

“…To this end, ionization should occur well above or below pH 7, contrary to most of the functional groups investigated so far. 2 pH-driven self-assembly may produce different micellar structures than block selectivity-driven aggregation, 36 , 37 thereby causing differences in the response to other stimuli (e.g., temperature or light). In recent years, we have obtained a 2-(hydroxyimino)aldehyde butyl methacrylate (HIABMA) monomer, which has a p K a of the oxime group that is at least 3 orders of magnitude higher than that of acrylic and benzoic acids (see herein), provides multiple sites for hydrogen bonding, has potential for metal chelation, and exhibits a wavelength-dependent photochemical behavior (i.e., E / Z oxime isomerism and an unusually chemoselective Norrish–Yang cyclization).…”