Interpolyelectrolyte complexes (IPECs) are typically formed when two polyelectrolytes of opposite charge are mixed together in solution. We present an overview of different strategies for the preparation of micellar IPECs, i.e., structures where such IPEC domains form the core or the shell of micelles. In addition, vesicular architectures are considered, where the IPEC domain forms a membrane layer. One intriguing feature of IPECs is that their formation can be directed, their stability towards changes in pH or ionic strength can (to a certain extent) be predicted, and their size can be controlled. Especially the use of ionic/non-ionic block copolymers offers unique potential for the preparation of well-defined and sophisticated nanostructured materials. We also discuss possible applications, especially in the field of life sciences, including biocompatibility, the controlled uptake/release of guest substances, the immobilization of enzymes, or the controlled formation of inorganic/organic hybrid materials.

Amphiphilic diblock copolymers, poly(n-butyl acrylate)-block-poly(acrylic acid) (PnBA-PAA), with narrow molecular weight distribution (PDI ≤ 1.07) were prepared by atom transfer radical polymerization (ATRP) of n-butyl acrylate and tert-butyl acrylate (tBA), followed by selective acidolysis of the PtBA block. These polymers possess a soft PnBA hydrophobic block with a constant chain length of 90−100 monomer units and pH- and ionic strength-sensitive hydrophilic PAA block with DPPAA = 33−300 AA monomer units. They were expected to form stimuli-responsive micelles. The block copolymers with DPPAA ≥ 100 are directly soluble in water at pH > 4.7. Pyrene steady-state fluorescence spectroscopy and fluorescence correlation spectroscopy (FCS) studies indicate the existence of a very low critical micelle concentration (cmc ∼ 10-8 mol/L). The number-average hydrodynamic radii of the micelles, as determined by FCS, range from 28 to 55 nm, depending on the PAA block length. FCS data indicate that micellar sizes significantly decrease upon dilution for salt-free systems. This is attributed to a dynamic, but kinetically controlled, behavior of these self-assembled nanostructures. In saline solutions the micellar sizes remain constant above the “apparent” cmc (cmc*), which is attributed to slower dynamics of unimer exchange between micelles.

This work examines the fabrication regime and the properties of microgel and microgel/enzyme thin films adsorbed onto conductive substrates (graphite or gold). The films were formed via two sequential steps: the adsorption of a temperature- and pH-sensitive microgel synthesized by precipitation copolymerization of N-isopropylacrylamide (NIPAM) and 3-(N,N-dimethylamino)propylmethacrylamide (DMAPMA) (poly(NIPAM-co-DMAPMA) at the pH-condition corresponding to its noncharged state (first step of adsorption), followed by the enzyme, tyrosinase, adsorption at the pH-condition when the microgel and the enzyme are oppositely charged (second step of adsorption). The stimuli-sensitive properties of poly(NIPAM-co-DMAPMA) microgel were characterized by potentiometric titration and dynamic light scattering (DLS) in solution as well as by atomic force microscopy (AFM) and quartz crystal microbalance with dissipation monitoring (QCM-D) at solid interface. Enhanced deposition of poly(NIPAM-co-DMAPMA) microgel particles was shown at elevated temperatures exceeding the volume phase transition temperature (VPTT). The subsequent electrostatic interaction of the poly(NIPAM-co-DMAPMA) microgel matrix with tyrosinase was examined at different adsorption regimes. A considerable increase in the amount of the adsorbed enzyme was detected when the microgel film is first brought into a collapsed state but then was allowed to interact with the enzyme at T < VPTT. Spongelike approach to enzyme adsorption was applied for modification of screen-printed graphite electrodes by poly(NIPAM-co-DMAPMA)/tyrosinase films and the resultant biosensors for phenol were tested amperometrically. By temperature-induced stimulating both (i) poly(NIPAM-co-DMAPMA) microgel adsorption at T > VPTT and (ii) following spongelike tyrosinase loading at T < VPTT, we can achieve more than 3.5-fold increase in biosensor sensitivity for phenol assay. Thus, a very simple, novel, and fast strategy for physical entrapment of biomolecules by the polymeric matrix was proposed and tested. Being based on this unique stimuli-sensitive behavior of the microgel, this stimulated spongelike adsorption provides polymer films comprising concentrated biomaterial.

Dynamic core-shell-shell-corona micelles are formed between two oppositely charged block copolymer systems. Preformed polybutadiene-block-poly(N-methyl-2-vinylpyridinium)-block-poly(methacrylic acid) (PB-P2VPq-PMAA) block terpolymer micelles with a soft polybutadiene core, an interpolyelectrolyte complex (IPEC) shell made out of poly(N-methyl-2-vinylpyridinium) and poly(methacrylic acid), and a negatively charged PMAA corona were mixed in different ratios at high pH with positively charged poly(N-methyl-2-vinylpyridinium)-block-poly(ethylene oxide) (P2VPq-PEO) diblock copolymers. Under these conditions, mixing results in the formation of a second IPEC shell onto the PB-P2VPq-PMAA precursor micelles, surrounded by a PEO corona. The resulting multicompartmented IPECs exhibit dynamic behavior, highlighted by a structural relaxation within a period of 10 days, investigated by dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and scanning force microscopy (SFM). After a short mixing time of 1 h, the IPECs exhibit a star-shaped structure, whereas after 10 days, spherical core-shell-shell-corona objects could be observed. To further increase complexity and versatility of the presented systems, the in situ formation of gold nanoparticles (Au NPs) in both the precursor micelles and the equilibrated IPEC was tested. For the PB-P2VPq-PMAA micelles, NP formation resulted in narrowly distributed Au NPs located within the PMAA shell, whereas for the core-shell-shell-corona IPEC, the Au NPs were confined within the IPEC shell and shielded from the outside through the PEO corona.

We report on interpolyelectrolyte complexes (IPECs) formed by micelles of ionic amphiphilic diblock copolymers with polyisobutylene (PIB) and poly(sodium methacrylate) (PMANa) blocks interacting with quaternized poly(4-vinylpyridine) (P4VPQ). The interpolyelectrolyte complexation was followed by turbidimetry and small angle neutron scattering (SANS). The data obtained by means of a combination of SANS, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) provide evidence on the core-shell-corona structure of the complex species with the shell assembled from fragments of electrostatically bound PMANa and quaternized P4VPQ fragments, original PIBx-b-PMAAy micelles apparently playing a lyophilizing part. The complex formation is followed by potentiometric titration as well. This process is initially kinetically controlled. In the second step larger aggregates rearrange in favor of smaller complexes with core-shell-corona structure, which are thermodynamically more stable. An increase in ionic strength of the solution results in dissociation of the complex species as proven by SANS and analytical ultracentrifugation (AUC). This process begins at the certain threshold ionic strength and proceeds via a salt-induced gradual release of chains of the cationic polyectrolyte from the complex species.

The interaction of polyisobutylene-block-poly(sodium methacrylate) diblock copolymer micelles with a strong cationic polyelectrolyte, poly(N-ethyl-4-vinylpyridinium bromide), in alkaline media was examined by means of turbidimetry, analytical ultracentrifugation, and fluorescence spectroscopy. It was shown that the diblock copolymer micelles and the cationic polyelectrolyte, taken at charge ratios Z = [+]/[−] not exceeding a certain critical value Z M < 1, form peculiar water-soluble micellar complex species, each containing a two-phase hydrophobic nucleus and a hydrophilic corona. The nucleus consists of a polyisobutylene core and a shell assembled from the fragments of the water-insoluble interpolyelectrolyte complex. The corona is formed by the excess fragments of poly(sodium methacrylate) blocks not involved in the complexation with poly(N-ethyl-4-vinylpyridinium bromide).

Poly(tert‐butoxycarbonylaminomethylacrylate) (PtBAMA), a derivative of polydehydroalanine (PDha), is synthesized using free radical polymerization (FRP) and nitroxide mediated polymerization (NMP). Due to the presence of orthogonal protective groups, the resulting polymers can be selectively deprotected to yield either a polyanion (poly(tert‐butoxycarbonylaminoacrylic acid), PtBAA) or a polycation (poly(aminomethylacrylate), PAMA). Deprotection of both the amino‐ and the carboxyl‐functionality in a sequential manner leads to the potential polyzwitterion polydehydroalanine (PDha). The pH‐dependent solution behavior of PtBAA, PAMA, and PDha are examined in aqueous solution by potentiometric and turbidimetric titrations as well as ζ‐potential measurements.

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