Comicellization of Poly(ethylene glycol)-block-poly(acrylic acid) and Poly(4-vinylpyridine) in Ethanol

Micellization of poly(2-vinylpyrridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) block copolymers and their interpolymer complex formation in non-aqueous medium

HYPOTHESIS

The interpolymer complex formation between poly(vinylpyridine)-based polymers with poly(acrylic acid) (PAA), in aqueous or organic medium, is driven by the hydrogen-bonding complexation. Well-defined nanostructures, with specific practical applications, may be obtained by taking advantage of such non-covalent interactions.

EXPERIMENTS

Poly(2-vinylpyridine)-b-poly(cyclohexyl methacrylate) (P2VP-b-PCHMA) and poly(2-vinylpyridine)-b-poly(t-butyl methacrylate)-b-poly(cyclohexyl methacrylate) (P2VP-b-PtBuMA-b-PCHMA) copolymers were synthesized by sequential anionic polymerization. Their micellar characteristics were examined as a function of their molecular characteristics in methylcyclohexane and toluene respectively, as cycloaliphatic and aromatic solvents for the selective solubilization of the PCHMA sequence. The size of interpolymer complexes was determined by DLS, in 1,4 dioxane, and their structural composition was characterized by ¹H NMR.

FINDINGS

The scaling relationship between the molecular composition and the micellar characteristics, such as particle size and aggregation number, could be established for the PCHMA-based copolymers in methylcyclohexane. It was further demonstrated that controlled micellization in 1,4 dioxane, as a non-selective organic solvent, could be achieved by hydrogen bond type interpolymer complex formation between P2VP-b-PCHMA and PAA-b-PCHMA under stoichiometric P2VP/PAA conditions. Finally, the size of the PCHMA-b-PAA/P2VP block copolymer/homopolymer complexes as well as of the PCHMA-b-PAA/PCHMA-b-P2VP block copolymer/block copolymer complexes was correlated with the molecular characteristics of the copolymers.

Nanofibrillar micelles and entrapped vesicles from biodegradable block copolymer/polyelectrolyte complexes in aqueous media

Here we report a viable route to fibrillar micelles and entrapped vesicles in aqueous solutions. Nanofibrillar micelles and entrapped vesicles were prepared from complexes of a biodegradable block copolymer poly(ethylene oxide)-block-poly(lactide) (PEO-b-PLA) and a polyelectrolyte poly(acrylic acid) (PAA) in aqueous media and directly visualized using cryogenic transmission electron microscopy (cryo-TEM). The self-assembly and the morphological changes in the complexes were induced by the addition of PAA/water solution into the PEO-b-PLA in tetrahydrofuran followed by dialysis against water. A variety of morphologies including spherical wormlike and fibrillar micelles, and both unilamellar and entrapped vesicles, were observed, depending on the composition, complementary binding sites of PAA and PEO, and the change in the interfacial energy. Increasing the water content in each [AA]/[EO] ratio led to a morphological transition from spheres to vesicles, displaying both the composition- and dilution-dependent micellar-to-vesicular morphological transitions.

Hydrogen-bonding-induced complexation of polydimethylsiloxane-graft-poly(ethylene oxide) and poly(acrylic acid)-block-polyacrylonitrile micelles in water

Polydimethylsiloxane-graft-poly(ethylene oxide) (PDMS-g-PEO) copolymers form micelles in water with PDMS as the core and PEO as the corona. The introduction of poly(acrylic acid)-block-polyacrylonitrile (PAA-b-PAN) block copolymers in water leads to the formation of micellar complexes due to the hydrogen bonding between carboxyl groups and ether oxygens among the PAA and PEO chains in the corona of the micelles. The effects of pH, molar ratios (r) of PAA/PEO, and the standing time on the directly mixing these two micelles in water have been investigated using laser light scattering (LLS) and transmission electron microscopy (TEM). Our results showed that the complexation between PAA and PEO in the corona was greatly enhanced at a pH below 3.5. For a fixed pH value, the interactions between these two micelles in water were governed by the value of r. At r < ∼0.6, mixing the two micelles in water resulted in a large floccule because the smaller PAA-b-PAN micelles act as physical cross-links, which are absorbed onto one PDMS-g-PEO micelle and simultaneously bonded to PEO chains on the other micelles, forming bridges and causing flocculation. At ∼0.6 < r < ∼1.2, the mixing led to stable micellar complexes with a layer of PAA-b-PAN micelles absorbed onto the initial PDMS-g-PEO micelles. At r > ∼1.2, the resultant micellar complexes first remained stable, but they precipitated from solution after a long time standing.

Glucose-responsive micelles from self-assembly of poly(ethylene glycol)-b-poly(acrylic acid-co-acrylamidophenylboronic acid) and the controlled release of insulin

Poly(ethylene glycol)-block-poly(acrylic acid-co-acrylamidophenylboronic acid) [PEG(114)-b-(PAA(63)-co-PAAPBA(107))] was synthesized by the modification of poly(ethylene glycol)-block-poly(acrylic acid) (PEG(114)-b-PAA(170)) with 3-aminophenylboronic acid (APBA). Glucose-responsive PEG(114)-b-(PAA(63)-co-PAAPBA(107)) self-assembled into core-shell micelles with the hydrophobic core composed of PAAPBA and hydrophilic shell composed of PEG in aqueous solution. The swelling and disaggregating behaviors of micelles responding to glucose were investigated by using light scattering in aqueous solution at pH 7.4. Characterization of insulin-loaded micelles and their drug release in solutions with various glucose concentrations were further studied. The results demonstrated that the drug release rate can be controlled by variation of glucose concentration.

A valid way of quasi-quantificationally controlling the self-assembly of block copolymers in confined space

To mimic nanostructures assembled by biomolecules in organic cells and achieve precise self-assembly of block copolymers, a simple but valid way is introduced to quasi-quantificationally control the aggregation numbers (N(agg)) of polymeric micelles. A three-dimensional and closed microconfinement similar to a cell is constructed by W/O inverse emulsion as the spot for self-assembly of the pH-responsive block copolymer poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG-b-P4VP). The N(agg) values of the resulting polymeric micelles are effectively controlled by tuning the number of polymer chains encapsulated in isolated water pools. Micelles with different N(agg) values are successfully prepared and characterized by atomic force microscopy, transmission electron microscopy, and dynamic light scattering. When the number of polymer chains enclosed in a water pool (N(chain)) is less than the average N(agg) of normal micelles generated in bulk aqueous solution, the resultant aggregates formed in the confined spaces always have lower N(agg) as well as smaller sizes than the normal micelles do, while normal micelles predominantly form when N(chain) > N(agg) (normal micelle).

Complex coacervate core micelles

In this review we present an overview of the literature on the co-assembly of neutral-ionic block, graft, and random copolymers with oppositely charged species in aqueous solution. Oppositely charged species include synthetic (co)polymers of various architectures, biopolymers - such as proteins, enzymes and DNA - multivalent ions, metallic nanoparticles, low molecular weight surfactants, polyelectrolyte block copolymer micelles, metallo-supramolecular polymers, equilibrium polymers, etcetera. The resultant structures are termed complex coacervate core/polyion complex/block ionomer complex/interpolyelectrolyte complex micelles (or vesicles); i.e., in short C3Ms (or C3Vs) and PIC, BIC or IPEC micelles (and vesicles). Formation, structure, dynamics, properties, and function will be discussed. We focus on experimental work; theory and modelling will not be discussed. Recent developments in applications and micelles with heterogeneous coronas are emphasized.

Self-assembly behavior of A-B diblock and C-D random copolymer mixtures in the solution state through mediated hydrogen bonding

We have synthesized poly(methyl methacrylate- b-4-vinylpyridine) (PMMA- b-P4VP) and poly(styrene- r-vinylphenol) (PS- r-PVPh) copolymers by using anionic and free radical polymerizations, respectively. Well-defined micelles through hydrogen bonding have been prepared by mixing PMMA- b-P4VP diblock copolymer and PS- r-PVPh random copolymer in a single solvent. Block copolymers were mixed with random copolymers, with various [N]/[OH] ratios (4/1, 2/1, 1/1, and 1/4) in which "[N]/[OH]" represents the molar ratio of pyridine groups on P4VP to hydroxyl groups on PVPh. The presence distribution of PVPh/P4VP and PVPh/PMMA hydrogen bonding depends on the feeding ratio of PVPh to P4VP. When the PVPh content is lower than that of P4VP, hydrogen bonding occurs only between PVPh and P4VP; with excess PVPh, additional hydrogen bonding between PVPh and PMMA would occur. Furthermore, the effect of the solvent quality on the self-assembly behavior of PMMA- b-P4VP/PS- r-PVPh blends is investigated by considering tetrahydrofuran (THF) and dimethylformamide (DMF) as common solvents. We can mediate the strength of hydrogen bonding in blend systems by adopting different solvents and inducing different morphology transitions.

Pyranine-induced micellization of poly(ethylene glycol)-block-poly(4-vinylpyridine) and pH-triggered release of pyranine from the complex micelles

The pyranine-induced micellization of poly(ethylene glycol)-block-poly(4-vinylpyridine) (PEG114-b-P4VP61) in aqueous solutions and pH-triggered release of pyranine from the complex micelles were studied by dynamic and static light scattering, transmission electron microscopy, 1H NMR spectroscopy, and UV-vis spectroscopy. At pH 2, the ionized pyranine can ionically cross-link the protonated P4VP block and result in well-defined spherical complex micelles with a P4VP/pyranine core surrounded by a PEG corona. The ratio of pyranine to pyridyl units can influence the structure and the properties of the resultant complex micelles. The complex micelles are stable upon dilution and heating but are sensitive to pH changes. pH-triggered release of the incorporated pyranine from the complex micelles demonstrates that the release behavior is pH-tunable and displays good controlled-release characteristics at pH approximately 4.

Interpolymer Complexes Based on the Core/Shell Micelles. Interaction of Polystyrene-block-poly(methacrylic acid) Micelles with Linear Poly(2-vinylpyridine) in 1,4-Dioxane Water Mixtures and in Aqueous Media

The size and structural changes of nanoparticles formed after the addition of poly(2-vinylpyridine), PVP, to block copolymer micelles of polystyrene-block-poly(methacrylic acid), PS-PMA, were studied by light scattering and atomic force microscopy. Due to the strong hydrogen bonding between PVP and PMA segments, complex structures based on the core/shell micelles form in mixed selective solvents. As proven by a combination of light scattering and atomic force microscopy, individual PS-PMA micelles are "glued" together by PVP chains. The dialysis against solvents with a high content of water results in transient increase in polydispersity and turbidity of originally clear solutions. However, the precipitated polymer material dissolves in basic buffers and stable soluble nanoparticles reform in aqueous media. The behavior of their solutions was studied in a broad pH range by light scattering, atomic force microscopy and capillary zone electrophoresis.

Thermoresponsiveness of hybrid micelles from poly(ethylene glycol)-block-poly(4-vinylpyridium) cations and SO4(2-) anions in aqueous solutions

The SO4(2-)-induced micellization of poly(ethylene glycol)-block-poly(4-vinylpyridium) (PEG110-b-P(4-VPH+)35) and the thermoresponsiveness of these hybrid micelles are studied by dynamic and static light scattering. When the concentration of H2SO4 is high enough, PEG110-b-P(4-VPH+)35 forms stable hybrid micelles with an ionic core of P(4-VPH+)35/SO4(2-) and a PEG corona at 25 degrees C. The formation of the hybrid micelles is reversible. A thermodynamic equilibrium exists between the hybrid micelles and PEG110-b-P(4-VPH+)35 unimers. The shifts of the equilibrium are mainly attributed to the variation of the electrostatic energy and entropic energy of the system. Therefore, the temperature can determine the states of the equilibrium, which means that the dissociation or the formation of the hybrid micelles can be triggered by just varying the temperature.

Formation of hybrid micelles between poly(ethylene glycol)-block-poly(4-vinylpyridinium) cations and sulfate anions in an aqueous milieu

The SO-induced micellization of poly(ethylene glycol)--poly(4-vinylpyridinium)(PEG-b-P(4-VPH)) in aqueous solution is studied by dynamic and static light scattering, and transmission electron microscopy. The SO anions can act as cross-linkers of the P(4-VPH) blocks through the electrostatic attraction between 4-VPH and SO to induce the micellization of PEG--P(4-VPH). The resultant hybrid micelles are spherical and consist of an ion-complex core of P(4-VPH)/SO and a water-soluble PEG corona and present a density gradient between the core and corona and the core has a higher density. The SO concentrations can affect the structure of the core-corona hybrid micelles. The low SO conentration leads to a loose core while the high SO concentration leads to a compact core.