Supramolecular assemblies of amphiphilic PMMA-block-PAA stars in aqueous solutions

Reconfiguration of Langmuir Monolayers of Thermo-Responsive Branched Ionic Polymers with LCST Transition

Thermo-responsive ionic polymers have the ability to form adaptive and switchable morphologies, which may offer enhanced control in energy storage and catalytic applications. Current thermo-responsive polymers are composed of covalently attached thermo-responsive moieties, restricting their mobility and global dynamic response. Here, we report the synthesis and assembly at the water-air interface of symmetric and asymmetric amphiphilic thermo-responsive branched polymers with weakly ionically bound arms of amine-terminated poly(N-isopropylacrylamide) (PNIPAM) macro-cations. As we observed, symmetric branched polymers formed multimolecular nanosized micellar assemblies, whereas corresponding asymmetric polymers formed large, interconnected worm-like aggregates. Dramatic changes in localized and large-scale chemical composition confirmed the reversible adsorption and desorption of the mobile PNIPAM macro-cations below and above the low critical solution temperature (LCST) and their non-uniform redistribution within polymer monolayer. Increasing the temperature above LCST led to the formation of large interconnected micellar aggregates because of the micelle-centered aggregation of the hydrophobized PNIPAM macro-cationic terminal chains in the aqueous subphase. Overall, this work provides insights into the dynamic nature of the chemical composition of branched ionic polymers with weakly ionically bound thermo-responsive terminal chains and its effect on both morphology and local/surface chemistry of monolayers at LCST transition.

Self-Organization in Dilute Aqueous Solutions of Thermoresponsive Star-Shaped Six-Arm Poly-2-Alkyl-2-Oxazines and Poly-2-Alkyl-2-Oxazolines

The behavior of star-shaped six-arm poly-2-alkyl-2-oxazines and poly-2-alkyl-2-oxazolines in aqueous solutions on heating was studied by light scattering, turbidimetry and microcalorimetry. The core of stars was hexaaza [2₆] orthoparacyclophane and the arms were poly-2-ethyl-2-oxazine, poly-2-isopropyl-2-oxazine, poly-2-ethyl-2-oxazoline, and poly-2-isopropyl-2-oxazoline. The arm structure affects the properties of polymers already at low temperatures. Molecules and aggregates were present in solutions of poly-2-alkyl-2-oxazines, while aggregates of two types were observed in the case of poly-2-alkyl-2-oxazolines. On heating below the phase separation temperature, the characteristics of the investigated solutions did not depend practically on temperature. An increase in the dehydration degree of poly-2-alkyl-2-oxazines and poly-2-alkyl-2-oxazolines led to the formation of intermolecular hydrogen bonds, and aggregation was the dominant process near the phase separation temperature. It was shown that the characteristics of the phase transition in solutions of the studied polymer stars are determined primarily by the arm structure, while the influence of the molar mass is not so significant. In comparison with literature data, the role of the hydrophobic core structure in the formation of the properties of star-shaped polymers was analyzed.

Smart, Naturally-Derived Macromolecules for Controlled Drug Release

A series of troxerutin-based macromolecules with ten poly(acrylic acid) (PAA) or poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) homopolymer side chains were synthesized by a supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) approach. The prepared precisely-defined structures with low dispersity (M_w/M_n < 1.09 for PAA-based, and M_w/M_n < 1.71 for PDMAEMA-based macromolecules) exhibited pH-responsive behavior depending on the length of the polymer grafts. The properties of the received polyelectrolytes were investigated by dynamic light scattering (DLS) measurement to determine the hydrodynamic diameter and zeta potential upon pH changes. Additionally, PDMAEMA-based polymers showed thermoresponsive properties and exhibited phase transfer at a lower critical solution temperature (LCST). Thanks to polyelectrolyte characteristics, the prepared polymers were investigated as smart materials for controlled release of quercetin. The influence of the length of the polymer grafts for the quercetin release profile was examined by UV–VIS spectroscopy. The results suggest the strong correlation between the length of the polymer chains and the efficiency of active substance release, thus, the adjustment of the composition of the macromolecules characterized by branched architecture can precisely control the properties of smart delivery systems.

Miniemulsion RAFT Copolymerization of MMA with Acrylic Acid and Methacrylic Acid and Bioconjugation with BSA

Polymerization through reversible addition-fragmentation chain-transfer (RAFT) polymerization has been extensively employed for the production of polymers with controlled molar mass, complex architectures and copolymer composition distributions intended for biomedical and pharmaceutical applications. In the present work, RAFT miniemulsion copolymerizations of methyl methacrylate with acrylic acid and methacrylic acid were conducted to prepare hydrophilic polymer nanoparticles and compare cell uptake results after bioconjugation with bovine serum albumin (BSA), used as a model biomolecule. Obtained results indicate that the RAFT agent 2-cyano-propyl-dithiobenzoate allowed for successful free radical controlled methyl methacrylate copolymerizations and performed better when methacrylic acid was used as comonomer. Results also indicate that poly(methyl methacrylate-co-methacrylic acid) nanoparticles prepared by RAFT copolymerization and bioconjugated with BSA were exceptionally well accepted by cells, when compared to the other produced polymer nanoparticles because cellular uptake levels were much higher for particles prepared in presence of methacrylic acid, which can probably be associated to its high hydrophilicity.

Water-soluble clickable nucleic acid (CNA) polymer synthesis by functionalizing the pendant hydroxyl

Water-soluble single stranded DNA analogs are generated via thiol–ene photo-oligomerization.

Smart branched polymer drug conjugates as nano-sized drug delivery systems

Branched polymers own special properties derived from their intrinsic characteristics. These properties make them ideal candidates to be used as carriers for an improved generation of polymer-drug conjugates.

Effects of architecture on the stability of thermosensitive unimolecular micelles

The influence of architecture on polymer interactions is investigated and differences between branched and linear copolymers are found. A comprehensive picture is drawn with the help of a fluorescence approach (using pyrene and 4HP as probe molecules) together with IR or NMR spectroscopy and X-ray/light scattering measurements. Five key aspects are addressed: (1) synergistic intramolecular complexation within miktoarm stars. The proximity of thermoresponsive poly(propylene oxide) (PPO) and poly(dimethylaminoethyl methacrylate) (PDMAEMA) within a miktoarm star leads to complexation between these weakly interacting partners. Consequently, the original properties of the constituents are lost, showing hydrophobic domains even at low temperatures, at which all homopolymers are water soluble. (2) Unimolecular micelles for miktoarm stars. The star does not exhibit intermolecular self-assembly in a large temperature range, showing unimers up to 55 °C. This behavior was traced back to a reduced interfacial tension between the PPO-PDMAEMA complex and water (PDMAEMA acts as a "microsurfactant"). (3) Unimolecular to multimolecular micelle transition for stars. The otherwise stable unimolecular micelles self-assemble above 55 °C. This aggregation is not driven by PPO segregation, but by collapse of residual PDMAEMA. This leads to micrometer-sized multilamellar vesicles stabilized by poly(ethylene oxide) (PEO). (4) Prevention of pronounced complexation within diblock copolymers. In contrast to the star copolymers, PPO and PDMAEMA adapt rather their homopolymer behavior within the diblock copolymers. Then they show their immanent LCST properties, as PDMAEMA turns insoluble at elevated temperatures, whereas PPO becomes hydrophobic below room temperature. (5) Two-step micellization for diblock copolymers. Upon heating of linear copolymers, the dehydration of PPO is followed by self-assembly into spherical micelles. An intermediate prevalence of unimolecular micelles is revealed in a small temperature window between PPO collapse and self-assembly of PEO-b-PPO. Also for PPO-b-PDMAEMA, PPO segregation prevails after initial weak complexation, leading to micelles with a PPO core. Considerable amounts of water are entrapped within the collapsed PDMAEMA domains above 55 °C (skin effect), preventing PPO-PDMAEMA complexation within precipitating PPO-b-PDMAEMA. Further, collapsed PDMAEMA is rather polar as sensed by pyrene and 4HP. In summary, advanced macromolecular architectures can lead to an unprecedented intramolecular self-assembly behavior, where internal complexation prevents intermolecular aggregation.

Synthesis of carboxylic block copolymers via reversible addition fragmentation transfer polymerization for tooth erosion prevention

Dental professionals are seeing a growing population of patients with visible signs of dental erosion. The approach currently being used to address the problem typically leverages the enamel protection benefits of fluoride. In this report, an alternative new block copolymer with a hydrophilic polyacrylic acid (PAA) block and a hydrophobic poly(methyl methacrylate) (PMMA) block was developed to similarly reduce the mineral loss from enamel under acidic conditions. This series of PMMA-b-PAA block copolymers was synthesized by reversible addition fragmentation transfer (RAFT) polymerization. Their structures were characterized by gel permeation chromatography (GPC) and (1)H nuclear magnetic resonance (NMR) spectra. The molar fractions of acrylic acid (AA) in the final block copolymer were finely controlled from 0.25 to 0.94, and the molecular weight (Mn) of PMMA-b-PAA was controlled from 10 kDa to 90 kDa. The binding capability of the block copolymer with hydroxyapatite (HAP) was investigated by ultraviolet-visible spectroscopy (UV-Vis) and Fourier transform infrared (FTIR) spectroscopy. FTIR spectra confirmed that the PMMA-b-PAA block copolymer could bind to HAP via bridging bidentate bonds. Both UV-Vis and FTIR spectra additionally indicated that a high polymer concentration and low solution pH favored the polymer binding to HAP. The erosion-preventing efficacy of the PMMA-b-PAA block copolymer in inhibiting HAP mineral loss was quantitatively evaluated by atomic absorption spectroscopy (AAS). Based on the results, polymer treatment reduced the amount of calcium released by 27% to 30% in comparison with the unprotected samples. Scanning electron microscope (SEM) observations indicated that PMMA-b-PAA polymer treatment protected enamel from acid erosion. This new amphiphilic block copolymer has significant potential to be integrated into dentifrices or mouthrinses as an alternative non-fluoride ingredient to reduce tooth erosion.

Thermosensitivity of bile acid-based oligo(ethylene glycol) stars in aqueous solutions

Amphiphilic star-shaped oligo(ethylene glycol)s with a hydrophobic bile acid core and varying number of hydrophilic arms have been made. Their thermal behavior in aqueous solutions depends on the number rather than the length of the arms. The two-armed lithocholate derivative showed the strongest tendency for association and exhibited the lowest cloud point (79 °C) of the oligomers made, as well as another phase separation at a lower temperature (31 °C). The "double thermosensitivity" arising both from the salt-dependent LCST of the oligo(ethylene glycol) segments and the temperature-responsive self-assembly of amphiphilic bile acid derivative provides an interesting path in the design of bile acid-based smart materials.

Association behavior of star-shaped pH-responsive block copolymer: four-arm poly(ethylene oxide)-b-poly(methacrylic acid) in aqueous medium

A four arm pH-responsive poly(ethylene oxide)-b-poly(methacrylic acid) block copolymer was synthesized by atom transfer radical polymerization technique. The conformation transition over the course of neutralization was investigated using a combination of potentiometric and conductometric titrations, dynamic and static light scattering, and transmission electron microscopy. The multiarm block copolymer existed as an extended unimer at high pH due to the negatively charged carboxylate groups and hydrophilic poly(ethylene oxide) segments. The block copolymers self-assembled into core-shell micelles and large spherical aggregates that flocculated at low degree of neutralization (alpha). Such behavior is controlled by the fine balance of electrostatic, hydrophobic, and hydrogen bond interactions. The hydrodynamic radius (R(h)) of the aggregates was approximately 84 nm at alpha of 0.3, and it decreased to 63 and 46 nm at alpha approximately 0.2 and 0.1, respectively, as a result of the reduced electrostatic interaction between ionized carboxylate groups. The thermodynamic parameters obtained from isothermal titration calorimetric technique in different salt concentrations indicated that the energy to extract a proton from a charged polyion was reduced by the addition of salt, which favors the neutralization process.

Synthesis of amphiphilic poly(tetraethylene glycol succinate) and the thermosensitivity of its aggregation in water

Amphiphilic biodegradable polyester, poly(tetraethylene glycol succinate) (PTEGSuc), was synthesized via melt polycondensation of tetraethylene glycol and succinic acid on catalysis of p-toluenesulfonic acid. It was observed that PTEGSuc could self-assemble into micelles in water. In addition, thermosensitivity of PTEGSuc aggregation in water was first found in the experiment, and the critical aggregation temperatures could be controlled by solution concentration. Transmission electron microscopy was used to investigate the micellar morphologies of PTEGSuc in different solvents. It was found that particle shape is almost round although the micellar morphology is different depending on the solvent used. Based on the perfect properties, especially in micelle formation and thermosensitivity, PTEGSuc is promising in biomedical field as carrier of drug delivery system, scaffold of tissue engineering, and other medical devices.